1
Biosecu i y isks om weeds in c op seed lo s impo ed in o
Canada: p e alence, ends, and he bicide esis ance
Jesse M. Rubens ein1, Philip E. Hulme1, Ch is ophe E. Buddenhagen2, M. Philip Rols on3,
John G. Hamp on4
1 Depa men o Pes Managemen and Conse a ion, Lincoln Uni e si y, Ch is chu ch, New Zealand
2 AgResea ch L d., Hamil on, New Zealand
3 Seed Indus y Resea ch Cen e, Ch is chu ch, New Zealand
4 Depa men o Ag icul u al Sciences, Lincoln Uni e si y, Ch is chu ch, New Zealand
Co esponding au ho : Jesse M. Rubens ein ([email p o ec ed])
Copy igh : © Jesse M. Rubens ein e al.
This is an open access a icle dis ibu ed unde
e ms o he C ea i e Commons A ibu ion
License (A ibu ion 4.0 In e na ional – CC BY 4.0).
Resea ch A icle
Abs ac
The in e na ional c op seed ade is a majo pa hway o he unin en ional in oduc ion o non-na i e in-
asi e plan species and he bicide- esis an weeds, posing biosecu i y h ea s o ag icul u e and ecosys ems.
Howe e , published s udies examining weed con aminan s in c op seed emain sca ce. To add ess his, we
analysed Canadian Food Inspec ion Agency (CFIA) moni o ing da a o 2,080 andomly sampled c op
seed lo s impo ed om he Uni ed S a es o Ame ica (USA) be ween 2007 and 2019. Bo h na ions a e
majo playe s in he global seed ade, making hem key biosecu i y case s udies. We epo ed 262 con-
aminan species: 70% we e in oduced in Canada, 23% we e na i e, and 7% had no been p e iously
eco ded (absen ) in Canada. Gene al weeds (no also impo ed as c ops) comp ised 63% o con ami-
nan species; he emaining species we e classi ied as seed o ano he c op. CFIA-classi ied noxious weeds
(Classes 1–5) made up 12% o he con aminan species. Mos con aminan s we e associa ed wi h only one
o wo c op species. The e was a decline in gene al and noxious weeds, and noxious weeds we e epo ed
signi ican ly less han non-noxious weeds o e he s udy pe iod. En y-p ohibi ed species (Class 1) we e
a e, limi ed o ou eco ds o Cuscu a spp. We iden i ied 14 gene al weed species cu en ly absen om
Canada, no ably he equen ly epo ed T i olium esiculosum, along wi h Galium pa isiense, To ilis nodo-
sa, and T i olium hi um, all es ablished in clima ically simila egions o he USA, as well as B omus ca ha -
icus and Eupho bia aleppica, iden i ied as en i onmen al and ag icul u al h ea s. Eigh addi ional species,
such as Ape a spica- en i, cu en ly limi ed o one Canadian p o ince, pose a po en ial domes ic sp ead
isk. Repo ed Class 2 CFIA noxious weeds, including Ci sium a ense, Con ol ulus a ensis, and Elymus
epens, a e o conce n as hei ecological ange is no ully ealised in Canada. Chenopodium album was he
mos widesp ead gene al weed de ec ed ac oss c op species. Con aminan s wi h a known his o y o he -
bicide esis ance in he USA bu no in Canada inc eased signi ican ly o e ime (e.g., So ghum halepense,
Poa annua), while hose esis an in one Canadian p o ince (B omus ec o um) isk u he sp ead in Cana-
da. The in oduc ion o new esis ance is o conce n when a con aminan species is epo ed in a c op ype
in Canada and documen ed as he bicide- esis an in he same c op ype in he USA (Poa annua in o age
and u seed lo s). Regula o y conce ns include impo ing c ops ha a e also classi ied as noxious o p ob-
lema ic weeds (B omus ec o um, Poa annua), pe mi ing con aminan s absen om Canada in seed lo s,
and he dual classi ica ion o species ha a e na i e bu also en y-p ohibi ed (Cuscu a campes is). Ou
s udy highligh s ha expanded global seed ade necessi a es ongoing seed lo moni o ing, isk assessmen ,
and adap i e egula ions o help sa egua d ag icul u e and biodi e si y wi hou hinde ing ade.
Key wo ds: Analy ical pu i y, bo de secu i y, con aminan , in asion biology, in asi e, noxious,
pa hway isk, ade pa hway
Academic edi o : Mo i z on de Lippe
Recei ed:
2 July 2025
Accep ed:
10 Sep embe 2025
Published:
8 Oc obe 2025
Ci a ion: Rubens ein JM, Hulme
PE, Buddenhagen CE, Rols on MP,
Hamp on JG (2025) Biosecu i y isks
om weeds in c op seed lo s impo ed
in o Canada: p e alence, ends,
and he bicide esis ance. NeoBio a
103: 1–30. h ps://doi.o g/10.3897/
neobio a.103.163919
NeoBio a 103: 1–30 (2025)
DOI: 10.3897/neobio a.103.163919
Ad ancing esea ch on alien species and biological in asions
A pee - e iewed open-access jou nal
NeoBio a
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NeoBio a 103: 1–30 (2025), DOI: 10.3897/neobio a.103.163919
Jesse M. Rubens ein e al.: Biosecu i y isks om weed seeds in impo ed c op seed o Canada
In oduc ion
Canada plays a p ominen ole in he global seed ade as a leading p oduce ,
p ocesso , and expo e o high-quali y c op seed, engaging in ade wi h app ox-
ima ely wo- hi ds o coun ies wo ldwide (AAFC 2019; Seeds-Canada 2024). I
is a p ima y supplie o seed o key c ops such as canola, accoun ing o 22% o
global canola seed p oduc ion (USDA 2025). The seed indus y makes a signi i-
can con ibu ion o Canada’s economy, gene a ing app oxima ely CAD $6 bil-
lion annually in di ec and indi ec economic impac s (all subsequen mone a y
alues a e epo ed in CAD). I suppo s mo e han 63,000 jobs, p o ides $2.26
billion in wages and sala ies, and gene a es $2.8 billion in seed sales o Canadian
a me s (AAFC 2019).
Canada is globally anked among he op i e as es -g owing impo e s o seed
o sowing, wi h he o al alue o impo ed seed exceeding he alue o expo -
ed seed by 84% (OEC 2023; S a is ics Canada 2025). A key con ibu o o his
g ow h has been impo s om he Uni ed S a es o Ame ica (USA), Canada’s la g-
es c op seed ade pa ne by bo h dolla alue and onnage (USDA 2024). Since
2019, Canada has impo ed an a e age o $467 million in seed annually om he
USA, ep esen ing 63% o he o al alue o seed impo s om all ading pa ne s.
This accoun s o 85% (137,468 onnes) o he o al olume o all seed impo -
ed annually in o Canada (Seeds-Canada 2024). In 2023, he p ima y c op seeds
impo ed om he USA in o Canada we e maize (co n) (55,170 onnes), o age
and g ass seed (27,365 onnes), pulses (16,926 onnes), soybeans (14,279 onnes),
and canola (6,534 onnes) (Seeds-Canada 2024). Addi ionally, he USA has he
po en ial o expo $11.83 million mo e in c op seed o Canada han i cu en ly
does, highligh ing oppo uni ies o expand ade be ween he wo coun ies (OEC
2023), a po en ial ha will equi e con inued c oss-bo de coope a ion and eg-
ula o y alignmen . A he same ime, he g ow h o Canada’s seed impo ma ke
inc eases he isk o weed incu sions ia con aminan s in c op seed lo s, unde sco -
ing he need o obus biosecu i y measu es.
The a e o new plan species in oduc ions in Canada has g own exponen ially
in ecen decades wi h he expansion o global ade and a el (ECCC 2017). An
es ima ed 58% o in asi e plan species in Canada esul ed om delibe a e in o-
duc ions, including ag onomic c ops, landscape plan s, o namen als, and medici-
nal plan s (CFIA and McClay 2008). The emaining plan in oduc ions occu ed
unin en ionally, p ima ily as con aminan s in impo ed ag icul u al seed lo s, g ain
and ce eal impo s, soil, machine y, ehicles, o as s owaways on ca go and passen-
ge ships (ECCC 2017).
Ag icul u al seed lo s ha e his o ically been a signi ican pa hway o unin en-
ional in oduc ions o na u alised weeds a ound he wo ld (Mack and Lonsdale
2001), pa icula ly when hese weeds a e in oduced in o egions wi h clima es
simila o hose whe e hey a e al eady es ablished (Hulme 2024). The in e na ion-
al c op seed ade con inues o se e as a signi ican in oduc o y pa hway o weed
seeds, making i a c i ical conce n o biosecu i y managemen (Buddenhagen e
al. 2021). E ec i e managemen o hese pa hways equi es unde s anding he
mechanisms o in oduc ion and sp ead o in asi e species, as well as hei eco-
nomic and ecological consequences (Seebens e al. 2022).
The in oduc ion o non-na i e plan species h ough pa hways such as ag icul-
u al seed lo impo s has in ensi ied he ongoing challenges o weed managemen
3
NeoBio a 103: 1–30 (2025), DOI: 10.3897/neobio a.103.163919
Jesse M. Rubens ein e al.: Biosecu i y isks om weed seeds in impo ed c op seed o Canada
in Canada, esul ing in subs an ial economic, en i onmen al, and heal h impac s
(CFIA 2011). Managing weeds in Canadian pas u es and c ops cos s an es ima ed
$2.2 billion annually, equi alen o oughly 15% o he o al alue o annual plan
p oduc s (CFIA and McClay 2008). O his amoun , g owe s bea be ween $1.1
and $1.5 billion annually in cos s due o inc eased he bicide use and educed c op
yield and quali y (Beckie 2024).
E ec i e weed managemen is c i ical o educing hese cos s and main ain-
ing high c op yields. Wi hou in e en ion, combined es ima es o Canada and
he USA sugges weed in e e ence could educe maize yields by 50%, alued a
$36.1 billion annually (Sol ani e al. 2016), and soybean yields by 52%, alued
a $23.2 billion annually (Sol ani e al. 2017). Whea is also signi ican ly a ec -
ed, wi h po en ial yield losses o 24% in win e whea , alued a app oxima ely
$3 billion annually, and 20% in sp ing whea , alued a $1.9 billion annually
(Flessne e al. 2021). In Canada, e ec i e weed managemen has a g ea e im-
pac on canola yields han e ilise o gene ics, wi h weed in e e ence alone
causing an es ima ed a e age yield loss o 30% (Blackshaw e al. 2011; Ged-
des e al. 2022). Recen inc eases in he bicide esis ance a e u he inc easing
weed con ol cos s, educing managemen e ec i eness, and po en ially leading
o g ea e yield losses (Flessne e al. 2021). Ne e heless, in Canada, he bi-
cide-based weed con ol can s ill yield a e u n o app oxima ely h ee dolla s o
e e y dolla in es ed (S ephenson 2003).
He bicide- esis an (HR) bio ypes ep esen a signi ican and g owing chal-
lenge in Canada, which anks hi d globally o coun ies wi h he highes num-
be o HR weeds, wi h 56 documen ed bio ypes (Heap 2025). Among he mos
p oblema ic a e A ena a ua, Conyza canadensis, and Kochia scopa ia, which ex-
hibi esis ance o commonly used he bicide g oups, including EPSP syn hase
inhibi o s ( hose con aining glyphosa e), ace olac a e syn hase inhibi o s, and
ace yl-CoA ca boxylase inhibi o s (Beckie 2018; Heap and Duke 2018). The i e
mos equen ly epo ed HR weeds in Canada, in o de o occu ence, a e A ena
a ua, Ama an hus e o lexus, Se a ia i idis, Kochia scopa ia, and Ama an hus
powellii (Heap 2025). The challenge posed by HR weeds is pa icula ly acu e in
Wes e n Canada, he coun y’s main egion o c op p oduc ion, whe e nea ly
54% o c opland is a ec ed (Beckie 2018). Key c ops, such as ba ley, a e es-
pecially impac ed by he g owing numbe o esis an weed species in Canada
(Hulme 2022). In Saska chewan (Cen al Canada), annual losses om he bicide
esis ance a e es ima ed a $343 million, due o lowe yields and quali y, as well
as highe weed con ol cos s (Geddes e al. 2024). In esponse, many a me s
a e shi ing om eac i e he bicide use o p e en ion- ocused s a egies aimed a
s opping weed seeds om en e ing he soil in he i s place (Beckie e al. 2019).
This p oac i e app oach equi es main aining high analy ical pu i y in c op seed
lo s and p e en ing he es ablishmen o new he bicide- esis an bio ypes. The
escala ing p e alence o HR weeds in Canada highligh s he need o mo e sus-
ainable and inno a i e managemen s a egies o p o ec bo h ag icul u al p o-
duc i i y and ecosys em heal h.
In addi ion o he bicide esis ance, unde s anding whe he a plan species is
na i e, al eady p esen as an in oduced species, o absen om a coun y is im-
po an o e ec i e weed managemen . These classi ica ions in o m egula o y
p io i ies, guide con ol s a egies, and suppo ea ly de ec ion and esponse (Pyšek
e al. 2004). O he es ima ed 5,124 ascula plan species g owing in Canada,
4
NeoBio a 103: 1–30 (2025), DOI: 10.3897/neobio a.103.163919
Jesse M. Rubens ein e al.: Biosecu i y isks om weed seeds in impo ed c op seed o Canada
app oxima ely 25% (1,295 species) a e in oduced, wi h he emainde consid-
e ed na i e (Desme and B ouille 2013). Among he in oduced species, 486 a e
classi ied as in asi e due o hei impac s on biodi e si y, ecosys em unc ioning,
ag icul u al p oduc i i y, ade, and human heal h (CFIA and McClay 2008).
Dis inguishing in asi e plan species om o he in oduced plan s p esen s a sig-
ni ican egula o y challenge (Hulme 2006). Howe e , accu a ely assessing and
p io i ising hese species is essen ial o educe hei ha m ul impac s, bu doing so
equi es comp ehensi e da a and coo dina ion ac oss mul iple s akeholde s, which
can be bo h logis ically and inancially demanding. Species classi ied as absen ,
meaning no cu en ly known o occu in he coun y, a e o pa icula conce n,
especially when de ec ed as con aminan s in c op seed lo s. Thei p esence may
signal a new in oduc ion pa hway o in asi e species and could lead o ecological
o economic consequences i hey become es ablished.
To mi iga e he isks posed by weeds, Canada has implemen ed measu es o
limi he in oduc ion and sp ead o in asi e weed species, pa icula ly ia ag i-
cul u al seed lo con amina ion. The Canadian Food Inspec ion Agency (CFIA)
en o ces hese egula ions, wi h he Weed Seeds O de (WSO) o he Seeds Ac
being he co ne s one o his isk educ ion amewo k. The WSO aims o p e-
en he in oduc ion o new weed species and limi he p esence o weed seeds
in c op seed sold o impo ed in o Canada (CFIA 2016b). Al hough upda es o
he WSO ha e been in equen (mos ecen ly in 2016), each e ision is in end-
ed o e lec changes in weed dis ibu ion, ad ances in managemen p ac ices,
and eme ging o changing isks om seed impo s. The WSO applies o seeds
used in ag icul u e, esiden ial p oduc s such as wild lowe mix u es, and land
eclama ion (CFIA 2016b). By egula ing weed seeds ac oss hese applica ions,
he WSO plays a c i ical ole in p o ec ing ag icul u al p oduc i i y and p e-
se ing na u al ecosys ems.
In addi ion o he WSO, Canada employs o he egula o y measu es o mi -
iga e weed seed isks and ensu e compliance wi h in e na ional ade s anda ds.
These include he en o cemen o he Plan P o ec ion Ac , which p ohibi s he
impo a ion o c op seed i i is classi ied as, o con ains, a pes plan (CFIA
2019). Canada also equi es impo pe mi s, phy osani a y ce i ica es, and ea -
men documen a ion o e i y ha impo ed seed lo s mee he coun y’s biose-
cu i y s anda ds (CFIA 2016a). The CFIA moni o s seed lo s o compliance wi h
na ional egula ions by sampling and es ing seed lo s o weed seed con amina-
ion. In addi ion o go e nmen o e sigh , he e a e addi ional pu i y s anda ds
equi ing ha seed lo s emain below speci ic h esholds o weed seed con en
and be ee o noxious weeds o quali y as ce i ied seed unde he OECD seed
scheme (Buddenhagen e al. 2022).
Toge he , all hese p ocesses play a c i ical ole in p e en ing he in oduc ion
o in asi e non-na i e plan species, sa egua ding ag icul u al p oduc i i y, and
main aining Canada’s biosecu i y. Non-compliance can impose signi ican cos s,
as con amina ed seed lo s may equi e e-cleaning, e-expo ing, o des uc ion
(Wilson e al. 2016; USDA 2019; Buddenhagen e al. 2022). Collabo a ion wi h
in e na ional egula o y bodies and he implemen a ion o public awa eness ini-
ia i es a e also essen ial o s eng hening biosecu i y sys ems and add essing he
isks posed by global seed ade. In an inc easingly in e connec ed wo ld, e ec i e
and coo dina ed managemen o he c op seed ade pa hway is essen ial o educe
he isk o u u e plan in asions (Hulme 2009).
5
NeoBio a 103: 1–30 (2025), DOI: 10.3897/neobio a.103.163919
Jesse M. Rubens ein e al.: Biosecu i y isks om weed seeds in impo ed c op seed o Canada
S udy aims
To e alua e he ole o in e na ional c op seed ade as a pa hway o he unin en-
ional in oduc ion and sp ead o non-na i e in asi e, p e iously un eco ded, and
he bicide- esis an weed species in Canada, we analysed a unique da ase o o icial
Canadian c op seed lo inspec ions o add ess he ollowing esea ch ques ions:
1. How equen ly a e CFIA-classi ied noxious weeds, gene al weeds (no also
impo ed as c op seed), species no cu en ly known o be p esen in Canada,
and eme ging he bicide- esis an weeds epo ed in impo ed seed lo s, and
do any o hese ca ego ies show signi ican ends o e ime?
2. A e mos con aminan weeds associa ed wi h only a ew c op species, o do
some occu ac oss a b oad ange o c ops?
3. Which con aminan species may pose he g ea es isk o es ablishing o
sp eading, including he in oduc ion o new he bicide- esis an weeds in o
Canada?
4. How do cu en CFIA egula o y classi ica ions and amewo ks align wi h
he po en ial isks associa ed wi h hese con aminan species?
Me hods
Seed lo inspec ion da a
This s udy used o icial inspec ion da a o c op seed lo s impo ed in o Canada
om he USA be ween 2007 and 2019, p o ided by he CFIA Seed Sec ion
(O awa). Moni o ing samples we e collec ed by CFIA seed inspec o s, and he
seed lo s we e analysed wi h accompanying da a compiled by he CFIA Seed
Science and Technology Sec ion (Saska oon), which ope a es an In e na ional
Seed Tes ing Associa ion (ISTA) and ISO 17025-acc edi ed labo a o y. Canada
moni o s impo s om all coun ies, bu gi en ha he USA is i s la ges ad-
ing pa ne o c op seeds (Seeds-Canada 2024), ou analysis ocused exclusi ely
on hese impo s. Du ing his pe iod, he CFIA moni o ed 2,080 andomly
selec ed c op seed lo s om he USA o ensu e compliance wi h Canadian seed
s anda ds. While all sampling da a we e p o ided o us, hese andom samples
ep esen ed only a small ac ion o he o al seed lo s impo ed annually om
he USA in o Canada, and in o ma ion on he o al numbe o impo ed lo s
was no p o ided o us.
Seed lo inspec ion eco ds included he ollowing in o ma ion ele an o ou
analysis: impo ed c op species, con aminan species de ec ed, and sampling yea .
Because a single seed lo can ha e mul iple con aminan s om di e en axa, a
con aminan eco d e e s o any ime a single con aminan axon was epo ed in
a single seed lo . Con aminan s we e iden i ied a he species le el in 70% o cases,
wi h 27% iden i ied a he genus le el and 3% a he amily le el. Repo ing a he
genus and amily le el is no uncommon in o icial inspec ion da a (Rubens ein e
al. 2021), pa icula ly when con aminan s wi hin he same genus a e mo pholog-
ically challenging o dis inguish (James e al. 2014). Because he numbe o seeds
o each con aminan ound in a seed lo was no p o ided o us, we only consid-
e ed he p esence o absence o a con aminan species, a he han i s abundance
(Rubens ein e al. 2023).
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NeoBio a 103: 1–30 (2025), DOI: 10.3897/neobio a.103.163919
Jesse M. Rubens ein e al.: Biosecu i y isks om weed seeds in impo ed c op seed o Canada
Da a p epa a ion
Plan names we e s anda dised using he mos ecen (2025) axonomy lis ed in
he Da abase o Vascula Plan s o Canada (VASCAN) (Desme and B ouille
2013) (h ps://da a.canadensys.ne ). Addi ionally, VASCAN was used o clas-
si y con aminan s based on hei o igin s a us in Canada, iden i ying species
as ei he in oduced, na i e, o absen (Desme and B ouille 2013). Absen
species we e de ined as plan s ha ha e no been epo ed as occu ing in he
wild wi hin Canada (Desme and B ouille 2013). A species was classi ied as
in oduced o na i e o he en i e coun y i i held ei he s a us in a leas one
Canadian p o ince. In cases whe e a species was lis ed as na i e in one p o ince
and in oduced in ano he (e.g., na i e in On a io bu in oduced in B i ish
Columbia), i was classi ied as na i e by de aul . Species lis ed in VASCAN as
excluded o ex i pa ed, o no lis ed a all, we e ca ego ised as absen . Addi ional
de ails on hese classi ica ions can be ound in he VASCAN da abase: h ps://
da a.canadensys.ne / ascan/abou .
Con aminan species we e also classi ied as ei he a ‘gene al weed’ o ‘seed o an-
o he c op’. A species was conside ed seed o ano he c op i i was a decla ed c op
in ano he ins ance wi hin he CFIA impo da ase i sel o i i appea ed as a c op
species in o icial CFIA documen a ion, including he “Canadian Me hods and
P ocedu es o Tes ing Seed” (CFIA 2024a), he ‘App oxima e Numbe o Seeds
pe G am’ sec ion o “The ABCs o Seed Impo a ion in o Canada” (CFIA 2022),
o he “Lis o G ains and Field C ops” (CFIA 2015). Any con aminan species no
mee ing hese c i e ia was ca ego ised as a gene al weed.
Finally, con aminan species we e ca ego ised acco ding o hei o icial
CFIA noxious weed classi ica ion om he WSO, anging om Class 1 o
5 o noxious weeds and Class 6 o all o he con aminan s (CFIA 2016b).
While Class 1 – P ohibi ed Noxious Weed Seeds has a ze o- ole ance policy,
pe missible limi s o he emaining classes (including Class 6) a y depend-
ing on he c op ype and in ended use. These limi s a e ou lined in Schedule
I o he “Seeds Regula ions” (C.R.C., c. 1400), which speci ies he maximum
allowable quan i ies o weed seeds in di e en seed classes (CFIA 2025a). De-
sc ip ions o each CFIA weed seed class a e p esen ed in Table 1 (CFIA 2009,
2011, 2016b, 2025a).
Addi ionally, species we e classi ied as in asi e i hey we e e e enced in he
“In asi e Alien Plan s in Canada” echnical epo by CFIA and McClay Ecosci-
ence (CFIA and McClay 2008). The ull lis o 486 in asi e species e e enced in
he epo was p o ided o ou s udy by CFIA.
The In e na ional He bicide-Resis an Weed Da abase (h ps://www.weed-
science.o g) was used o iden i y con aminan species ha ha e his o ically
e ol ed he bicide esis ance in weedy con ex s in Canada and he USA (Heap
2025). Howe e , when he con aminan was a seed o ano he c op, he species
was no ca ego ised as he bicide- esis an . Fo example, al hough he bicide- e-
sis an a ie ies o Zea mays (maize) a e widely cul i a ed, hey ha e no been
documen ed as he bicide- esis an weeds in ei he coun y and we e he e o e
excluded om he analysis. In con as , c op species such as Lolium mul i-
lo um, which also appea ed as con aminan s in his da ase , we e included
because hey ha e been eco ded as he bicide- esis an weeds in bo h Canada
and he USA.
7
NeoBio a 103: 1–30 (2025), DOI: 10.3897/neobio a.103.163919
Jesse M. Rubens ein e al.: Biosecu i y isks om weed seeds in impo ed c op seed o Canada
S a is ical analysis
We analysed hi een consecu i e yea s o seed lo sampling da a (2007–2019),
a e aging 160 inspec ions pe yea , o a o al o 2,080 seed lo s impo ed om he
USA. Gi en ha 70% o con aminan eco ds we e iden i ied a he species le el,
he analysis was conduc ed a his axonomic le el. Genus- and amily-le el eco ds
we e excluded om all analyses, excep in Table 2, which lis s Class 1 – P ohib-
i ed Noxious Weed Seeds. Due o he high egula o y conce n associa ed wi h
en y-p ohibi ed weeds, all ele an eco ds we e e ained in his able ega dless o
hei le el o axonomic esolu ion.
The annual pe cen age o con aminan species in each ca ego y (e.g., na i e, in-
oduced, noxious) was calcula ed as he numbe o species in he ca ego y di ided
by he o al numbe o con aminan species eco ded o ha yea .
A non-pa ame ic Mann–Kendall es was used o e alua e i he e was a signi -
ican upwa d o downwa d empo al end in he p e alence o con aminan spe-
cies ca ego ised by o igin s a us (absen , in oduced, o na i e), noxious weed s a us
(Classes 1 o 5), gene al weeds, and species wi h a his o y o he bicide esis ance. This
me hod is well-sui ed o analysing non-pa ame ic da a and de ec ing mono onic
ends in ime se ies wi hou equi ing assump ions o no mali y (Yue e al. 2002).
Addi ionally, a Wilcoxon signed- ank es was used o compa e he epo ing
equency o non-na i e species in oduced in o Canada wi h ha o na i e species
and species absen om Canada, he p e alence o Class 1 o 5 noxious weeds wi h
Class 6 species, and gene al weeds wi h con aminan s classi ied as seed o ano h-
e c op (Wilcoxon e al. 1970). A Spea man’s ank co ela ion was pe o med o
e alua e he ela ionship be ween he numbe o con amina ed seed lo s and he
o al numbe o inspec ed seed lo s o he op 20 mos equen ly inspec ed c ops,
ep esen ing 83% o he da ase . This me hod was selec ed o i s obus ness o
ou lie s and i s sui abili y o non-linea ela ionships, wi hou assuming no mali-
y (Hauke and Kossowski 2011). All igu es we e gene a ed using Py hon wi h he
Ma plo lib and Pandas lib a ies (Hun e 2007; McKinney 2010).
Table 1. CFIA noxious weed seed classes and hei co esponding ca ego y desc ip ions.
CFIA class Noxious weed
seed ca ego y Class desc ip ion Composi ion
Class 1 P ohibi ed
noxious
Includes some species no ye p esen in Canada (absen ), as well as species unde o icial
con ol due o incomple e ecological ange expansion. Con ol e o s ocus on e adica ion o
con ainmen . These species a e s ic ly p ohibi ed in all impo ed and domes ic seed lo s due o
hei po en ial economic, en i onmen al, and heal h isks.
25 species, 1 genus
(Cuscu a spp.)
Class 2 P ima y noxious Species p esen in Canada bu no ye a hei ull ecological ange. These weeds a e no unde
o icial con ol bu can educe seed alue, in e e e wi h ag icul u al p oduc ion, and pose isks o
economic and human heal h.
36 species
Class 3 Seconda y
noxious
Rela i ely common and widesp ead ac oss Canada. These weeds lowe seed alue o dis up ag icul u al
uses bu a e gene ally easie o manage in cul i a ed ields compa ed o mo e es ic i e classes.
29 species, 1 genus
(Rumex spp.)
Class 4 Seconda y
noxious
Rela i ely common and widesp ead ac oss Canada. These weeds lowe seed alue o dis up ag icul u al
uses bu a e gene ally easie o manage in cul i a ed ields compa ed o mo e es ic i e classes.
2 species, 3 gene a
Class 5 Noxious Includes species om Class 4 along wi h wo addi ional species. Common ac oss Canada, hey
can educe seed alue o in e e e wi h ag icul u al use. The key dis inc ion be ween Class 4 and
Class 5 lies in he ype o seed mix u e in which hey a e ound: Class 4 species occu in u g ass
seed lo s, whe eas Class 5 species a e ound in lawn o g ound co e mix u es.
4 species, 3 gene a
Class 6 O he
(non-noxious)
This class includes widesp ead species in Canada ha may wa an moni o ing o main ain seed
quali y and p e en sp ead in o new p o inces, as well as absen species, some o which ha e no
been o mally assessed bu may equi e biosecu i y a en ion.
All o he s
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Jesse M. Rubens ein e al.: Biosecu i y isks om weed seeds in impo ed c op seed o Canada
Resul s
Be ween 2007 and 2019, Canada moni o ed 113 c op species and se en seed mix-
u es impo ed om he USA. The 20 mos equen ly inspec ed species (Table 2)
made up 83% o all inspec ions and we e p ima ily a able, o age, and u c ops.
The c ops wi h he highes p opo ion o seed lo s con aining con aminan s we e
T i olium epens (whi e clo e ) a nea ly 93%, Dac ylis glome a a (o cha d g ass) a
89%, and lawn seed mix u es a 88%. Howe e , hese con amina ion a es should
be in e p e ed wi h cau ion, as hey do no e lec he noxious weed classi ica ion
o o igin s a us o he con aminan s, which a e add essed in subsequen sec ions.
Addi ionally, he e was no signi ican co ela ion be ween he numbe o seed lo s
inspec ed wi hin each c op and he co esponding p opo ion ound o be con-
amina ed (Spea man’s co ela ion, p = 0.560). Fo ins ance, Zea mays, he mos
equen ly inspec ed c op, had he lowes con amina ion a e, a less han 2%.
O e iew o con aminan species
A o al o 262 con aminan species we e epo ed ac oss all o icially moni o ed
seed lo s om he USA (Suppl. ma e ial 1: able S1). O hese, he majo i y (166
species, 63%) we e classi ied as gene al weeds ha a e no also impo ed as c ops
in o Canada (Fig. 1). The emaining con aminan species we e conside ed seed
o ano he c op. Based on hei o igin s a us wi hin Canada, 182 species (70%)
we e classi ied as in oduced, 61 species (23%) as na i e, and 19 species (7%) as
absen , indica ing hey a e no cu en ly p esen in Canada (Fig. 1). Rega ding
Table 2. Top 20 mos inspec ed c op species o seed lo s impo ed om he USA. Species a e lis ed in descending o de by equency o
inspec ion anking.
C op F equency o inspec ion anking P ima y c op ypes(s) Pe cen age o seed lo s con amina ed
Zea mays 1 A able 1.7
Poa p a ensis 2 Fo age, u 53.8
Phaseolus ulga is 3 A able 2.3
Lolium pe enne 4 Fo age, u 59.1
Pisum sa i um 5 A able 3.1
Lolium mul i lo um 6 Fo age 63.3
B assica napus 7 A able 6.5
Medicago sa i a 8 Fo age 42.1
T i olium p a ense 9 Fo age 74.3
Glycine max 10 A able 3.0
Lolium a undinaceum (Fes uca a undinacea) 11 Fo age, u 75.0
Dac ylis glome a a 12 Fo age 89.1
Raphanus sa i us 13 Fo age, ege able 35.8
Fes uca ub a 14 Fo age, u 53.2
T i olium epens 15 Fo age 92.9
So ghum × d ummondii 16 Fo age 11.1
Fes uca b e ipila 17 Fo age, u 44.0
Echinochloa esculen a 18 Fo age 77.3
T i olium inca na um 19 Fo age 60.0
Lawn mix u e 20 Tu 88.2
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Jesse M. Rubens ein e al.: Biosecu i y isks om weed seeds in impo ed c op seed o Canada
CFIA noxious weed classi ica ions, 31 species (12%) we e assigned o Classes 1
h ough 5 (noxious), while he emaining 231 species (88%) we e classi ied as
Class 6 (non-noxious) (Fig. 1). The la e ca ego y includes con aminan s ha a e
ei he al eady widesp ead in Canada o a e absen , some o which ha e no ye
been o mally e alua ed o noxious designa ion. Addi ionally, 126 species (48%)
we e lis ed as in asi e (Suppl. ma e ial 1: able S1) acco ding o he “In asi e Alien
Plan s in Canada” echnical epo (CFIA and McClay 2008).
T ends ela ed o gene al weeds and CFIA noxious weeds
Fig. 2 p esen s empo al ends o gene al weeds (species no also impo ed as c op
seeds) and CFIA-classi ied noxious weeds (Classes 1 o 5). Gene al weeds showed
a signi ican dec ease o e ime (Mann–Kendall, Tau = -0.590, p = 0.004). A de-
c easing end was also obse ed o CFIA-classi ied noxious weeds (Tau = -0.333),
bu i was no s a is ically signi ican (p = 0.129). Class 1 o 5 noxious weeds we e
epo ed signi ican ly less o en han Class 6 species, occu ing a 69% lowe e-
quency on a e age (Wilcoxon signed- ank es , p = 0.0002). In con as , gene al
weeds and con aminan s classi ied as seed o ano he c op we e epo ed a simila
a es, wi h no signi ican di e ence be ween he wo g oups (p = 0.414). Fig. 2
shows he annual pe cen age o epo ed gene al weeds and CFIA-classi ied nox-
ious weeds (Classes 1 o 5), wi h he emaining p opo ion each yea ep esen ing
o he ca ego ies (Class 6 and seed o ano he c op), summing o 100%.
Th oughou he s udy pe iod, de ec ions o p ohibi ed noxious weeds (Class 1)
we e a e, wi h only ou epo s (Table 3): one seed lo con aining Cuscu a campes-
is and h ee mo e wi h Cuscu a spp. (iden i ied only o genus le el). Two o hese
epo s we e ound in seed lo s o Rudbeckia hi a (black-eyed Susan), a widely
cul i a ed o namen al lowe species in Canada, and he o he wo in T i olium
p a ense ( ed clo e ). P ima y noxious weeds (Class 2) we e somewha mo e
common, comp ising nine species (3% o all con aminan s) ac oss 36 seed lo s
(Table 3). The mos equen ly epo ed o his class we e Ci sium a ense (9 seed
lo s), Elymus epens (9), and Con ol ulus a ensis (7). All Class 1 and 2 species we e
in oduced, apa om Cuscu a campes is, which is na i e. The c op species mos
equen ly associa ed wi h hese noxious weeds we e Lolium pe enne (pe ennial
Figu e 1. Classi ica ion o con aminan species by con aminan ype (gene al weed o seed o ano he impo ed c op), o igin s a us (in o-
duced, na i e, o absen in Canada), and CFIA noxious weed classi ica ion (Class 1 o 5 o Class 6). All species, ega dless o o igin s a us,
we e also assigned o one o he six CFIA weed classes.
16
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Jesse M. Rubens ein e al.: Biosecu i y isks om weed seeds in impo ed c op seed o Canada
example, Rubens ein e al. (2021) analysed o e 42,000 seed lo s en e ing New
Zealand om mo e han 90 coun ies and ound en y-p ohibi ed weeds in jus
0.06% o cases. Re lec ing simila p io i ies, New Zealand’s Minis y o P ima y
Indus ies also classi ies he en i e Cuscu a genus as en y-p ohibi ed in seed lo s
(MPI 2025), and hei domes ic seed indus y includes Cuscu a spp. on a lis o
14 ‘undesi able weeds’ (Young 1984). The p esence o hese species in a domes ic
seed lo in New Zealand can p e en i om achie ing seed ce i ica ion and sub-
s an ially educe i s ma ke alue, p o iding a s ong incen i e o indus y com-
pliance. The economic, ecological, and heal h isks associa ed wi h such species
help explain why bo h egula o s and seed p oduce s consis en ly p io i ise hei
exclusion, whe he in Canada, New Zealand, o o he seed-impo ing na ions.
P ima y noxious weeds (Class 2), al hough no en y-p ohibi ed, we e mo e e-
quen ly epo ed. The mos commonly epo ed we e Ci sium a ense and Elymus
epens (each in 9 seed lo s), ollowed by Con ol ulus a ensis (7). These species a e
al eady p esen in Canada bu ha e no eached hei ull ecological ange and a e
no subjec o o icial con ol (CFIA 2011). Addi ionally, Class 2 weeds can lowe
seed alue, in e e e wi h ag icul u al p oduc ion, and pose b oade economic and
en i onmen al isks. Thei epea ed de ec ion in impo ed seed lo s unde sco es
he need o con inued moni o ing.
Regula o y complexi ies: na i e species classi ied as en y-p ohibi ed
The emphasis on excluding speci ic weeds becomes mo e complex when he species
in ques ion is bo h en y-p ohibi ed and na i e o he impo ing coun y. This was
he case o Cuscu a campes is, a Class 1 weed epo ed in he CFIA da ase ha is
na i e o Canada and al eady es ablished in all he sou he n p o inces excep New
B unswick (Desme and B ouille 2013). O he na i e species epo ed as noxious
weeds in seed lo s included Amb osia a emisii olia (Class 3), Galium apa ine (Class
3), Panicum capilla e (Class 4 o 5), and Panicum i ga um (Class 4 o 5). While
hese species a e no p ohibi ed in seed lo s, hei p esence is egula ed. This dual
classi ica ion, especially in he case o p ohibi ed bu also na i e species, can p es-
en egula o y challenges. Fede al agencies o e see seed impo s, while p o inces
manage es ablished weeds, and his di ision o esponsibili ies may lead o en o ce-
men complica ions and con usion o indus y, pa icula ly when a p ohibi ed
species is al eady widesp ead in some egions o he coun y bu no o he s.
Regula o y o e lap: c ops also classi ied as noxious weeds
Addi ional egula o y complica ions a ise when species ha a e noxious o o he wise
p oblema ic weeds a e impo ed in en ionally as c op seed. While Class 1 noxious
weeds a e p ohibi ed om en e ing Canada, species om o he noxious classes may s ill
en e , ei he as seed lo con aminan s o , in some cases, as impo ed c ops. Al hough
ela i ely uncommon in he CFIA da ase , his occu ed o B omus ec o um (Class
3), as well as Panicum miliaceum (Class 4 o 5) and Panicum i ga um (Class 4 o 5).
O hese, only P. miliaceum (p oso mille ) is o mally lis ed in CFIA documen a ion
o c op species (CFIA 2022, 2024a). The legal impo a ion o such species may pose a
isk o mo e local weed con ol e o s i hese plan s es ablish and sp ead.
B omus ec o um (downy b ome) is o pa icula conce n, as i was iden i ied as
one o he mos widely dis ibu ed con aminan species ac oss mul iple c ops. I is
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Jesse M. Rubens ein e al.: Biosecu i y isks om weed seeds in impo ed c op seed o Canada
al eady ecognised as p oblema ic due o i s apid sp ead and pe sis ence as a win e
annual in wes e n No h Ame ica. I dis up s c opping sys ems, deg ades pas u e-
lands, and eadily es ablishes in bo h na u alised and dis u bed habi a s (Geddes
and Pi man 2022). Despi e hese impac s, he CFIA no es ha B. ec o um ‘has a
dual ole as a se ious weed and an impo an o age’ c op (CFIA 2017b). Howe e ,
i emains one o he mos p oblema ic weeds in c ops like win e whea , whe e
i compe es agg essi ely wi h he c op and can cause subs an ial yield losses i le
unmanaged (Os lie and Howa 2013). I is also conside ed one o he mos ou-
blesome he bicide- esis an weeds in pa s o he USA, pa icula ly in he G ea
Plains (B unha o e al. 2022). While he bicide- esis an popula ions ha e been
epo ed in bo h o age and a able sys ems in he USA since he mid-1990s (Heap
2025), esis an bio ypes we e no de ec ed in Canada un il 2021, when hey ap-
pea ed in a canola ield (Geddes and Pi man 2022). This unde sco es he need o
heigh ened a en ion o i s po en ial long- e m impac on Canadian ag icul u e.
Cases like hese illus a e a b oade challenge aced by biosecu i y sys ems, in-
cluding in Canada, whe e he same species can be legally impo ed as c op seed
while being managed as a p oblema ic weed a he p o incial le el. The CFIA, as
he ede al body esponsible o seed impo egula ion, applies he Weed Seeds
O de o de e mine pe missible species and h esholds. Howe e , he esponsibili y
o managing weed impac s pos -en y o en alls o p o incial go e nmen s and
p oduce s, who may be ying o supp ess he e y species a i ing legally h ough
impo s. Wi hou s ong coo dina ion be ween impo policies and domes ic weed
con ol s a egies, high- isk species may es ablish, complica ing e adica ion o con-
ainmen e o s once hey a e widesp ead.
A simila si ua ion exis s wi h Poa annua (annual blueg ass), which is no clas-
si ied as a noxious weed in Canada bu is cu en ly designa ed as a c op in CFIA
documen a ion (CFIA 2022, 2024a). Despi e i s c op designa ion, P. annua has
been ega ded as a p oblema ic weed in empe a e egions wo ldwide, including
Canada (Wa wick 1979; Hu chinson and Seymou 1982). I is pa icula ly di i-
cul o con ol in u g ass and o age sys ems due o widesp ead he bicide esis-
ance, including glyphosa e esis ance (Heap and Duke 2018). He bicide- esis an
P. annua has been epo ed in wel e coun ies ac oss ou con inen s, including
he USA, al hough no esis an popula ions ha e ye been eco ded in Canada
(Heap 2025). In he CFIA da ase , P. annua was one o he mos equen ly e-
po ed con aminan s, appea ing in seed lo s o 13 di e en c op species. Al hough
i was no impo ed as a c op du ing he hi een-yea s udy pe iod, i s equen
occu ence as a con aminan , wide dis ibu ion ac oss Canada, esis ance his o y
ab oad, and s a us as a p oblema ic weed in mul iple ading pa ne coun ies
sugges i s cu en c op s a us may wa an eassessmen (Desme and B ouille
2013; Rubens ein e al. 2023).
Biosecu i y conside a ions o absen species
Beyond he egula o y classi ica ion o noxious weeds, he o igin s a us o con am-
inan species o e s a aluable lens o assessing biosecu i y isks. Al hough in o-
duced species we e he mos equen ly epo ed o igin ype, absen species ( hose
no cu en ly p esen in Canada) wa an pa icula a en ion. Thei de ec ion in
seed lo s indica es a po en ial pa hway o new plan in oduc ions. I hese species
es ablish a e sowing, hey may become in asi e, pa icula ly in Canadian egions
18
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Jesse M. Rubens ein e al.: Biosecu i y isks om weed seeds in impo ed c op seed o Canada
wi h clima es simila o hose whe e he species a e al eady es ablished. This isk
is heigh ened o species wi h ai s associa ed wi h in asi eness o he abili y o
con amina e a b oad ange o c op ypes.
Regula o y complexi ies: absen species pe mi ed in seed lo s
Among he gene al weeds no ye p esen in Canada, all we e classi ied as Class
6 unde he Weed Seeds O de (WSO), a ca ego y ha excludes noxious weeds.
This class includes bo h common weeds al eady widesp ead in Canada, such as
Chenopodium album, and species no ye eco ded in he coun y, many o which
ha e no been o mally assessed o biosecu i y isk. Howe e , h ee o he absen
gene al weeds, B omus ca ha icus, Eupho bia aleppica, and T i olium esiculosum,
a e lis ed in p elimina y weed isk analysis documen s ecen ly published by CFIA
(CFIA 2025b). These species we e selec ed o ea ly assessmen due o hei po-
en ial phy osani a y conce n and ha e unde gone he i s s age o isk analysis,
al hough no o mal egula o y decisions ha e been inalised. The assessmen sug-
ges s ha B omus ca ha icus ( escue g ass) poses an en i onmen al h ea , while
Eupho bia aleppica (Aleppo spu ge) may p esen a isk o ag icul u e.
Rega dless o hei s a us, all Class 6 species a e pe missible in seed lo s, p o-
ided hei p esence emains below he allowable h eshold o he ele an c op
ype and seed g ade (CFIA 2016b). This p o ision may e lec a egula o y gap,
as absen species wi h he po en ial o es ablish and sp ead could p esen a highe
biosecu i y isk han widesp ead, low-impac species, ye bo h a e ea ed equi a-
len ly unde cu en ules.
To add ess his secu i y isk, he CFIA could conside in oducing a sepa a e
classi ica ion o absen species de ec ed in impo ed seed lo s, unde which a seed
lo could be empo a ily es ic ed un il he species is iden i ied and a p elimina y
isk iage is comple ed. This would no equi e a ull pes isk assessmen p io
o elease bu could ins ead ely on a apid sc eening p o ocol used in weed isk
assessmen amewo ks (Downey e al. 2010), which would e alua e key ac o s
such as he species’ global dis ibu ion, known in asi eness, and po en ial clima ic
sui abili y in Canada. Whe e ini ial isk appea s low, he seed lo could ei he be
eleased as is o condi ionally eleased wi h pos -en y moni o ing. Whe e isk is
po en ially high, he seed lo could be held pending u he assessmen , e-cleaned,
o e u ned o he expo e . These app oaches would help balance ade con inui y
wi h Canada’s biosecu i y objec i es.
Cu en ly, o he CFIA noxious weed classes, only species classi ied as Class
1 noxious weeds a e explici ly p ohibi ed om en e ing Canada in a seed lo .
Al hough his class includes some species no ye p esen in Canada, i emains lim-
i ed in scope, comp ising jus 25 species and one genus (Cuscu a spp.), and has no
been upda ed since he mos ecen e ision o he WSO in 2016 (CFIA 2016b).
Adding o emo ing species om his lis equi es a o mal egula o y amendmen
ollowing s akeholde consul a ion, a p ocess ha can ake se e al yea s; he p e i-
ous upda e occu ed in 2005. The “Plan P o ec ion Ac ” au ho ises he CFIA o
p e en he impo a ion and sp ead o ha m ul plan pes s and may o e a mo e
esponsi e mechanism han he WSO o add essing eme ging biosecu i y h ea s.
Howe e , i appea s o ha e been used in equen ly o egula e weeds, wi h only
i e plan species publicly documen ed as added since 2008 (CFIA 1990, 2024b).
In p ac ice, he Ac is mo e commonly applied o insec s and plan pa hogens. The
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Jesse M. Rubens ein e al.: Biosecu i y isks om weed seeds in impo ed c op seed o Canada
mos ecen publicly documen ed weed addi ion occu ed in 2017, when A undo
donax (gian eed) was added o he lis o egula ed pes s (CFIA 2017a).
A mo e luid amewo k o upda ing Canada’s lis o en y-p ohibi ed species
may be wa an ed o be e add ess conce ns ela ed o no el o absen species wi h
he po en ial o es ablish. New Zealand p esen s a ele an example, wi h i s Min-
is y o P ima y Indus ies main aining a qua an ine weed lis o mo e han 1,700
species p ohibi ed om en y (MPI 2022). This lis is suppo ed by hei “Eme g-
ing Risks Sys em”, which allows o eal- ime upda es in o med by new scien i ic
li e a u e, in e na ional biosecu i y ale s, and submissions om indus y and he
public (Bocks uck 2025). While New Zealand’s smalle egula o y scale and lowe
olume o seed impo s may make such a sys em easie o implemen , elemen s o
his app oach could help in o m imp o emen s o Canada’s amewo k.
Mos common absen species: T i olium esiculosum
A no able example o an absen species ha may wa an close a en ion is
T i olium esiculosum (a owlea clo e ), he mos equen ly epo ed absen spe-
cies in he da ase and na i e o he Medi e anean. I was de ec ed in o age c op
seed lo s o T i olium p a ense ( ed clo e ) and T i olium epens (whi e clo e ). This
con amina ion pa e n aligns wi h p e ious indings showing ha clo e c ops a e
o en con amina ed by o he T i olium species (Rubens ein e al. 2021). Such con-
amina ion is acili a ed by he mo phological simila i y be ween he c op and con-
aminan , which complica es mechanical cleaning and limi s he bicide op ions, as
chemis y a ge ing he weed would also damage he c op (Rubens ein e al. 2023).
While T. esiculosum is no cu en ly cul i a ed in Canada, i is widely used in
pas u e and co e c op seed mix u es in wa me egions o he USA (Pembe on e
al. 1998). Al hough no ypically conside ed in asi e, he CFIA ecen ly iden i ied
T. esiculosum as a po en ial phy osani a y isk in a p elimina y weed isk analysis
(CFIA 2025b). I s epea ed de ec ion in seed lo s, along wi h o he equen ly
epo ed absen species, aises conce ns abou po en ial es ablishmen , pa icula ly
gi en i s ongoing cul i a ion in a neighbou ing coun y and he possibili y ha
clima e change could expand i s sui able habi a in Canada.
Clima ic o e lap and es ablishmen po en ial o absen species
This isk o es ablishmen is pa icula ly ele an in egions whe e Canadian and
USA clima es o e lap. Se e al o he epo ed con aminan species classi ied as ab-
sen om Canada a e al eady es ablished in nea by USA egions. Fo example,
T i olium hi um ( ose clo e ) is a well-es ablished in oduced weed in no he n
Cali o nia and is conside ed in asi e in pa s o i s in oduced ange (iNa u alis
2025c). To ilis nodosa (kno ed hedge-pa sley) and Galium pa isiense (wall bed-
s aw) a e bo h widesp ead in oduced weeds in he Paci ic No hwes and eas -
e n USA (iNa u alis 2025a, 2025b). Thei p esence in clima ically simila a eas
unde sco es he po en ial o es ablishmen in Canadian p o inces such as B i ish
Columbia, a key egion o c op seed p oduc ion.
While absen species epo ed as seed lo con aminan s aise biosecu i y con-
ce ns, hei classi ica ion alone does no always imply high es ablishmen isk.
Many may be poo ly sui ed o Canadian condi ions, such as egions wi h long
win e s, o may be associa ed wi h c op ypes a ely g own domes ically (Wilson e
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Jesse M. Rubens ein e al.: Biosecu i y isks om weed seeds in impo ed c op seed o Canada
al. 2016). S ill, documen ing hese species in impo ed seed lo s emains impo an
o biosecu i y moni o ing and should be conside ed alongside o he isk ac o s,
including clima ic sui abili y and de ec ion equency.
In oduced species wi h he po en ial o sp ead
In addi ion o absen species, eigh con aminan species we e eco ded as in o-
duced, bu only in a single Canadian p o ince. These species may p esen e en
g ea e conce n, as hey ha e al eady demons a ed an abili y o es ablish unde
Canadian condi ions. I is likely ha simila clima es in neighbou ing p o inces
could suppo hei sp ead, po en ially esul ing in b oade ecological and eco-
nomic consequences. The mos equen ly epo ed among hese eigh species was
Ape a spica- en i (silky ben g ass), a g ass weed in oduced in On a io (Desme
and B ouille 2013). I was epo ed in 28 seed lo s o Poa p a ensis (Ken ucky
blueg ass), wo lo s o Poa i ialis ( ough blueg ass), and one lo o Ag os is gi-
gan ea ( ed op). I s epea ed appea ance in g ass seed lo s sugges s a consis en in-
oduc ion pa hway and unde sco es he need o close egula o y sc u iny. As
wi h T i olium species discussed p io , g ass con aminan s such as Ape a spica- en i
a e di icul o emo e mechanically om g ass seed due o hei simila mo pholo-
gy, and selec i e he bicide op ions a e limi ed, as ea men s ha a ge g ass weeds
o en also damage he c op. Al hough no cu en ly he bicide- esis an in Canada,
A. spica- en i has e ol ed esis ance in mo e han ele en Eu opean coun ies, mos
o which expo seed o Canada (Heap 2025). I s esis ance spans mul iple modes
o ac ion, making i challenging and cos ly o manage once es ablished. I has also
been iden i ied as a high- isk candida e o u u e esis ance in New Zealand, whe e
i is equen ly epo ed in seed lo s (Hulme 2024). Gi en ha New Zealand’s
empe a e c opping sys ems and ag onomic p ac ices esemble hose in Canada, i s
expe ience o e s a cau iona y example o he isks o es ablishmen and esis ance.
So ghum halepense (Johnson g ass) is ano he case o conce n. I has only been
epo ed in one Canadian p o ince, On a io (Desme and B ouille 2013), and
in he CFIA da a was epo ed in seed lo s o So ghum × d ummondii (Sudan
g ass). Classi ied as a Class 2 – P ima y noxious weed, i is no ye conside ed o
be occupying i s ull ecological ange in Canada (CFIA 2011). Globally, S. halep-
ense is ecognised as one o he wo ld’s wo s weeds, anking among he en mos
oublesome species (Holm e al. 1997). I has e ol ed he bicide esis ance in o e
a dozen coun ies, including he USA, hough no esis an popula ions ha e ye
been con i med in Canada (Heap 2025). An agg essi e pe ennial ha sp eads by
bo h seed and hizomes, i is no o iously di icul o con ol once es ablished. I s
de ec ion in seed impo s highligh s he impo ance o ea ly iden i ica ion and
a ge ed egula o y ac ion o p e en u he sp ead.
Mos widesp ead gene al weed: Chenopodium album
While he majo i y o con aminan species we e de ec ed in only one o wo c op
species, some weeds appea ed ac oss a b oade ange. Mos no ably, Chenopodium
album (common lamb’s qua e s), an in oduced species in Canada, was epo ed in
seed lo s o 22 di e en c op species, making i he mos widesp ead gene al weed
in he da ase . This is conce ning gi en i s global epu a ion as a pe sis en and
he bicide- esis an weed in seed p oduc ion sys ems (Hulme 2024). Rubens ein
21
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Jesse M. Rubens ein e al.: Biosecu i y isks om weed seeds in impo ed c op seed o Canada
e al. (2021) ound C. album o be he mos equen ly epo ed con aminan in
an analysis o o e 42,000 seed lo s ep esen ing 1,400 c op species impo ed in o
New Zealand. Simila pa e ns ha e been obse ed elsewhe e: i was he mos com-
mon weed in T i olium p a ense ( ed clo e ) seed lo s impo ed in o India (Singh
e al. 2010) and in g ain seed shipmen s en e ing Japan (Ikeda e al. 2022). I s
widesp ead pe sis ence is likely due o i s ecological adap abili y and abili y o
e ade pos -eme gence he bicide applica ions by ge mina ing la e in he c op cycle,
allowing e en la e-eme ging indi iduals o ma u e and p oduce seed (Williams
1963; Rubens ein e al. 2021). In Canada, C. album is al eady ecognised as he -
bicide- esis an in i e p o inces, and globally i has e ol ed esis ance in 20 o he
coun ies, including mul iple cases in he USA (Heap 2025). Al hough al eady
widesp ead, con inued moni o ing is impo an o de ec he in oduc ion o esis-
an bio ypes in o p o inces whe e esis ance has no ye been eco ded.
Eme ging he bicide- esis an weed isks om impo ed seed
On a e age, 9% o he con aminan species (15 species) epo ed each yea we e
known o be he bicide- esis an weeds in he USA bu had no ye been epo ed
as such in Canada. This p opo ion inc eased signi ican ly o e he s udy pe iod.
These indings sugges a g owing isk o new he bicide- esis an weed bio ypes be-
ing in oduced in o Canada ia he impo ed c op seed pa hway. Se e al con am-
inan species highligh ed ea lie in his discussion all in o his ca ego y, including
So ghum halepense and Poa annua, which a e no cu en ly ecognised as HR weeds
in Canada bu a e in he USA (Heap 2025).
O pa icula conce n a e ou species ha we e de ec ed as con aminan s in he
same c op ypes in bo h Canada and he USA. Fo example, Poa annua was ound
in o age and u seed lo s en e ing Canada, and i has also p e iously been epo -
ed as HR in a weedy con ex in hose same c op ypes in he USA (Heap 2025).
Simila pa e ns we e obse ed o Lolium pe enne, Secale ce eale, and So ghum bi-
colo , all o which we e epo ed as Canadian seed lo con aminan s in u , a able,
and o age c ops, espec i ely. All ha e also been documen ed as he bicide- esis-
an weeds in he same c op ypes in he USA (Heap 2025). The biosecu i y isk
is heigh ened by he ac ha some o hese species a e also cul i a ed as c ops in
bo h coun ies, inc easing he likelihood ha esis an bio ypes could es ablish and
sp ead. These cases illus a e a clea pa hway o he in oduc ion o esis an weeds
in o Canadian ag oecosys ems.
Fac o s in luencing he bicide esis ance pa e ns
Se e al ac o s discussed by B unha o e al. (2022) help explain why ce ain weed
species a e he bicide- esis an (HR) in he USA bu no in Canada. In he USA,
widesp ead adop ion o glyphosa e- esis an (GR) c ops, pa icula ly soybean,
maize, and co on, has led o simpli ied weed con ol p og ammes ha ely on
a single o limi ed numbe o he bicide si es o ac ion (SOAs). This has placed
s ong selec ion p essu e on weed popula ions, con ibu ing o he e olu ion and
sp ead o GR weeds. In con as , Canadian c opping sys ems mo e o en include a
b oade di e si y o HR ai s and c op ypes, which likely con ibu es o he slow-
e de elopmen o esis ance. B unha o e al. (2022) also no e ha mo e di e se
c op o a ions, common in he Canadian P ai ies, inco po a e a wide ange o
22
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Jesse M. Rubens ein e al.: Biosecu i y isks om weed seeds in impo ed c op seed o Canada
c ops and he bicide SOAs and ha e been associa ed wi h lowe GR weed p essu e.
By compa ison, simpli ied maize–soybean o a ions a e common in he USA and
linked o highe HR weed equencies. These con as ing pa e ns highligh he
impo ance o o a ional and he bicide di e si y in managing esis ance. O he
con ibu ing ac o s may include di e ences in clima e, speci ic he bicides used,
and na ional app oaches o esis ance moni o ing and epo ing.
He bicide- esis an species wi h po en ial o u he domes ic sp ead
In addi ion, an a e age o 12% o con aminan species epo ed annually in he
CFIA da ase we e al eady he bicide- esis an weeds in bo h he USA and a leas
one Canadian p o ince. Gi en he wide geog aphic dis ibu ion o hese species in
No h Ame ica and hei cu en p esence in Canada, hei con inued de ec ion
in impo ed seed lo s inc eases he isk o esis ance ai s sp eading o addi ional
Canadian p o inces. This g oup includes se e al p oblema ic weeds, such as Echi-
nochloa c us-galli and B omus ec o um, which ha e bo h only been epo ed as
he bicide- esis an weeds in On a io (Guo e al. 2017; Heap 2025).
Ano he no able example is Se a ia i idis, which was among he mos wide-
sp ead gene al weeds in impo ed seed lo s, epo ed in en di e en c op species.
I s inclusion is wo h men ioning, as S. i idis anks as he hi d mos equen ly
epo ed he bicide- esis an weed species in Canada, and esis an bio ypes ha e
al eady been de ec ed in ou p o inces (Heap 2025).
Seed cha ac e is ics in luencing seed lo con amina ion
Unde s anding how seed cha ac e is ics in luence seed lo con amina ion helps
cla i y b oade pa e ns ac oss c op ypes. The absence o a signi ican co ela ion
be ween inspec ion equency and con amina ion a es (Spea man’s co ela ion,
p = 0.560) sugges s ha ac o s aside om equency o inspec ion play a mo e
impo an ole. Fo example, al hough Zea mays (maize) was he mos equen -
ly inspec ed c op, i had he lowes con amina ion a e. In pa , his low a e o
con amina ion is ela ed o he e iciency o cleaning la ge-seeded a able c ops like
Z. mays, whe e p onounced di e ences in size and weigh make weed seeds easie
o emo e (Wych 1988; Wilson e al. 2016; Ge illa e al. 2019). In con as ,
smalle -seeded o age and u c ops a e mo e di icul o clean and end o show
highe con amina ion a es (Rubens ein e al. 2021; Buddenhagen e al. 2022). In
he CFIA da ase , T i olium epens (whi e clo e ), a o age c op, had he highes
con amina ion a e among equen ly inspec ed species. These esul s a e consis-
en wi h indings om New Zealand, whe e impo ed seed lo s o T i olium spe-
cies we e among he mos equen ly con amina ed, while la ge-seeded c ops like
Z. mays had he lowes a es (Rubens ein e al. 2021).
Eme ging echnologies o seed lo inspec ion
Ad ances in biosecu i y echnology a e beginning o add ess some o he limi a-
ions o adi ional inspec ion by p o iding ools ha educe inancial and labou
demands while enabling b oade , mo e e icien su eillance. Fo example, machine
lea ning combined wi h au oma ed imaging sys ems can apidly and consis en ly
iden i y weed seeds based on ex e nal ai s such as colou , e lec ance pa e ns,
23
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Jesse M. Rubens ein e al.: Biosecu i y isks om weed seeds in impo ed c op seed o Canada
shape, size, and ex u e. Recen ly, he CFIA es ed deep lea ning models using RGB
and mul ispec al imaging o seed lo pu i y analysis and epo ed up o 95% ac-
cu acy in iden i ying common weed seeds (Wang 2025). These esul s demons a e
he p ac ical iabili y o such sys ems in egula o y se ings, pa icula ly as aining
da ase s expand o include new species, imp o ing model pe o mance o e ime.
Technologies such as 3D X- ay compu ed omog aphy o e an addi ional ad-
ance by cap u ing bo h ex e nal and in e nal seed mo phology, a he han elying
solely on su ace ai s. High- esolu ion 3D image y can be used o ain a i icial
in elligence models capable o dis inguishing c op and con aminan seeds based
on shape, densi y, biomass, and in e nal s uc u e, all wi hin a closed con aine .
Because X- ay scanning is non-in asi e, seed samples can be p ocessed in sealed
con aine s wi hin minu es and e u ned o he lo , educing eliance on manual
inspec ion (Wol 2025).
Addi ionally, DNA ba coding and o he molecula diagnos ic ools p o ide an-
o he laye o p ecision, enabling species-le el iden i ica ion e en when ex e nal
ai s a e ambiguous o seeds a e physically damaged (James e al. 2014; Le siou e
al. 2024). Toge he , hese echnological ad ances could p o ide a scalable means o
s eng hening seed lo biosecu i y as hey become mo e accessible and a o dable,
while educing bu dens on shippe s and egula o y agencies.
Conclusion
P omising biosecu i y ends iden i ied in his s udy included a signi ican decline
in gene al weeds, a decline in noxious weeds o e ime, a signi ican ly lowe e-
quency o noxious weeds ela i e o non-noxious species, he a e occu ence o
en y-p ohibi ed species, and he ac ha mos con aminan s we e associa ed wi h
only one o wo c op species. Collec i ely, hese ou comes sugges ha egula o y
o e sigh and b oade indus y p ac ices ha e been e ec i e. Howe e , conce ns e-
main. These include con aminan species no ye eco ded in Canada ha a e ei he
equen ly epo ed (e.g., T i olium esiculosum), ha e been classi ied as h ea s o
ag icul u e o he en i onmen (B omus ca ha icus, Eupho bia aleppica), o exhibi
clima ic o e lap wi h egions o he USA (Galium pa isiense, To ilis nodosa, T i oli-
um hi um). Also o conce n a e in oduced species wi h limi ed bu po en ially ex-
panding dis ibu ions (Ape a spica- en i), gene alis weeds ha a ec a b oad ange
o c op species (Chenopodium album), and equen ly epo ed Class 2 – P ima y
noxious weeds (Ci sium a ense, Con ol ulus a ensis, Elymus epens), which ha e
ye o each hei ull ecological ange in Canada. A u he conce n is he inc ease
in eme ging he bicide- esis an species ha may in oduce new esis ance ai s
in o Canada ia he c op seed ade pa hway (So ghum halepense, Poa annua), as
well as species cu en ly eco ded as esis an in only one Canadian p o ince, indi-
ca ing po en ial o wide sp ead (B omus ec o um, Echinochloa c us-galli). Ano h-
e conce n is he in oduc ion o he bicide esis ance h ough con aminan species
p esen in he same c op ypes in Canada, whe e esis an popula ions a e al eady
documen ed in he USA (Poa annua in o age and u c ops).
Addi ional egula o y conce ns ha may wa an u he a en ion by he CFIA
include he impo a ion o c op species also lis ed as noxious o p oblema ic weeds
(B omus ec o um, Poa annua), he allowance o con aminan species no ye e-
co ded in Canada, which a e cu en ly classi ied as Class 6 (non-noxious), and he
dual classi ica ion o na i e species as en y-p ohibi ed weeds (Cuscu a campes is).
24
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Jesse M. Rubens ein e al.: Biosecu i y isks om weed seeds in impo ed c op seed o Canada
I is wo h no ing ha ou conclusions a e based on he p esence o absence o
con aminan species in a seed lo , no he numbe o weed seeds, as his in o ma ion
was no p o ided o us. None heless, access o seed coun da a would be aluable
o u u e esea ch aimed a assessing p opagule p essu e mo e di ec ly (Rubens ein
e al. 2021; Rubens ein e al. 2023). Al hough i was beyond he scope o his s udy,
such da a, combined wi h in o ma ion on a species’ clima ic sui abili y and i s
known in asi eness elsewhe e, could suppo mo e a ge ed weed isk assessmen s.
Ou analysis excluded con aminan s iden i ied only a he genus o amily le el,
which accoun ed o abou 30% o eco ds. The emaining species-le el iden i ica-
ions ep esen ed nea ly wo- hi ds o he sampling da a, while b oade axonomic
en ies we e omi ed o ensu e accu a e classi ica ion. Species-le el iden i ica ion
was essen ial o de e mine a con aminan ’s noxious weed class (i applicable),
whe he i was a gene al weed, and i s o igin s a us. These a ibu es could no
be eliably assessed wi hou species-le el esolu ion. Gi en hese limi a ions, we
encou age epo ing con aminan s a he highes axonomic esolu ion easible o
imp o e he accu acy and u ili y o u u e isk assessmen s. Howe e , we ecognise
ha species-le el iden i ica ion is o en di icul due o incomple e o ambiguous
mo phological ea u es (James e al. 2014).
Canada’s app oach o andomly sampling a p opo ion o all incoming seed lo s
aims o ensu e compliance wi h impo s anda ds and main ain he o e all quali y
o impo ed seed. In p ac ice, hese moni o ing ac i i ies se e as a o m o quali y
con ol. In con as , New Zealand inspec s e e y seed lo a he bo de , ega dless
o in o ma ion p o ided on he seed analysis ce i ica e o he seed lo , e lec ing
a mo e isk-a e se app oach o biosecu i y (Rubens ein e al. 2021). Howe e , o
a coun y he size o Canada, which ecei es a high olume o seed impo s, pa -
icula ly om he USA, wi h which i sha es a long land bo de , inspec ing e e y
lo is no easible due o he labou equi ed and he cos o inspec ion, no is i
necessa ily wa an ed.
Gi en hese p ac ical cons ain s, se e al impo an ques ions a ise. I inspec ing
e e y seed lo is no easible, wha p opo ion should be sampled o ensu e com-
pliance? Can he p esence o a moni o ing sys em alone de e non-compliance by
signalling o expo e s ha Canada en o ces i s s anda ds? And i esou ces a e lim-
i ed, should inspec ion e o s p io i ise impo ed c ops his o ically associa ed wi h
en y-p ohibi ed weeds, species absen om Canada, o he bicide- esis an weeds,
o some combina ion o hese? Fo example, ou analysis showed ha la ge -seeded
a able c ops such as Zea mays had he lowes con amina ion a es, while small-
e -seeded o age and u c ops such as T i olium epens had he highes . In weighing
all hese conside a ions, i is impo an o s ike a balance be ween educing he isk
o in oducing weeds and a oiding unnecessa y ba ie s o in e na ional seed ade.
The ac o s analysed in his s udy p o ide a p ac ical ounda ion o iden i ying
biosecu i y isks, suppo ing CFIA su eillance p io i ies, and o e ing a model o
o he coun ies o collec and analyse hei own seed impo da a. We highligh key
ends, high- isk con aminan species, and egula o y app oaches ha may wa an
close sc u iny. A he same ime, we acknowledge ha policymake s mus weigh
conse a ion goals, ade obliga ions, and ag icul u al p oduc i i y wi hin exis -
ing egula o y amewo ks. As global c op seed ade con inues o g ow, sus ained
moni o ing o his pa hway will be c i ical o sa egua ding domes ic ag icul u e
and na u al ecosys ems.
25
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Jesse M. Rubens ein e al.: Biosecu i y isks om weed seeds in impo ed c op seed o Canada
Acknowledgemen s
The au ho s hank he CFIA Seed Sec ion (O awa) o g an ing pe mission o
use o icial da a, he CFIA seed inspec o s o collec ing moni o ing samples, and
he CFIA Seed Science and Technology Sec ion (Saska oon) o conduc ing seed
sample analysis and compiling he da a. We also acknowledge S e e Jones, Ka en
Cas o, and Willy D os om he CFIA o hei guidance and suppo . Special
hanks go o Seeds Canada o p o iding access o hei SeedS a Da abase (h ps://
seeds-canada.ca/en/seed- esou ces/seeds a - ool). Las ly, we hank Mu ay Kelly o
PGG W igh son Seeds L d o his aluable assis ance.
Addi ional in o ma ion
Con lic o in e es
The au ho s ha e decla ed ha no compe ing in e es s exis .
E hical s a emen
No e hical s a emen was epo ed.
Use o AI
No use o AI was epo ed.
Funding
This esea ch was unded by he Seed Indus y Resea ch Cen e (h ps://www.si c.co.nz) and Plan
& Food Resea ch L d., h ough he Be e Bo de Biosecu i y esea ch collabo a ion (h ps://www.
b3nz.o g.nz). A icle p ocessing cha ges o his publica ion we e co e ed by Lincoln Uni e si y’s
APC Fund.
Au ho con ibu ions
Concep ualisa ion: Jesse M. Rubens ein, John G. Hamp on, Philip E. Hulme, M. Philip Rols on,
Ch is ophe E. Buddenhagen; Da a cu a ion: Jesse M. Rubens ein; Fo mal analysis: Jesse M. Ruben-
s ein; Funding acquisi ion: John G. Hamp on; Me hodology: Jesse M. Rubens ein, John G. Hamp-
on, Philip E. Hulme; P ojec Adminis a ion: Jesse M. Rubens ein; So wa e: Jesse M. Rubens ein;
Supe ision: John G. Hamp on, Philip E. Hulme, M. Philip Rols on; Valida ion: Jesse M. Ruben-
s ein, John G. Hamp on, Philip E. Hulme; Visualisa ions: Jesse M. Rubens ein, Philip E. Hulme;
W i ing – o iginal d a : Jesse M. Rubens ein; W i ing – e iew and edi ing: Jesse M. Rubens ein,
John G. Hamp on, Philip E. Hulme, Ch is ophe E. Buddenhagen, M. Philip Rols on.
Au ho ORCIDs
Jesse M. Rubens ein h ps://o cid.o g/0000-0001-8027-1617
Philip E. Hulme h ps://o cid.o g/0000-0001-5712-0474
Ch is ophe E. Buddenhagen h ps://o cid.o g/0000-0002-3016-1054
M. Philip Rols on h ps://o cid.o g/0000-0001-6340-0878
John G. Hamp on h ps://o cid.o g/0000-0003-3449-825X
Da a a ailabili y
In o ma ion on all epo ed con aminan species is p o ided in he igu es, ables, and suppo ing
in o ma ion o his pape .
