(Apera spica-venti)

ALS inhibitors (B/2)

Silky Windgrass (Apera spica-venti) is a monocot weed in the Poaceae family.  In Sweden this weed first evolved resistance to Group B/2 herbicides in 2010 and infests Winter wheat.   Group B/2 herbicides are known as ALS inhibitors (Inhibition of Acetolactate Synthase ).  Research has shown that these particular biotypes are resistant to iodosulfuron-methyl-sodium, pyroxsulam, and sulfosulfuron and they may be cross-resistant to other Group B/2 herbicides.

The 'Group' letters/numbers that you see throughout this web site refer to the classification of herbicides by their site of action. To see a full list of herbicides and HRAC herbicide classifications click here.

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QUIK STATS (last updated Sep 29, 2019 )

Common NameSilky Windgrass
SpeciesApera spica-venti
GroupALS inhibitors (B/2)
Herbicidesiodosulfuron-methyl-sodium, pyroxsulam, and sulfosulfuron
Situation(s)Winter wheat
Contributors - (Alphabetically)Rikard Anderson, and Solvejg Mathiassen 
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Henrik Hallquist
Loose Silky-bent (Apera spica venti) and isoproturon (Arelon) resistance surveys in SWEDEN
Exctracts from the final report to the Swedish Board of Agriculture 2006. Development of herbicide resistant weeds in Sweden identification and extent.  Author Liv Åkerblom Espeby and Håkan Fogelfors Swedish University of Agriculture

Materials and Methods
Seeds of Loose Silky-bent were collected in three counties Skåne, Östergötland and Öland 2002. Dose-response experiments were performed in the greenhouse. The susceptibility of field  samples was compared with a sensitive population, a population with enhanced degradation from Switzerland (Delabys and Merimillod, 1999) and a German highly resistant population with unknown mechanism of resistance (Niemann, 2000). Six doses of Arelon  (500 g/L isoproturon) were applied at the 3-5 leaf stage (Table 1).   Table 1. Arelon FL (500 g isoproturon/l) used against
Loose Silky-bent. Treatment Dosage l/ha Dosage % of normal field dose A 0 0 % B 0,06 2 % C 0,15 5 % D 0,3 10 % E 0,75 25 % F 1,50 50 % G 3,00 100 %
For each plant was assessed survival from death to completely unaffected. Aboveground plant parts were harvested, and within each population the relative fresh weight (AVI) of treated plants compared to untreated plants was calculated.

In 24 of the 60 surveyed field samples of  Loose Silky-bent the resistance level to isoproturon was equal to or higher than the Swiss resistant population. In six fields, the incidence was so high that a reduced effect of ispoproturon was very likely in a field situation. The resistance level of the German population was generally higher than the Swedish samples. A few samples (especially in a sample from the county Östergötland) included single plants with an almost equally high resistance as in the German sample. No regional differences were found.

References Delabays, N., and Mermillod, G. 1999. Développement d'un biotest rapide pour confirmer les cas de résistance à l'isoproturon chez le jouet-du-vent Apera spica-venti. Revue suisse Agric. 31, 245-248. Niemann, P. 2000. Resistenz von Windhalm Apera spica-venti gegenüber Isoproturon. Mitt. Biol. Bundesanst. Land-Forstwirtsch. 376, 147-148.

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Henrik Hallquist

Status for resistance in Apera Spica-venti in Sweden and Denmark

Results of surveys in 2010 and 2011 can be found in abstract from Global herbicide resistance challenge (attached). An additional survey was conducted in 2012.

In summary:

2010: 31 samples testet. One population of A. spica-venti from DK showed asignificant lower responses to iodosulfuron, sulfosulfuron and fenoxaprop-P than the susceptible reference indicating ALS resistance with cross resistance to fenoxaprop-P. Resistance was later confirmed in a German test. One population from Sweden showed significant lower response to iodosulfuron and sulfosulfuron but not to fenoxaprop.  2011: 21 samples testet (13 DK, 8 SE). The results indicated resistance to sulfonylureas (iodosulfuron and sulfosulfuron) in 5 field samples (1 DK, 4 SE). One sample was also resistant to fenoxaprop. Two of the populations were from the same farms (but different fields) as the resistant samples in the 2010 survey. 2012: 28 samples testet (15 DK, 13 SE). Four populations (3 DK and 1 SE) were significantly less susceptible to iodosulfuron and sulfosulfuron than the susceptible reference populations indicating a moderate level of resistance. The efficacy of iodosulfuron was significantly reduced at the recommended field dose while the 4 N dose provided full control. The activity of sulfosulfuron was less affected and full control was obtained at the recommended field dose. One of the populations was collected at the same farm where resistance was identified in the 2010 and 2011 tests.

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Henrik Hallquist

First cases of herbicide resistance in Apera spica-venti in Scandinavia


Author(s):Mathiassen S.K.1, Kudsk P.1, Jensen L.S.2

Institution: 1)Department of Agroecology, Aarhus University, Denmark 2) Syngenta Crop Protection, Denmark


An increase in the acreage with winter cereals over the last decades has resulted in severe problems with winter annual grass weeds. Due to a strict pesticide regulation in Sweden and Denmark many residual herbicides are not registered and consequently winter annual grass weeds are controlled mainly by ALS- and ACCase inhibitors causing a high selection pressure on the weed populations. Resistance in Alopecurus myosuroides was first detected in Denmark in 2001 and in Sweden in 2002. Apera spica-venti is another important winter annual grass weed species common in Northern and Central Europe. Herbicide resistant A. spica-venti has previously been found in Germany, Poland, Czech Republic and Switzerland (Heap, 2012). The objective of the present survey was to monitor herbicide resistance in A. spica-venti in Denmark and Sweden. Seeds were sampled in thirty-one fields in 2010 and twenty-one fields in 2011. The susceptibility of the field populations was compared to a susceptible reference population in pot experiments in a glasshouse. Each trial included five herbicides, three (2010) or four doses (2011) and three replicates plus untreated. Foliage fresh weights were recorded four to five weeks after spraying. Prosulfocarb and flurtamone + diflufenican applied at the 1- to 2-leaf stage were highly effective on all populations in both years. Five populations were significantly less susceptible than the reference popuyion to iodosulfuron applied at the 3- to 4-leaf stage. These populations plus another two populations were also significantly less affected by sulfosulfuron. Efficacy of fenoxaprop-P was reduced in two of the seven populations. Our survey revealed that, seven populations had developed resistance to ALS inhibitors 2-,D-10 and that two of the populations were also resistant to ACCase inhibitors indicating multiple 2...6)11 resistance. No cross resistance to thiocarbamates and PDS inhibitors was observed. Heap I. (2012): International survey of herbicide resistant weeds (September 2012)

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Rikard Anderson

In 2017 pyroxulam resistant silky windgrass was found in the county of Blekinge, SE Sweeden.  Four populations from Stubbetorp, Smedjan, Stenborgsgärdet and Smedåkern were resistant to sulfosulfuron and the Stubbetorp population exhibited resistance to pyroxsulam.

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Confirmation Tests

Field, and Greenhouse trials comparing a known susceptible Silky Windgrass biotype with this Silky Windgrass biotype have been used to confirm resistance. For further information on the tests conducted please contact the local weed scientists that provided this information.

Genetic studies on Group B/2 resistant Silky Windgrass have not been reported to the site.  There may be a note below or an article discussing the genetics of this biotype in the Fact Sheets and Other Literature
Mechanism of Resistance

The mechanism of resistance for this biotype is either unknown or has not been entered in the database.  If you know anything about the mechanism of resistance for this biotype then please update the database.
Relative Fitness

There is no record of differences in fitness or competitiveness of these resistant biotypes when compared to that of normal susceptible biotypes.  If you have any information pertaining to the fitness of Group B/2 resistant Silky Windgrass from Sweden please update the database.
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Weed Scientist
Swedish Board of Agriculture
Plant Protection Center
Elevenborgsvägen 4
Alnarp, 230 53 , Skåne County
Email Rikard Anderson
Web   : Web Site Link
Senior Scientist
Aarhus University, Science and Technology
Dept. of Agroecology
P.o. Box 30
Slagelse, 4200, Slagelse Municipality
Email Solvejg Mathiassen
Web   : Web Site Link


The Herbicide Resistance Action Committee, The Weed Science Society of America, and weed scientists in Sweden have been instrumental in providing you this information. Particular thanks is given to Rikard Anderson, and Solvejg Mathiassen for providing detailed information.
Herbicide Resistant Silky Windgrass Globally
(Apera spica-venti)
Herbicide Resistant Silky Windgrass Globally
(Apera spica-venti)
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Herbicide Resistant Silky Windgrass Globally
(Apera spica-venti)
#CountryFirstYearSituationActive IngredientsSite of Action
1 AustriaAustria 2009 Cereals iodosulfuron-methyl-sodium, and isoproturon 2 Multiple Resistance: 2 Sites of Action
ALS inhibitors (B/2)
PSII inhibitors - Serine 264 Binders (C2/7)
20Apera spica-ventiSilky Windgrass6746
2 BelgiumBelgium 2019 Wheat foramsulfuron, iodosulfuron-methyl-sodium, and mesosulfuron-methyl 3 ALS inhibitors (B/2)
20Apera spica-ventiSilky Windgrass18199
3 Czech RepublicCzech Republic 2005 Cereals, and Winter wheat chlorsulfuron, iodosulfuron-methyl-sodium, isoproturon, mesosulfuron-methyl, pyroxsulam, and sulfosulfuron 12 Multiple Resistance: 2 Sites of Action
ALS inhibitors (B/2)
PSII inhibitors - Serine 264 Binders (C2/7)
20Apera spica-ventiSilky Windgrass5266
4 DenmarkDenmark 2011 Winter wheat iodosulfuron-methyl-sodium, and sulfosulfuron 13 ALS inhibitors (B/2)
20Apera spica-ventiSilky Windgrass5674
5 DenmarkDenmark 2016 Wheat fenoxaprop-P-ethyl, florasulam, iodosulfuron-methyl-sodium, mesosulfuron-methyl, and pinoxaden 13 Multiple Resistance: 2 Sites of Action
ACCase inhibitors (A/1)
ALS inhibitors (B/2)
20Apera spica-ventiSilky Windgrass15078
6 FranceFrance 2006 Wheat iodosulfuron-methyl-sodium, mesosulfuron-methyl, and pyroxsulam 17 ALS inhibitors (B/2)
20Apera spica-ventiSilky Windgrass9936
7 GermanyGermany 1997 Cereals, and Winter wheat isoproturon 18 PSII inhibitors - Serine 264 Binders (C2/7)
20Apera spica-ventiSilky Windgrass5026
8 GermanyGermany 2005 Wheat chlorsulfuron, florasulam, flupyrsulfuron-methyl-sodium, iodosulfuron-methyl-sodium, mesosulfuron-methyl, pyroxsulam, sulfometuron-methyl, and sulfosulfuron 18 ALS inhibitors (B/2)
20Apera spica-ventiSilky Windgrass5526
9 GermanyGermany 2009 Spring Barley, and Winter wheat fenoxaprop-P-ethyl, iodosulfuron-methyl-sodium, isoproturon, mesosulfuron-methyl, pinoxaden, pyroxsulam, and sulfosulfuron 18 Multiple Resistance: 3 Sites of Action
ACCase inhibitors (A/1)
ALS inhibitors (B/2)
PSII inhibitors - Serine 264 Binders (C2/7)
20Apera spica-ventiSilky Windgrass5410
10 LatviaLatvia 2015 Wheat, and Winter wheat iodosulfuron-methyl-sodium 174 ALS inhibitors (B/2)
20Apera spica-ventiSilky Windgrass15067
11 LithuaniaLithuania 2013 Winter wheat iodosulfuron-methyl-sodium 185 ALS inhibitors (B/2)
20Apera spica-ventiSilky Windgrass7821
12 PolandPoland 2005 Winter wheat chlorsulfuron, iodosulfuron-methyl-sodium, procarbazone-sodium, and sulfosulfuron 33 ALS inhibitors (B/2)
20Apera spica-ventiSilky Windgrass5395
13 PolandPoland 2010 Winter wheat fenoxaprop-P-ethyl, and pinoxaden 33 ACCase inhibitors (A/1)
20Apera spica-ventiSilky Windgrass5619
14 PolandPoland 2011 Winter wheat chlorsulfuron, fenoxaprop-P-ethyl, pinoxaden, sulfometuron-methyl, and sulfosulfuron 33 Multiple Resistance: 2 Sites of Action
ACCase inhibitors (A/1)
ALS inhibitors (B/2)
20Apera spica-ventiSilky Windgrass6758
15 PolandPoland 2012 Winter wheat isoproturon 33 PSII inhibitors - Serine 264 Binders (C2/7)
20Apera spica-ventiSilky Windgrass6759
16 SwedenSweden 2006 Winter wheat isoproturon 40 PSII inhibitors - Serine 264 Binders (C2/7)
20Apera spica-ventiSilky Windgrass10996
17 SwedenSweden 2010 Winter wheat iodosulfuron-methyl-sodium, pyroxsulam, and sulfosulfuron 40 ALS inhibitors (B/2)
20Apera spica-ventiSilky Windgrass10994
18 SwitzerlandSwitzerland 1994 Wheat isoproturon 41 PSII inhibitors - Serine 264 Binders (C2/7)
20Apera spica-ventiSilky Windgrass208
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PERMISSION MUST BE OBTAINED FIRST if you intend to base a significant portion of a scientific paper on data derived from this site. Citation:
Heap, I.  The International Herbicide-Resistant Weed Database.  Online.  Monday, April 12, 2021 .  Available Copyright © 1993- 2021 All rights reserved. Fair use of this material is encouraged. Proper citation is requested.