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.

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

INTERNATIONAL CONFERENCE 18-22 FEBRUARY 2013 • PERTH AUSTRALIA

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

Email solvejg.mathiassen@agrsci.dk

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 http://www.weedscience.org (September 2012)

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.