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Weeds
Volume 56 Number 20 Date 11/17/2011 VOLUNTEER CORN - More than half of the state's soybean acreage was infested with volunteer corn in 2011 according to the results of an August survey. Examination of 980 fields found volunteer corn in 57% of the soybean sites, a 13% increase from 43% in 2009 when the survey was last conducted. Approximately 26% of the fields were heavily infested with volunteer corn plants, 20% were moderately infested, and 11% had trace levels. These figures confirm that volunteer corn is not being effectively controlled in Wisconsin and may be causing major yield reductions in about one-quarter of soybean fields. HERBICIDE RESISTANT WEEDS - A survey for weed resistance in soybeans was initiated this season. Weed populations in 102 fields were examined and characterized for indicators of resistance, including: density, quantity and diversity of weed species present (above canopy), weed distribution, growth patterns (evenness in height), signs and degree of herbicide injury to existing weeds, and presence of vigorous weeds next to dead individuals. Of the 102 fields evaluated, none had weed populations suspected of being resistant to herbicides. The survey is expected to continue in 2012. INVASIVE WEEDS - Statewide distribution records were collected in 2011 for three highly invasive weeds: poison hemlock, teasel spp., and wild parsnip. A total of 1,996 site observations were made in 62 counties. Baseline survey data is being used to refine existing distribution maps, forecast potential weed distribution, and guide future management programs. As anticipated, wild parsnip was the most common of the species, observed at 23% of surveyed sites, followed by teasel (1%), and poison hemlock (0.2%). Most wild parsnip was noted in the southwest and south-central districts where an average of 44% and 49% of sites were infested, respectively. In the central and northern areas, invasion by wild parsnip was uncommon and only 2-9% of sites were infested. A map depicting the occurrence of wild parsnip is provided below. Surveys for the other two species, teasel and poison hemlock, indicated that distribution is still very limited. Only 16 of the nearly 2,000 sites were infested. Poison hemlock was found at three sites in Crawford, Green and Marathon counties. BIOLOGICAL CONTROL - Biological agents for control of spotted knapweed and leafy spurge were introduced at nearly 200 new locations this year. An estimated 58,000 spotted knapweed weevils (Larinus spp.) were released in July at 147 sites along the Hwy 39/51 corridor from Portage to Wausau, and next to Hwy 22 in Columbia, Marquette and Waushara counties. Another 43,000 leafy spurge agents were introduced in June at 43 sites in 11 counties. The effort was largely funded by the Department of Transportation and carried out by DOT and DNR personnel. The objective of the biological control program is to establish natural enemies of leafy spurge and spotted knapweed for eventual control of these invasive weeds. --Clarissa Hammond, DATCP Weed Scientist 
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