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Seasonable weather accompanied by rain showers late in the week improved yield prospects for summer crops in Wisconsin. Temperatures were near normal, with highs in the 70s to mid-80s, and most areas of the state received beneficial rain on August 15. Condition ratings for corn and soybeans have shown incremental improvement, by two percentage points each, and 63% of the corn crop and 62% of the state’s soybeans are currently rated as good to excellent. These ratings compare to 55% for corn and 52% for soybeans at the same time last year when much of the state was experiencing moderate to exceptional drought. This month’s timely moisture and lack of extreme heat have supported crop development and harvesting of alfalfa, potatoes, small grains, and sweet corn.
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Wisconsin’s first fall armyworm trapping network is up and running thanks to the collaborative work of DATCP’s Tracy Schilder, UW-Extension Crops and Soils Outreach Specialist Josh Kamps, and 14 volunteer cooperators. This new network is monitoring fall armyworm (FAW) moth flights to provide advanced warning of potential late-season infestations in alfalfa, field corn, sweet corn, and pasture grasses. Although FAW generally arrives too late in fall to cause much damage and historically has not been a major pest in Wisconsin and the upper Midwest, the changing climate and a recent outbreak across the eastern and southern U.S. in 2021 have brought new interest in tracking flights of this migratory insect.
In addition to the moth traps, DATCP’s crop scouts are also looking for FAW and other corn ear-feeding larvae during this month’s corn rootworm beetle survey. Fall armyworm caterpillars have been observed in a few fields in Columbia, Dane, and Green counties, emphasizing the importance of scouting and accurate identification. The striped larvae grow to 1.5 inches long and can be differentiated from other caterpillars found in corn ears at this time of year (i.e., corn earworm, European corn borer, and western bean cutworm) by a conspicuous white, inverted Y-shaped suture on the front of the head capsule and by a set of four black dots arranged in a square on the second to last abdominal segment. |
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 Fall armyworm larva close-up | John Obermeyer Purdue
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As of August 15, the 37 pheromone traps in 18 counties have captured 1,302 fall armyworm moths, or an average of 35 moths per trap. A total of 649 moths were collected this week (August 9-15). The highest individual weekly count is 144 moths in the trap near Arlington in Columbia County. The increase in moth activity this month suggests egg laying is underway in later-planted corn fields. |
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DATCP’s annual corn rootworm beetle survey began August 1 and has reached the halfway point. Counts in the 114 grain corn fields sampled so far have been mostly low, with 88 fields averaging low counts of 0.0-0.4 beetles per plant and six sites having moderate beetle counts in the range of 0.5-0.7 per plant. Above-threshold averages of 0.75 or more beetles per plant have been observed at 20 of the sites as of August 15, primarily in the southwest and south-central counties. The 2024 running average of 0.6 beetle per plant compares to 0.5 beetle per plant at this time last season.
Although early indications suggest that rootworm pressure may be similar to 2023 levels, the survey is only partially complete and beetle emergence has not yet peaked in all areas of the state. Corn producers should be aware of the potential for corn rootworm adults to redistribute from earlier silking fields to later-planted fields as beetle emergence continues. Now is the time to scout to determine this season’s beetle pressure and forecast the risk of larval root injury to continuous corn in 2025. DATCP’s survey includes 230 cornfields and is scheduled to be finished by the end of the month. |
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The western bean cutworm flight is subsiding at northern pheromone trap monitoring locations. As of August 15, the state total count is 15,612 moths in 69 traps (226 per trap average), which surpasses the 9,351 moths in 42 traps (223 per trap average) collected last year and is the highest state average count since Wisconsin western bean cutworm trapping surveys began in 2005.
The highest individual count for the season was 1,095 moths in a Marinette County trap, while nearly one-third of the sites recorded cumulative counts above 250 moths per trap for the season. With 69 trap locations throughout 30 counties, this year’s impressive survey effort has helped identify high moth count areas in the northwestern and northeastern regions of the state (see DATCP survey maps), beyond the traditional high-pressure zone in central Wisconsin. Localized heavy larval populations are anticipated for susceptible corn fields in these areas based on the very high moth counts recorded in late July and August.
All western bean cutworm traps may be removed at this time. The DATCP Pest Survey Program wishes to extend its appreciation to all the volunteers who monitored traps again in 2024. THANK YOU to our cooperators for making this survey possible.
For regional western bean cutworm flight data extending across the northeastern U.S. and adjacent Canadian provinces, please see the Great Lakes and Maritimes Pest Monitoring Network (select WBC tab). |
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A new invasive insect was recently detected in central Wisconsin by one of DATCP’s forest entomologists. The elm zigzag sawfly (Aproceros leucopoda) was observed on elm trees in Portage County last month. This unexpected discovery marked the first confirmed case of the elm pest in Wisconsin and a new state record. Official confirmation was made by USDA-APHIS on July 30, 2024.
Native to East Asia, the elm zigzag sawfly (EZS) was first found in North America in Canada in 2020 and has since spread to several eastern and Midwestern states in the U.S. Its capacity to produce multiple generations each season, in combination with hitchhiking on vehicles, plants, and other outdoor items, has allowed EZS to spread rapidly. Since first observed in Portage County, additional EZS finds have been reported in Adams, Brown, Dane, Jackson, Kenosha, La Crosse, Marquette, Milwaukee, Ozaukee, Pierce, Portage, Rock, Sauk, Sheboygan, St. Croix, Washington, Waukesha, Waupaca and Winnebago counties. The rapidly growing list of positive counties suggests it is established and widely distributed in Wisconsin.
Elm zigzag sawfly feeds on the leaves of any elm species, leaving a distinctive zigzag pattern. Severe defoliation may lead to branch dieback, but direct tree mortality is unlikely. While most healthy trees can recover, many elms are already in decline due to Dutch elm disease and other pests and diseases, so the potential impact of this pest on Wisconsin’s forests is unknown.
There are no planned federal or state quarantines for EZS. The UW-Madison Extension Elm Zigzag Sawfly website offers more information about this new pest and its management. Additional questions or observations on EZS can be sent to datcppesthotline@wisconsin.gov. |
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