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A week of mild weather favored fieldwork across Wisconsin. Afternoon high temperatures in the 50s to mid-70s provided a sustained window of opportunity for spring tillage and planting, while scattered rain improved conditions for crop emergence. According to the USDA National Agricultural Statistics Service (NASS), crop producers continued to make significant planting gains and progress statewide is well ahead of average. Potato planting was 75 percent complete as of April 28, over two weeks ahead of last year and the five-year average. Soybean planting increased nine points during the week to 11 percent complete, nine days ahead of last year’s pace and six days ahead of average.
Recent precipitation has helped improve drought conditions across Wisconsin. Much of the state saw at least a one category improvement in the lingering drought as of the end of April, and the latest NASS crop progress report shows topsoil moisture is currently adequate or surplus for 85 percent of the state’s crop lands.
In southern Wisconsin orchards, most apple tree varieties are in full bloom and pheromone traps have been set in anticipation of the first codling moth flight. Emergence of plum curculio weevils from overwintering sites is also beginning.
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True armyworm pheromone traps are set in Wisconsin each spring to monitor the arrival of migratory moths into the state and to track subsequent flights during the summer months. Similar to the black cutworm, the migratory behavior of true armyworm makes it difficult to forecast where infestations will emerge in the state from year to year. Determining when true armyworm flights are occurring in an area can help growers anticipate when the larvae might appear in their crops. While the number of moths collected in traps cannot forecast true armyworm outbreaks with certainty, the counts may provide an early warning that conditions are suitable for armyworm infestations and inform concentrated scouting windows.
This spring, moth flights have been underway since late March. Trap counts rose noticeably last week (April 18-24) when the network’s traps collected a total of 366 moths, or an average of 17 moths per trap. Another 559 moths were recorded this week (April 25-May 2). As of May 2, the cumulative total true armyworm moth catch is 1,037 moths in 25 traps, or an average of 41 moths per trap.
It is important to note that the primary function of pheromone traps is not to provide definitive data on true armyworm abundance or pressure, but to act as an indicator of moth flight activity and potential egg laying. Crop scouting is required two to three weeks after large flights are recorded to check for larvae and early signs of feeding damage. The recent increase in moth counts at Wisconsin's true armyworm monitoring sites signals that egg laying is occurring in small grains, pastures, and other available grass hosts. First-generation larvae should begin hatching by mid-May.
A summary of weekly true armyworm trap counts is provided on the DATCP true armyworm monitoring network page. Thank you to the many cooperators who have volunteered to maintain pheromone traps throughout Wisconsin this season. Nearby states including Illinois, Indiana, Michigan, and Ohio also report true armyworm trap counts:
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Egg hatch of spongy moth began on April 17 in Walworth County and is underway throughout southern Wisconsin as of April 29. The first hatch date for 2024 is the third earliest on record in Wisconsin and is about two weeks ahead of both last year (May 4) and the 20-year average. Phenological indicators of spongy moth egg hatch include first bloom of eastern redbud and petal-fall of saucer magnolia.
Aerial spray treatments of Bacillus thuringiensis var. kurstaki (Btk) directed against the newly emerged first and second instar spongy moth caterpillars will likely start during the week of May 13. The earliest start date in the more than 30-year history of the Wisconsin spongy moth treatment program was April 26 in 2012, while the latest was May 23 in 2011. DATCP plans to treat sites in nine western Wisconsin counties for spongy moth this year. Control efforts will focus on slowing the spread of spongy moth into areas where populations are still low or beginning to build.
- Btk aerial treatments will be applied starting in mid-May in the following counties: Barron, Buffalo, Chippewa, Crawford, Dunn, Grant, Iowa, Lafayette, and Rusk.
- Mating disruptor aerial treatments will occur from late June to mid-July in these counties: Dunn, Grant, and Lafayette.
Where spongy moth is established in the eastern two-thirds of Wisconsin, it has been a periodic public nuisance and damaging forest pest. Last summer, caterpillar populations reached record levels in the state and it is unclear if the outbreak phase will continue in 2024. Besides noticeable tree defoliation, the harmful effects of spongy moth also include the cost of removing dead trees, potential loss of property value, and irritation of the eyes, skin, and respiratory system in humans caused by the allergenic bristly skins shed by the caterpillars. Aerial treatments targeting newly established and building populations are the most efficient and effective method to delay the impacts associated with spongy moth establishment and outbreaks.
The State of Wisconsin does not offer state-sponsored aerial treatments or a cost sharing program to suppress established populations of spongy moth. Landowners seeking spongy moth management guidance are encouraged to consult resources offered by UW-Extension. The DNR also offers guidelines for homeowner groups interested in organizing their own aerial spray. To receive up-to-date information on treatment plans:
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Cull piles represent a risk to surrounding potato acreage due to the pests and diseases that can survive, overwinter, or build up on the tubers or sprouted plants. Wisconsin potato producers must take steps to dispose of potato cull piles by May 20, 2024, according to ATCP 21.15 Wis. Admin. Code. Cull piles include waste piles of harvested potatoes, seed cutting slivers and waste, storage remnants, and sweepings. The most serious problem associated with cull piles is the late blight pathogen, Phytophthora infestans. The purpose of this regulation is to prevent sprouted overwintered tubers from becoming an early-season source of late blight inoculum. Compliance options for cull pile disposal include:
- Feeding potatoes to livestock so that they are completely consumed by May 20;
- Spreading on fields and incorporating into the soil;
- Depositing the cull potatoes in a licensed landfill with the written permission of the landfill operator;
- Another method that the Department of Agriculture, Trade and Consumer Protection approves in writing.
Growers seeking additional information should contact DATCP potato program coordinator Sara Ott at 608-516-5486 | Sara.Ott@Wisconsin.gov.
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