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   Spring weather has finally moderated in Wisconsin, with the extended forecast calling for a stretch of mild temperatures ahead. The return of a drier, more favorable pattern should provide the season’s first real window of opportunity for fieldwork after inconsistent conditions kept most planting activities on hold. At the start of the week, spring tillage was reported as 21 percent complete, four days ahead of last year but five days behind the five-year average. Two percent of the intended corn crop has been planted, two days ahead of last year but eight days behind the average.
Meanwhile, observations from apple growers indicate variation in apple tree phenology ranging from tight cluster in northern Wisconsin to early pink across the southern counties. The most advanced orchards along the Illinois border are reporting first bloom. Apple growers are expressing relief that the damage caused by last week’s cold spell was not widespread and appears to have impacted only the earliest varieties.
The promising early May weather is expected to improve soil conditions and spur fieldwork, gardening, and plant development throughout the state.
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Much like this spring’s erratic weather, the start of spongy moth egg hatch has foiled predictions. Phenology models estimated April 28 as the start date of egg hatch in southern Wisconsin, but hatch was not observed at a Grant County monitoring site until yesterday, May 3. This estimated date is six days ahead of last year (May 9) but a week behind 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 third week of May. 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 10 western Wisconsin counties for spongy moth this year. Control efforts will be focused in areas where populations are still low or beginning to build.
- Btk aerial treatments will be applied starting in mid-May in the following counties: Chippewa, Crawford, Dunn, Grant, La Crosse, Lafayette, and Rusk.
- Mating disruptor aerial treatments will occur from late June to mid-July in these counties: Barron, Chippewa, Crawford, Dunn, Grant, La Crosse, Lafayette, Vernon, and Washburn.
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 an outbreak phase in the state and levels could remain high or increase in 2023. 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 are the most efficient and effective method to delay the impacts associated with spongy moth establishment and outbreaks. To receive up-to-date information on treatment plans:
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The Canadian Corn Pest Coalition (CCPC) recently announced the detection of a suspected Cry1Ab-resistant European corn borer (ECB) population in Nova Scotia.
According to field crops entomologist Tracy Baute, “This finding is concerning, as the ECB populations in the area were previously found to be resistant to Cry1F in Nova Scotia in 2018, which was the first occurrence of field evolved resistance of ECB to any Bt protein in the world. Since then, another ECB population resistant to Cry1F was found in a field in southern Quebec in 2019 and another in Manitoba in 2020. This indicates that ECB is becoming less susceptible to Cry1 proteins as they share similar modes of action against ECB. If ECB can overcome one of them, it is much easier for them to become tolerant to the other Cry1s too.”
In short, the CCPC announcement should be considered an early warning sign of potential ECB resistance development to Cry1Ab and or Cry1A.105 in the Great Lakes region.
Based on this news, Wisconsin agronomists, corn growers, and crop consultants are encouraged to help build awareness of this issue and to report any Bt corn fields with unexpected injury by ECB, including field corn and sweet corn (signs of ECB activity and injury). DATCP may request collections of ECB larvae be sampled from these fields in early fall for bioassay testing to determine if they are resistant. Additional information is available by clicking the button below.
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Black cutworm moths arrived in substantial numbers this week. The DATCP network of 50 pheromone traps collected 567 moths during the reporting period ending May 4 (average of 11.3 per trap). Significant captures were documented at 15 of the 50 sites, with the highest counts recorded in Barron, Chippewa, Dunn, and Rusk counties. A significant capture of nine or more moths in two nights indicates a large flight has occurred and that a corresponding increase in cutworm egg laying can be expected. The first major flight also marks the point to begin counting degree days to forecast the peak seedling corn damage window. From the date of a significant capture, an average of 300 degree days (modified base 50°F) is required for the black cutworm to develop from the egg stage to the damaging fourth-instar larval stage.
The black cutworm migrates northward each spring from overwintering areas near the Gulf of Mexico and Texas. When appropriate weather systems occur, the moths can reach Wisconsin from Texas in only two days. The first moths were recorded in traps on April 8 this spring and the cumulative count as of May 4 is 733 moths. This total is more than two times higher than the 216 moths captured by the same time last year. The latest counts for the state’s 50 trap sites are available each Thursday on the DATCP Black Cutworm page. |
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The Pest Survey Program at DATCP continues detection work for new and emerging invasive plant pests that threaten Wisconsin’s agricultural and natural resources. For the 2023 season, our program is planning a detection survey for two destructive, economically significant vegetable pests: leek moth and swede midge. We are looking for seven more vegetable growers to help with our 2023 survey.
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Leek moth (Acrolepiopsis assectella) is an allium (onion, garlic, and leek) pest and potential new invader that has not yet been found in Wisconsin.
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Swede midge (Contarinia nasturtii) is a pest of brassica crops (broccoli, cabbage, and kale) documented for the first time in the state in 2019.
 This survey is cooperator-driven and will rely on assistance from vegetable growers willing to set and monitor traps from June 1 through August 31. Cooperators will receive two traps per pest, sticky liners, and pheromone lures, along with instructions for setting the traps. The traps are non-toxic, organic compatible and will last for the 12-week survey period. The trap liners and lures will need to be replaced monthly. At the end of the season, cooperators will mail the trap liners back to the DATCP entomologist for screening. There is no cost to participate and no minimum acreage required. If you grow alliums and brassicas and would like to join this pest detection effort, please email Krista Hamilton at krista.hamilton@wisconsin.gov by May 8 with:
- Your name
- Phone number
- Garden, farm or field location (County, address, GPS coordinates if possible)
DATCP will screen and identify all trap samples. Growers will be advised if swede midge or leek moth is detected on their farm or in their garden, but specific field locations and grower information will not otherwise be shared.
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