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Rainy and cool weather prevailed for much of the week in Wisconsin. After a warm, dry window May 5-18 allowed farmers to plant approximately half of this year’s intended corn, oat, and soybean crops, fieldwork paused as brisk conditions set in and widespread rain soaked the state. Daytime highs were below normal in the 50s to low 60s, while overnight lows in the lower 30s to around 50 brought frost advisories to the central and northern areas. Weekly precipitation amounts of 0.5 to 2.0 inches were common statewide.
Prior to the wet weather, planting of the 2025 corn crop had reached 73% complete, five days ahead of last year and three days ahead of the five-year average. Soybean planting was also five days ahead of last year and four days ahead of the average before the rain started, at 66% complete (USDA NASS).
Wisconsin farmers are waiting for the return of dry conditions and warmer temperatures to finish planting corn, oats, and potatoes, and to continue harvesting the first alfalfa crop. This week’s inclement weather also delayed the start of the spongy moth aerial treatments to May 22, three days later than scheduled.
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The alfalfa weevil damage season is underway in parts of the state. DATCP alfalfa surveys conducted in the southern counties estimate leaf tip feeding injury is still low at 5-20% throughout sampled fields, but feeding pressure is expected to intensify next week as more larvae transition into the larger and most destructive third and fourth-instar development stages.
The Alfalfa Weevil model offered by the UW-Madison Vegetable Disease & Insect Forecasting Network (VDIFN) estimates where scouting for larvae and damage should be concentrated based on degree day accumulations and anticipated life stages. Red and orange shaded areas, namely in southwestern and south-central Wisconsin, are where scouting is most critical at this time. Degree day accumulations in these high-risk areas range from 400-500 and weevil larvae are reaching the third and fourth instars, when feeding damage is heaviest. Note that a red “very high” risk rating on the map does not necessarily mean severe alfalfa weevil feeding is occurring. It simply indicates larvae are in the development stage where heavy feeding may occur if the weevil population is high in a field. The only way to determine actual alfalfa weevil feeding pressure is to scout fields. |
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In the week ahead (May 25-31), more of the state will enter the orange and red high to very high categories and scouting will be particularly important. The method for assessing alfalfa weevil damage is to collect 50 stems at random from throughout the field, checking each stem for characteristic weevil leaf feeding, and estimating the percent of stems showing defoliation. Management is recommended when 40% of the alfalfa stems have alfalfa weevil feeding and the field is more than seven days from the scheduled harvest date. Lastly, sweeping fields with a standard 15-inch net is helpful for determining the growth stages and abundance of weevil larvae, but the economic threshold is based on percentage of stems showing tip feeding across the field and not the number of larvae collected per sweep.
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Black cutworm larvae from mid-April flights have grown large enough to cut emerging corn plants. A moderate risk of localized black cutworm infestations is forecasted through early to mid-June based on the timing of moth arrivals this spring relative to the start of corn planting, favorable field conditions, and the locally heavy moth counts reported by the Black Cutworm Monitoring Network. As more corn acreage emerges across the state, scouting for signs of black cutworm infestation is strongly advised.
During the week ending May 22, DATCP’s network recorded another influx of black cutworm moths. The 97 survey traps collected 956 moths, for a cumulative total of 3,686 moths since April 1. This spring’s average count of 38 moths per trap has surpassed the 10-year average of 37 moths per trap, but is still below the 72-per-trap average recorded in 2017, the last time serious black cutworm infestations were documented in the state.
Corn acreage that had dense broadleaf weed infestation prior to planting, fields with cover crops that were terminated late, and sites with heavy crop residue—especially corn planted into soybean residue—are at greater risk of infestation and should be routinely checked from emergence though the five-leaf V5 stage. A threshold of 3% cutting of plants (with a range of 2-5%) has traditionally been used as the point at which growers should consider a rescue treatment. Early and timely detection of cutworm infestations is critical for controls to be effective. |
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This week’s cold, wet, and windy weather interrupted the start of the spring codling moth flight. A few cooperators in DATCP’s apple pest monitoring network reported their first moths of the season May 12-14, but chilly temperatures have kept emergence on hold and most orchard sites have not established a biofix as of May 22.
Orchards with a history of high codling moth pressure or a large first flight of more than 10 moths per week usually apply the first larvicide spray at 250 degree days (modified base 50°) after the biofix. Treatments applied at this threshold coincide with 3% hatch of first-generation larvae. However, if the initial flight is light or inconsistent due to cooler temperatures or rain (as is the case for several reporting orchards this season), a stronger flight can occur after the earliest moths appear in traps. In this scenario, the first larvicide spray can be applied at 350 degree days from the initial biofix to coincide with 15% larval hatch, which will eliminate most of the new larvae before they enter fruits.
Questions about timing the codling moth biofix and first-generation control window can be directed to Krista.Hamilton@wisconsin.gov. |
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