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Rain soaked the state during the first week of June, continuing an above-normal spring precipitation trend in Wisconsin. Seven-day rainfall totals of 4.0 inches or more were recorded in numerous south-central and southeastern locations, with the highest single-day amounts of 2.5-4.0 inches falling June 3. According to the latest Wisconsin Drought Monitor map, the wetter than normal meteorological spring (March 1-May 31) has alleviated carryover drought across nearly the entire state and soil moisture is now adequate to locally excessive for crop lands. In fact, the National Weather Service reports that almost twice the usual amount of early-season rainfall (15.8 inches) has fallen in Milwaukee, where it has been the third wettest spring on record. In Madison, spring 2024 has been the ninth rainiest on record, with 13.1 inches of precipitation for the three-month period.
While the abundant rain has been beneficial in correcting long-term drought and restoring soil moisture reserves needed for crop emergence, persistent wet weather is delaying the first cutting of alfalfa and impeding planting efforts in northern Wisconsin. Planting progress for corn, which had been advancing well ahead of the average much of this spring, has slowed and is now trailing last year by seven days and the five-year average by two days.
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As harvest of first-crop alfalfa continues in between rain showers, surveys in southern Wisconsin are finding low to moderate numbers of variegated cutworm larvae in uncut first-crop fields and in 8 to 12-inch regrowth. The prevalence of the larvae suggests crop scouts and growers statewide should be closely inspecting recently cut stands for this species. Variegated cutworm is a sporadic, migratory pest that last appeared in record numbers in Wisconsin crops in 2012. The caterpillar is distinctive and can be differentiated from other cutworms by a single row of 4-5 yellow circular spots on the back (as shown in the photo above).
Larvae were collected in sweep nets from several fields in Jefferson, Sauk, and Rock counties in the past week, with counts ranging from 1-10 larvae per 100 sweeps. The highest count was recorded in eight-inch alfalfa regrowth in Jefferson County. The larvae observed as of June 4 were in the mid-growth stages (about one inch-long) and will likely continue feeding for another week before reaching full size. A fully grown variegated cutworm larva is about 1.5 to 2.0 inches long.
 Variegated cutworm outbreak in 2012 | Mike Weiss
In addition to the variegated cutworm activity noted in alfalfa, this pest has been identified as the cause of damage to seedling vegetables at many locations in the state since mid-May. DATCP received scattered reports of cutworm feeding on beans, broccoli, cauliflower, potato, and tomato transplants from La Crosse, Richland, Sauk, and Vernon counties. Considered one of the most damaging cutworms, the larvae of this species climb plants at night to feed on foliage and fruits.
Based on recent survey observations and reports, there is potential for variegated cutworm problems to develop in alfalfa, field crops, and gardens this month. For alfalfa, harvesting the first-crop alfalfa as soon as possible is recommended as the first control option. If a field cannot be harvested soon, or where larvae are feeding on second-crop regrowth, the economic threshold is two cutworm larvae per square foot. The larvae are not difficult to find by checking the soil under plant debris and in cracks, and should easily turn up in sweep nets.
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Surveys to assess alfalfa pest populations and distribution are underway. As expected for early June, alfalfa weevil larvae, pea aphids, and plant bugs are currently the most abundant insects in alfalfa sweep net collections. Sampling across Columbia, Dane, Green, Jefferson, Rock, and Sauk counties in south-central Wisconsin indicates alfalfa weevil larval counts range from 0.1-4.8 per sweep. The average is approximately 3.9 larvae per sweep. Estimates of leaf tip feeding were above the 40% economic threshold in over half (55%) of the fields surveyed in the past week, signaling that cutting the first crop should be prioritized for the next rain-free window.
The peak weevil damage period occurs between 600 and 800 degree days (sine base 48°F) in Wisconsin and is in full swing from Madison to Eau Claire, as shown in the DATCP degree-day table. In areas north of Wausau, weevil feeding is likely to intensify in the week ahead (June 7-13) as more weevil grubs enter the most destructive third and fourth instars.
Cutting alfalfa as soon as the weather permits is advised to avoid damage by the larger late-stage weevil larvae. It is also important to note that feeding damage by alfalfa weevil, variegated cutworm, and other pests may still occur under windrows if hay cannot be baled shortly after cutting. Alfalfa regrowth should be checked for signs of weevil injury 4-5 days after harvest and until new growth of the second crop is established. The economic threshold for regrowth is reached if 40% of new stems or crown buds show damage and weevil larvae are still actively feeding in the field. |
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Earlier this spring, the emerald ash borer (EAB) was detected for the first time in Taylor and Washburn counties in northern Wisconsin, bringing the total count of infested counties in the state to 71. Burnett County is the only remaining Wisconsin county where EAB has not yet been confirmed.
The invasive EAB has spread rapidly since 2008 when it was first found in the state, decimating millions of ash trees. In its Forest Health 2023 Annual Report, the Wisconsin DNR estimates that more than 50% of ash trees have been killed in the southern half of the state. In addition, in the 21 most heavily infested southeastern Wisconsin counties and along the Mississippi River south of Pepin County, ash tree mortality is considerably higher at 90%. By contrast, EAB’s full impact still has not been realized in the northern half of Wisconsin where about 25% to 50% of the ash tree population is in decline and the counties where it has been found have only small pockets of infestation. |
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DATCP, DNR, Tribal partners, and UW-Extension all continue to track the spread of EAB in the state and share distribution information through online maps. To see if EAB has been found in your community or to report a potential new detection in an area not yet infested, please visit the interactive Wisconsin EAB Detections map. Additional information and resource links are also available on the DNR EAB web page by clicking the button below. |
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