Volume 57 Number 11 Date 06/21/2012
VARIEGATED CUTWORM - Damage has intensified in alfalfa, corn and soybean fields in all areas of the state. A report from Fond du Lac County states that "uncountable" numbers of larvae were found in soybeans near Ripon and another four-acre field in the Loganville area of Sauk County was reportedly "chewed down to the stems". Based on surveys and anecdotal reports, the areas of highest concentration are in the east-central and central districts, including Fond du Lac and Green Lake counties. Cutworms have also been noted in Adams, Barron, Clark, Columbia, Fond du Lac, Grant, Manitowoc, Marathon, Marquette, Sauk, Waupaca, Waushara and Winnebago counties. Continued scouting is imperative at this time, especially alfalfa regrowth, which is highly attractive to the cutworms.
EUROPEAN CORN BORER - The treatment window for first generation larvae has closed near Beloit, Madison, La Crosse, Sullivan and at other locations where 1,100 degree days (base 50°F) were surpassed as of June 20. Larvae are entering the midribs of corn leaves, although feeding is still mostly confined to the whorls. Insecticidal control remains an option in the southeast, central, east-central and northern counties for another week. Corn and vegetable growers concerned about European corn borer damage should appraise the percentage of infested plants now to determine if control is justified. The larvae will soon bore into the stalks where they are protected from chemical sprays.
JAPANESE BEETLE - Emergence of Japanese beetles has been noted in Dane, Racine and Rock counties. Damage to fruit trees, perennials, nursery stock and field crops can be expected for the next two months throughout most of the state, as far north as Barron County in the northwest and Oconto County in the northeast. Soil-applied systemic insecticide treatments should have been made by now to allow 3-4 weeks for the material to be translocated before the beetles begin feeding.
WESTERN BEAN CUTWORM - The annual flight began this week, with counts of 1-17 moths per trap registered in Adams, Brown, Columbia, Dane, Jackson, Juneau, Monroe, Rock, Waushara and Wood counties. Based on current degree day accumulations, 25% of the moth population is expected to emerge during the next two weeks and the majority (50% emergence) should appear in trap collections by July 15. Oviposition on the flag leaf of corn has started in areas where the adults are active. Scouting for eggs and small larvae is recommended as soon as the first moths are registered.
YELLOW-STRIPED ARMYWORM - Localized populations have been noted in Dane, Dunn, Eau Claire, Grant, Lafayette, Rock, Sauk, Vernon and Waushara counties in the past two weeks. Damage attributed to this caterpillar has not surpassed economic levels thus far, but the combination of armyworms and variegated cutworms could push infestation rates above threshold. Populations of both caterpillars are higher than normal this season.
--Krista Hamilton, DATCP Entomologist