Volume 57 Number 6 Date 05/17/2012
VARIEGATED CUTWORM - UW-Extension Entomologist Phil Pellitteri reports that there exists a strong potential for outbreaks of this insect in the northern half of the state this spring. He has received several images of cutworm eggs on the windows, eaves and siding of homes in Ashland, Barron, Door, Douglas, Marathon, Oneida and Washburn counties. In addition, the Bayfield County Agent has responded to over 25 calls on the topic and states that eggs have been found on "every house" in Ashland. The larval stages of the variegated cutworm feed on a variety of crops and garden plants, which could spell trouble for growers in these counties next month.
ASTER LEAFHOPPER - Surveys in alfalfa continue to yield moderate to high numbers of this pest. Counts have been comparatively high since the first migrants arrived in April. According to the latest UW-Madison Vegetable Crop Update, testing at the UW-Madison found an 8-12% infectivity rate in the migrant population, indicating that susceptible hosts such as lettuce, carrots and onions are at a moderate risk for aster yellows infection this season. The symptoms of aster yellows disease vary by host but generally include yellowing or chlorosis which progresses to stunting and distortion of the foliage.
Economic thresholds for the aster leafhopper are based on an index calculated by multiplying the percent infectivity by the number of leafhoppers per 100 sweeps (25 sweeps in four locations within a field). The treatment threshold index is 25 for lettuce, 35 for celery and 50-100 for carrots, depending on the variety resistance level.
CABBAGE LOOPER - Migrant moths were registered at the rate of 1-10 per trap for the second week in a row at 10 southwestern Wisconsin locations. Their arrival signals that growers should begin sampling for eggs and small larvae at this time. The yellowish-white, hemispherical eggs are laid singly on the undersides of cabbage, broccoli and cauliflower leaves.
An infestation level of 30% in the cabbage transplant to cupping stage indicates the need for control. The economic threshold for broccoli and cauliflower in the transplant to first flower or curd stage is 50% infestation. If insecticidal treatment is required, it is recommended that growers use a selective material such as Bacillus thuringiensis (Bt).
--Clarissa Hammond, DATCP Pest Survey