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Vegetables
Volume 64 Number 12 Date 07/18/2019


LATE BLIGHT - Development of this disease was confirmed by the UW in a Wood County potato field on July 17. UW-Extension Vegetable Plant Pathologist Dr. Amanda Gevens is advising potato and tomato growers in the Wood County area to maintain routine preventative fungicide applications on a 5 to 7-day schedule to protect their crops. Registered fungicides for potato late blight in Wisconsin are provided in the following link: https://wivegdis.plantpath.wisc.edu/wp-content/uploads/sites/210/2019/06/2019-Potato-Late-Blight-Fungicides.pdf

POTATO LEAFHOPPER - Populations in alfalfa and on some vegetable crops remain very high. Reports indicate that counts are well above-threshold in a few western Wisconsin snap bean plantings. Established economic thresholds are one per sweep or one nymph per 10 leaves in snap beans and three leafhoppers per sweep in potatoes when nymphs are present.

STRIPED CUCUMBER BEETLE - These yellow beetles with black stripes are very common this season. Surveys in community gardens and CSAs in the past week found beetles at nearly all sites, with economic populations noted in Dane and La Crosse counties. Vegetable growers should continue to monitor cucurbits for beetles and signs of bacterial wilt. Control is warranted for populations of one beetle per plant in melons, cucumbers and young pumpkins, and five beetles per plant for less-susceptible cucurbits such as watermelon and squash.

CORN EARWORM - Twenty-two specimens were captured at five pheromone trap sites in Columbia, Dodge, Fond du Lac and Vernon counties during the reporting period ending July 17. The highest individual count was 12 moths at Arlington in Columbia County. The primary migration of moths from the southern U.S. could begin by late July or early August. Participants in the corn earworm trapping network should begin replacing lures on a weekly basis.

SQUASH BUG - Low numbers of adults and egg clusters were observed at several vegetable sites sampled from July 11-17. The highest count recorded was seven egg masses per 20 plants. The treatment threshold for squash bugs is based on an average count of one egg mass per plant, although scouting for tiny eggs is impractical in larger plantings. If the insects are numerous and wilting is observed, chemical control may be considered. For gardens, hand picking and destroying the bugs and the eggs is most effective. Another option is to place cardboard or newspaper on the ground next to the plants. At night, the squash bugs will gather beneath the cardboard and can be destroyed in the morning. Organic growers may use pyrethrum (PyGanic) or the pre-mix with azadirachtin (Azera) directed against the nymphs. Refer to UWEX publication A3422 "Commercial Vegetable Production in Wisconsin" for a list of registered insecticides.

CABBAGE LOOPER - Green to brown frass pellets from the larvae of this pest were observed on cauliflower heads in a La Crosse County CSA garden this week. The larvae were in the intermediate stages. The appearance of the cabbage looper caterpillars suggests that a migration occurred earlier this month, and that increased scouting should begin now and continue through early September. A 10% infestation threshold is suggested from early heading until harvest to protect the market quality of cabbage. The same threshold applies to broccoli and cauliflower once flowers or curds begin to develop.

-- Krista Hamilton, DATCP Entomologist