Volume 63 Number 11 Date 07/12/2018
CORN EARWORM - Twenty-five specimens were captured at six pheromone trap sites in Dane, Dodge, Fond du Lac counties during the last reporting period. The highest individual count was 13 moths near Ripon in Fond du Lac 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.
STRIPED CUCUMBER BEETLE - These yellow beetles with black stripes have been uncommon so far this season. Surveys in 10 community gardens and CSAs in the past week found only a single beetle at a Dane County site. The sampling protocol involved examination of 20 host plants per location. Despite their current scarcity, 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.
LATE BLIGHT - Disease severity value (DSV) accumulations near Grand Marsh, Hancock and Plover have exceeded the late blight risk threshold, indicating that the requirements for disease development have been met in these locations. In the Antigo area, the DSV accumulation is above-threshold for early and mid-plantings, but still below-threshold for later potato plantings. Commercial potato fields infected with this disease have not been confirmed in Wisconsin to date. The closest confirmed reports of potato and tomato late blight are from Pennsylvania. UW-Extension Vegetable Plant Pathologist Dr. Amanda Gevens is advising potato growers to begin routine preventative fungicide applications to protect their crops. Registered fungicides for potato late blight in Wisconsin are provided in the following link: http://www.plantpath.wisc.edu/wivegdis/pdf/2018/2018%20Potato%20Late%20Blight%20Fungicides.pdf
SQUASH BUG - Low numbers of adults and egg clusters were observed at four of 10 vegetable sites sampled from July 5-11. The highest count recorded was four 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 their 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 aggregate 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. Growers should be aware that the smaller nymphs are more readily killed than the adults. Refer to UWEX publication A3422 "Commercial Vegetable Production in Wisconsin" for a list of registered insecticides.
POTATO LEAFHOPPER - Populations in vegetable crops have increased in the past two weeks as a result of drier weather conditions and alfalfa harvest operations. Reports indicate that counts are approaching economic levels 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.
-- Krista Hamilton, DATCP Entomologist