Volume 64 Number 17 Date 08/22/2019
LATE BLIGHT - Cases of late blight have been confirmed by the UW in Adams, La Crosse, Monroe, Portage, Vernon, Waushara and Wood counties as of August 20. The western Wisconsin cases (La Crosse, Monroe, and Vernon counties) were diagnosed on tomato samples, whereas the central Wisconsin late blight was found in potatoes. According to UW-Madison Vegetable Plant Pathologist Dr. Amanda Gevens, it is critical that susceptible potatoes and tomatoes in close proximity to the counties listed above be treated with a combination of antisporulant and protectant fungicides to limit reproduction of the pathogen and new infections. Antisporulants include: Orondis, Forum, Curzate, Tanos, Ariston, Previcur, Revus, and Ridomil. All Wisconsin samples tested to date are of the US-23 genotype which can be managed with phenylamide fungicides such as mefenoxam and metalaxyl. A list of late blight fungicides registered for use in Wisconsin is available at: https://wivegdis.wiscweb.wisc.edu/wp-content/uploads/sites/210/2019/06/2019-Potato-Late-Blight-Fungicides.pdf.
SQUASH BUG - Egg deposition is still underway on squash in home gardens. Adults and nymphs are likely to continue feeding on ripening vine crops throughout fall. Chemical control of squash bugs becomes less useful late in the growing season as fruits mature, whereas cultural controls such as removing plant debris around the garden gain importance and are critical for eliminating winter hibernation sites. Crop rotation is also suggested to reduce habitat for the overwintering adult population, which can survive the winter months under plant debris and cause damage to transplants and seedlings next spring.
ONION MAGGOT - Third-generation flies have begun emerging in southeastern and central Wisconsin. Larvae resulting from this final generation of the season will overwinter in cull onions or bulbs left behind in fields. Destruction of crop debris and removal of culls from the field or garden are basic cultural controls. Rotation to a non-host crop should also be considered in spring of 2019 for onion fields or plantings that had onion maggot problems this summer.
-- Krista Hamilton, DATCP Entomologist