Volume 63 Number 16 Date 08/23/2018
LATE BLIGHT - Cases of late blight have been confirmed by the UW on commercial potatoes in Adams and Marquette counties. Protective fungicide treatments should be maintained to prevent this disease from developing in tomato and potato crops as harvest continues. Home gardeners, direct marketers and commercial producers who suspect late blight are encouraged to send symptomatic plant material to the UW Plant Disease Diagnostic Clinic: https://pddc.wisc.edu/sample-collection-and-submission/. Late blight testing is free of charge.
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.
CUCURBIT DOWNY MILDEW - This disease was reported in Columbia County on August 17, representing the first case of cucurbit downy mildew (CDM) in the state this season. A 7-day interval fungicide program is advised by UW for cucumber crops when inoculum is likely in the region, narrowing to a 5-day program after disease is confirmed. Leaf samples with CDM symptoms, including angular chlorotic lesions between the leaf veins, should be submitted for diagnosis to the UW Plant Disease Diagnostic Clinic. A map showing the current status of CDM in Wisconsin and the U.S. can be found at the CDM ipmPIPE forecasting site: http://cdm.ipmpipe.org/.
-- Krista Hamilton, DATCP Entomologist