Root, bulb, leafy and brassica vegetable pest report – 10 July 2012

Threshold for second generation emergence of onion maggot flies has been reached in the Windsor, London, Thedford, Delhi and Bradford/Holland Marsh areas and will be reached in 2-3 days in Wellington. Treatments against adult flies of the second generation are not recommended on dry, cooking or Spanish onions. Degree day accumulations indicate peak of second generation cabbage maggot in Windsor, London, Thedford and Delhi areas. In the Wellington area, this threshold should be reached in 2-3 days. Cabbage maggot control is primarily preventative. The threshold for emergence of first generation carrot rust fly has been reached in Windsor and should be reached in 8-10 days in Thedford and London areas, if resident populations exist.

Aster leafhopper activity has increased in carrots, lettuce and celery in the Holland Marsh. Reports from Michigan State University: Aster leafhopper infectivity remains high inMichigan, ranging from 4.8 to 15.9% depending on the region. The aster yellows index (AYI) is used to determine the need to treat the crop, based on sweep net counts. See OMAFRA’s publication 363, Vegetable Production Recommendations for more information and The Aster Leafhopper and Aster Yellows factsheet.

Purple blotch and stemphylium leaf blight of onions has been seen in the Holland Marsh. See “Update on Stemphylium Leaf Blight of Onions” article for more information. DOWNCAST, which helps predict downy mildew outbreaks in onions, indicated that the risk of downy mildew on transplanted onions and onions with large canopies is moderate to high for the Holland Marsh. DOWNCAST is not available in other areas of Ontario, thus protective fungicides should be applied during cool, humid conditions. Currently, onion downy mildew has not been reported in Ontario.

Here are the degree days accumulated from April 1st until July 10th, 2012.

(These values are provided as guidelines only. Local environments, soil type, field history, etc. may influence activity of these pests.)

*Data provided by Muck Crops Research Station, University of Guelph.

Degree day model information for pests