West central Michigan vegetable regional report – July 15, 2015

Conditions this week and further detections show spread of cucurbit downy mildew remains a significant challenge to area cucumber and melon growers. Downy mildew-specific products need to be applied now.


Asparagus plantings have fully expanded leaves right now. Purple spot was visible on main stems in an established planting high up on the plant this week and on newly planted asparagus. Rust was visible in a new planting as well. New fields adjacent to older fields with a history of rust issues, or bordered by volunteer asparagus, could be at risk for this disease, which can spread via air currents early in the season. Michigan State University Extension plant pathologist Mary Hausbeck recommends protecting new plantings with fungicides. Applications banded over the row can help avoid wasting product where feasible. Chlorothalonil is a good general protectant for purple spot with some rust activity and should be applied. If rust is spotted and is a concern, up to three applications of Tebuconazole-containing products (Orius 3.6F, Tebuzol 3.6F) can be made. Japanese beetle activity has continued this week. Asparagus beetle damage due to larval feeding was visible in a young planting.

Bean fields to our east have been challenged by root rots this year.

Carrot fields have been challenged by weeds in the aster family in some locations, including spotted knapweed and common groundsel. Lorox applications unfortunately only kill emerged groundsel plants when they are small and provide only fair pre-emergence control.

Cole crops in multiple locations, including turnips, radishes and cabbage, have been more challenged by maggot pests this year. This is likely due to cool, wet weather, which is ideal for seedcorn and cabbage maggots. Typically, maggot pests are only a problem early in the season on newly planted transplants -0 when this type of weather is present. However, maggots have also been reported in the last week from ready-to-harvest cabbage heads, with damage to the base of the head.

Cucurbit downy mildew has been confirmed in six Michigan counties to date: Monroe, Gratiot, Allegan, Livingston, Tuscola and Macomb. Disease spread is very rapid and moving more quickly than spore trap counts would suggest. Foliar applications of downy mildew products on a four- to seven-day schedule will have the best chance of limiting impacts of this disease in cucumbers and melons. Normal protectants such as chlorothalonil will not provide protection on their own. Hausbeck gives an example spray program for downy mildew control. Please send photos via email to .(JavaScript must be enabled to view this email address) showing both the tops and bottoms of leaves if you suspect your cucumbers or melons have this disease. A factsheet for home gardeners provides a good general description of this disease.

I observed moths resembling squash vine borers active in a zucchini field this week. If desired, control measures for this pest need to be initiated as soon as it is detected. Applications of a pyrethroid or a Bt product such as Agree can be made weekly during the egglaying period (about three weeks). Limited trials in New York suggest the form of Bt in Agree – the aizawi strain – is more effective than the kurstaki strain for this pest. Product needs to be directed to the base of the plant where eggs are laid. Hatching larvae bore into the plant within hours, so if they do not contact product at this time, they will feed within the vines where they are protected from pesticides.

Onion harvest is drawing closer for transplanted onions and early maturing varieties that were direct sown. Keep an eye out for onion anthracnose in addition to other foliar diseases.

Potato and tomato growers should be aware that conditions have continued to be very conducive for late blight. The closest potential report occurred on tomatoes in western Ontario July 14, however the USA Blight website states samples were not taken. This disease has been reported from western New York, where sampling confirmed presence of this pathogen.

Bacterial speck and spot continue to be present on tomatoes, with reports of poor control with copper. Please let your local MSU Extension vegetable educator know if you suspect you have bacterial pathogens on tomatoes with copper resistance.

Sweet corn growers may notice yellowing corn on lighter texture soils within their fields. This could be due to Nitrogen leaching or denitrification, and is most likely in areas with heavy rains. Consider taking a plant tissue sample prior to pollination to determine if additional nitrogen applications may help boost yields. You can submit samples to the MSU Soil and Plant Nutrient Laboratory or directly to A&L Great Lakes Laboratories. The Nitrate-N test is appropriate. View the guidelines for sampling corn before submitting a sample.

Insect Forecast suggests some risk of corn earworm migration tomorrow, July 16, through this weekend. Checking traps Saturday and Monday will be worthwhile. This is the first forecast I have seen to date suggesting a risk of migration into our region. Western bean cutworm flights should be continuing this week.

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