West central Michigan vegetable update – July 25, 2018

Helpful rains came over the weekend, but the change in weather also brought heavier dews, so be on the lookout for foliar diseases.

Rush skeletonweed
Rush skeletonweed develops a long, “leafless” flower stalk from a small, dandelion-like rosette. Clopyralid is the best material available for control of this weed in asparagus and is labelled for pre- or post-harvest use. Photo by Ben Werling, MSU Extension.

In asparagus, there was an uptick in disease severity value accumulation over the weekend at Michigan State University Extension TomCast sensors. Rust uredospores were also visible at one field I visited Monday, July 23. Include tebuconazole in your next cover if rust is detected.

Got rush skeletonweed? This strange-looking plant develops a flowering stalk from a dandelion-like rosette. The stalk has very few leaves and bears yellow flowers. The plant also has milky sap. Spur (active ingredient clopyralid) is likely the best herbicide we have for controlling this weed, and is labelled for pre- and post-harvest applications before fern develops.

In carrots, potential disease symptoms were present in one field I visited this week. Weather over the weekend was conducive to foliar disease development. If you are using the strobilurins Cabrio or Quadris, consider tank-mixing a protectant such as chlorothalonil with them. As we move through the season, remember Merivon and Luna Tranquility are newer materials that can be considered during periods especially favorable for foliar disease.

In cole crops, cabbage looper larvae were present at one field I visited Monday. Cabbage looper larvae are distinct in their movement, they form a loop as they move like inchworms across the plant. They are large, green worms with white stripes, do not have a “velvety” appearance like imported cabbageworm and become much larger than diamondback moth larvae. As noted last week, they have been noted by MSU scouting interns in some parts of the state. If you are an organic grower, consider using spinosad if cabbage looper is the dominant caterpillar. Otherwise, B.t. can provide effective control of diamondback moth and imported cabbage worm.

For cucurbits, cucurbit downy mildew was confirmed in Berrien County cucumbers this week. Pickle, cucumber and melon growers from Muskegon County southward should consider applying a downy mildew-specific fungicide such as Ranman or Zampro. Orondis could be considered if a location has had ample rainfall or irrigation that could increase the risk of problems.

Powdery mildew was reported from a west Michigan pumpkin field this week. Quintec and Torino are two powdery mildew fungicides commonly used in Jack O’ Lantern pumpkins, but there are others as well. Check out the helpful table on page 125 of the Midwest Vegetable Production Guide. It is worth a few minutes of your time as there are a number of options from different modes of action (with different costs).

Onion growers have been concerned about Stemphyllium in recent weeks. Luna Tranquility has proven very effective for this disease in MSU Extension trials. MSU plant pathologist Mary Hausbeck recommends tank-mixing it with a protectant such as chlorothalonil or mancozeb.

For peppers, degree-days suggest the second flight of European corn borer is ongoing. Coragen (active ingredient chlorantraniliprole) and Harvanta (active ingredient cyclaniliprole) are highly effective and selective (i.e., are soft on beneficials that control aphids and thrips). Avaunt and Radiant are other selective products with activity that could be considered for your rotation.

Late blight has not been detected in Michigan potatoes and tomatoes to date.

Corn earworm captures in sweet corn have remained low in Oceana and Kent county traps. However, populations can vary significantly from place to place and moths from earlier flights may be present, so manning your own trap is helpful. Western bean cutworm activity is peaking now. This pest prefers to lay eggs on corn that is just about to tassel. Sprays made for corn earworm typically also take care of this pest. If you want to target it specifically, it could be possible to make an insecticide application at tassel emergence before silking. To scout for this pest, look for egg masses on the upper surfaces of leaves.

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