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Vegetable Lab People

August 8 Vegetable Updates | MSU

August 8, 2018

Central Michigan vegetable update

For pickles, I do not have any confirmed reports of downy mildew in this part of Michigan yet, however, growers are advised to continue downy mildew fungicide spray programs. The disease has been confirmed in Michigan. See: https://veggies.msu.edu/wp-content/uploads/2018/08/DMCucurbitDownyMildewMap_8.7.18.pdf

Harvest of summer squash continues with powdery mildew becoming more prevalent. Read more.

Southwest Michigan vegetable update

Cucurbit downy mildew pressure will remain high for the rest of the season, especially when we get cloudy, cool, windy conditions. A tighter spray schedule with more effective products is advised by Michigan State University Extension. Morning dew conditions will continue to be conducive for powdery mildew spread. Heavy powdery mildew infections will lead to early defoliation, limiting fruit size and quality. Fruit without leaf cover are prone to sunburn which will break down in storage. Unprotected handles will also be affected leaving the pumpkin without a handle. All stages of squash bugs can be easily found.

Watermelon harvest has begun. Read more.

East Michigan vegetable update

Cucurbit downy mildew pressure will remain high for the rest of the season, especially when we get cloudy, cool, windy conditions. A tighter spray schedule with more effective products is advised by Michigan State University Extension. Morning dew conditions will continue to be conducive for powdery mildew spread. Heavy powdery mildew infections will lead to early defoliation, limiting fruit size and quality. Fruit without leaf cover are prone to sunburn which will break down in storage. Unprotected handles will also be affected leaving the pumpkin without a handle. All stages of squash bugs can be easily found.

Watermelon harvest has begun. Read more.

Southeast Michigan vegetable update

In cucumbers and melons, downy mildew reports continue to roll in from other parts of Michigan and neighboring states. Both watermelon and cantaloupe harvest will pick up in the next week.

Winter squash and pumpkins continue to add size and mature. Bacterial leaf spot and powdery mildew are appearing. There are many products available to help control powdery mildew. Pumpkins especially benefit from a good program, as the season is long and powdery mildew can infect the handle and cause it to fall off.

There can sometimes be confusion over identification of powdery mildew vs varietal appearances. Some varieties of winter squash and pumpkins (as well as summer squash and zucchini) have white areas around the veins. This is not a disease, it is just something in the genetics of the variety. Powdery mildew will have more concentrated, pronounced areas on the leaf. You will also see discrete white areas on the bottoms of the leaves.Read more.

West central Michigan vegetable update

In cucurbits, cucurbit downy mildew was detected at additional sites in southwest Michigan as well as in Saginaw and Arenac counties over the last week; it is on the move and cucumbers and melons need to be protected. Orondis Opti has proven most effective for cucurbit downy mildew in trials. Ranman is less effective than Orondis Opti but more effective than other products. Zampro and Elumin are “third-tier” products that may be slightly better than Gavel and Zing, which could also be considered to be in the third tier. Read more in “Downy Mildew found in Michigan cucumbers in 2018” from Michigan State University Extension.

Phytophthora capsici was causing fruit rot and leaf lesions in one zucchini field and root, crown and petiole rot in other fields after last week’s wetter weather. When it sporulates, this disease produces a powdered sugar look on infected fruit that is not “cottony and puffy.” Orondis Ultra (zero-day pre-harvest interval) and Ridomil Gold Bravo (zero-day pre-harvest interval) are “A-team” products for protecting cucurbits—note, there may be Ridomil resistance in areas with a history of using mefenoxam/metalaxyl. Revus (zero-day pre-harvest interval) and Presidio (two-day pre-harvest interval) are “B-team” products. There are other versions of Ridomil, but they have longer pre-harvest intervals, which makes them hard to use in zucchini, but possible for winter squash. Read more.