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Weekly Fruit Update - May 18, 2022

Capturing Zestar! bloom on 5/17/22.

Author: Annie Klodd, Extension Educator - Fruit and Vegetable Production .


Bloom status was checked in Minnetrista, MN on Tuesday, May 17.

Multiple varieties including SweeTango, Zestar!, and Honeygold were between king bloom to full bloom. Honeycrisp was at pink.

There is a likely apple scab infection event this week, with several rainfalls from Tuesday night through Friday morning. More rain is possible in some places over the weekend. A protectant like manzate sprayed prior to a rainfall will of course help get through an infection event (however, see pollinator safety note below). But if you emitted that application, applying a curative such as Aprovia or Sovran within 3 days (72 hours) post-rainfall will control the existing infection. Waiting longer than 3 days post-rainfall reduces the efficacy of the chemical on the pathogen.

Fungicides and pollinators: While evidence is clear that many insecticides, including organic insecticides, are fatal to bees if applied when they are foraging, almost all fungicides are considered "low" or "very low" risk to bees. There are a few special cases in which certain fungicides in combination with other products have been found to elevate toxicity. Penn State University recommends avoiding Captan, mancozeb, and chlorothalonil (Bravo) during bloom, but considers others to be generally safe. Read this article from Penn State University for more information. 

Of course, those who wish to completely minimize risk to pollinators can avoid use of any pesticides altogether during this time; however, growers should weigh this against the potential apple scab infection that may occur if fungicides are emitted during a rainy period in bloom.


Grapevine at bud break in Minnetrista, MN 5/17/22

Grapes are at or past bud break now, with shoots ranging from 1 inch to 4 inches. Growers should schedule in time now to shoot thin. Complete shoot thinning before the shoots are 11 inches - they can be removed easily by hand when they are small. Since shoots grow rapidly during this time, it is best to begin thinning as soon as possible. If the optimal window is missed, shoots can still be removed but will require pruning sheers. A general rule of thumb is to thin to 2 shoots per spur or 6-7 shoots per linear foot of cordon.

Bud break to bloom is an important time for disease prevention in grapevines. While we can't yet see the diseases, this is the time when many of the fungal pathogens are spreading on the plants. Use the Midwest Fruit Pest Management Guide to guide your spray decisions. In general, preventatives like mancozeb and Captan should be sprayed shortly before a rain to protect the leaves from infection, and curatives should be applied shortly after a rain to control infection that occurred if a preventative application was not done. 


As strawberries approach bloom, use this article for information on early season strawberry disease control: Bloom is a Time for Strawberry Disease Management

Diseases: Once blossom buds are visible, some growers may choose to do a fungicide application for powdery mildew, leaf diseases, and anthracnose if these diseases have been problematic in the past. The most critical period for disease control starts at 5-10% bloom. 

Insects: Begin scouting for tarnished plant bug once the first blossoms start to open.

Refer to our new UMN Strawberry Farming Guide online for basic refreshers on planting, growing, and troubleshooting strawberries: Strawberry Farming - UMN Extension 

Tart Cherries

Lots of ants were hanging out on blossoms of a Romeo tart cherry bush. 5/18/22

Multiple tart cherry varieties are currently in full bloom. Northstar blooms unevenly, so some blossoms are at petal fall while other haven't bloomed yet.

If brown rot has been a problem in the past, this is an important time to spray a fungicide to combat this disease. There are few organic and many synthetic options available. See this article for more information!

Time sprays around rainfall events, with a protectant before a rain or a curative after a rain if the protective spray was missed. 

While infections are not currently visible right now, bloom and petal fall are times when the pathogen spores are infecting the blossoms in order to later cause rot on the fruit. Many fungicides are labeled for, and effective on, brown rot. Avoid use of FRAC 3 and 11 fungicides at this time to reduce fungicide resistance development, saving those for use later in the season when disease pressure is higher. Organic growers may use wettable sulfur.

Do not apply insecticides during bloom. Consider a plum curculio spray at or after petal fall, once bees are no longer foraging from the blossoms.

See the Midwest Fruit Pest Management Guide and this article for more information.


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