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Weekly Fruit Update - May 25, 2022


Honeygold apple tree at petal fall on a rainy day, 5/25/22

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

Weather was cool the past week, so we accumulated relatively few growing degree days above 50. Therefore, some of this content will sound eerily similar to last week. 


Bloom status was checked in Minnetrista, MN on Wednesday, May 25.

SweeTango is still in bloom, joined now by Honeycrisp and Macoun. At this particular site, Haralson, Zestar!, and Honeygold were all between late bloom to petal fall. 

Honeycrisp apple trees in full bloom on 5/25/22

Apple scab: Today's prolonged rainfall paired with an estimated 92% ascospore maturity mean that apple scab infection is extremely likely. More rain is possible in some places over the weekend. Growers should apply a protectant fungicide (i.e. mancozeb) prior to rainfall, or a kickback (curative) application of an effective systemic fungicide as soon as possible following the rainfall event. Applying the kickback within 3 days (72 hours) post-rainfall will control the existing infection. Generally speaking waiting longer than 3 days post-rainfall reduces the efficacy of the kickback application on the pathogen.

Plum curculio: Many orchards will reach petal fall this week. This is usually the time we spray for plum curculio. However, it is recommended to wait to spray for P.C. until 375 growing degree days (GDD) base 50 have accumulated. Today in Chaska, we are at 267 GDD. Therefore P.C. are unlikely to be out yet. Wait to spray until 375 GDD are reached, or until P.C. is observed at the orchard via scouting. How to scout for plum curculio.

Other: Next week we will be placing codling moth and apple maggot traps. Hail netting will be applied post-petal fall spray for our USDA-AGRI project evaluating hail netting for insect exclusion in high density apples.

Pesticides and pollinators: Evidence is clear that many insecticides, including organic insecticides, are fatal to bees if applied when they are foraging. In contrast, almost all fungicides are considered low risk or non-toxic 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.


Grapevine shoots currently range from 2 inch to 5 inches. This is the optimal time to shoot thin. Complete shoot thinning before the shoots are 11 inches - they can be removed easily by hand when they are small, and if we get warm temperatures over the weekend, shoots will grow rapidly. 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. 

Most grape pathogens spread and infect during rainfall events. Use protectants (i.e. mancozeb, Captan) before a rainfall, or curatives after rainfall if the protectant spray was missed. Use the Midwest Fruit Pest Management Guide to guide your spray decision; the guide contains tables comparing efficacy of each product on each disease.


Strawberries at many farms are currently in bloom. 

Diseases: Use this article for information on early season strawberry disease control: Bloom is a Time for Strawberry Disease Management. Diseases to target now include gray mold, anthracnose, and leaf spot diseases. Many products will also control powdery mildew. Anthracnose is not a problem in every years at every site; however, growers should spray for it if it has been problematic in the past.

The most critical period for disease control starts at 5-10% bloom. 

Tarnished plant bug: Tarnished plant bug is active during bloom and harvest, but does the most damage during bloom. It sucks liquid from blossoms, resulting in deformed fruit. Scout for tarnished plant bug now, twice per week from the very start of bloom until the end of harvest. Begin spraying if you see more than 1 bug per 4 plants.

Scout by placing a white paper sheet under a plant, and shaking the leaves to drop the bugs on the sheet. Repeat with a number of plants throughout the field. 

Read more on tarnished plant bug here.

This video shows how to scout for TBP: 

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 at petal fall.

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, 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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