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Weekly Fruit Update - May 19, 2021


As the dandelions blow away their seeds, the bees are grateful for the abundance of blossoms on our apples, stone fruits, and blueberries. Read on for timely recommendations on these crops as well as grapes, raspberries, strawberries, currants, and kiwiberries.

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

Apples: Apples are between full bloom and post-bloom, depending on the variety. For example, at the UMN HRC  SweeTango was about 75% full bloom and 25% post-bloom while Honeygold was at post-bloom as of 5/18/21. Infection periods for fire blight and apple scab have been minimal due to dry weather. 

Petal fall sprays should target apple scab, Cedar apple rust, powdery mildew, as well as bitter rot and fireblight if needed. The peak hatch of red-banded leafrollers coincides with petal fall, so they should be controlled now to prevent late season problems. Scout for plum curculio, and control it at or shortly after petal fall. Other insect pests of note at this time include aphids, mites, spotted teniform leafminer, and white apple leafhopper. Pyrethroids are not recommended at petal fall, because they kill predatory beneficial mites that prey on pests like European red mite and twospotted spider mite. Refer to the Midwest Fruit Pest Management Guide for spray recommendations. 

Some growers begin chemical thinning during petal fall. This strategy allows the grower to evaluate the impact of the first thinning before deciding whether to thin again during fruit set. Sevin, Amid-Thin, Maxcel, and NAA can all be used during petal fall. This article from Dr. Amaya Atucha at UW-Madison Extension lists thinner options and gives example scenarios.

Minnieska (SweeTango) blossoms at bloom and post-bloom, UMN HRC, 5/18/21.

Grapes: At the UMN HRC, grapevines are well past bud break and are between 2-5 inch shoots in most cases. In Scandia, MN (north of Stillwater) shoots are 1-3 inches. We expect shoots to grow rapidly in the next week, especially with the warm temperatures and expected rainfall. Growers should prepare to initiate shoot thinning over the weekend or by Monday, so that thinning is complete before shoots reach 11 inches. Insect pest concerns are minimal at this point, making insecticide applications largely unnecessary unless foliar phylloxera is a significant concern for the vineyard. Apply your bloom fungicide application, and time the next application based on rainfall; the spray interval may be extended if dry weather continues, as dry conditions are less conducive for disease development.

Marquette grapevine shoots between 2-4 inches long, in Excelsior, MN, 5/18/21

Itasca grapevine shoots between 3-5 inches long, in Excelsior, MN, 5/18/21


Strawberries: In southern MN, day neutral strawberries should be planted by this point, or very soon. Continue removing flowers from day neutral strawberries for about 3-4 weeks after planting. Warming soil temperatures are strengthening growth of June-bearing strawberries across the state. Due to the extended dry weather across the state, monitor soil moisture and irrigate as needed. 

As bloom approaches, scout for tarnished plant bug and spray to control them if necessary. Feeding that occurs on the blossoms during bloom causes damage to the fruit, so this is the time to keep an eye on them. Additionally, look for two-spotted spider mites and cyclamen mites. This article on tarnished plant bug also links to articles on various spring strawberry insect pests. Disease control is extremely important during early bloom to bloom, so prepare a plan ahead of time for your bloom sprays. Refer to the Midwest Fruit Pest Management Guide for specific disease recommendations.

Crews irrigate a strawberry field at Pine Tree Orchard in White Bear Lake, 5/14/21

Raspberries: Summer-bearing (floricane) raspberries are beginning to exhibit the first closed blossoms of the season. They are not quite at pre-bloom, so it is still too early to do pre-bloom pest management. Fall-bearing (primocane) raspberries should be between about 6-18 inches tall at this point, depending on production system, irrigation practices, and location in the state. There is very little to be done in raspberries right now, other than weed control and consistent irrigation to help new primocanes develop.

High tunnel primocane raspberries were about a foot tall on 5/14/21, at Little Hill Berry Farm in Northfield.

Blueberries: Blueberry varieties are in various stages of bloom, depending on variety and location across Minnesota. Diseases to control during bloom include mummy berry, phomopsis, and botrytis fruit rot. Not all of these diseases may be a problem at all Minnesota farms, nor do they become problematic every year. For many MN farms, botrytis may be the most significant blueberry disease concern. While it is important to be proactive with disease control to minimize the risk of fruit losses, growers in our climate should also consider the history of disease occurrence on their farm as well as the weather to determine which diseases to focus on at this time.

Stone fruit: At the UMN HRC, tart cherries are between full bloom and post-bloom, depending on the variety. Fruit set has begun in North Star, pictured below. North Star is an earlier-ripening cherry that sometimes ripens in late June before SWD is highly active. Meteor is still in full bloom. Plums including Mount Royal, Toka and Alderman are also in late bloom and petal fall. 

Do not spray insecticides on stone fruit during bloom. A petal fall brown rot fungicide application should be made if brown rot has been a problem in the past. Additionally, scout for plum curculio at this time, and apply appropriate insecticides at or after petal fall if necessary. See the Midwest Fruit Pest Management Guide for spray program recommendations at each phenological stage.

Petal fall and the beginning of fruit set in North Star tart cherry, Excelsior, MN 5/18/21

Petal fall in Toka plum, Excelsior, MN, 5/18/21

Currants: Red currants are at fruit set and are on target to be harvested as normal in mid-June. 

Strong fruit set on a red currant bush in Chanhassen, MN, 5/18/21

Kiwiberries: Kiwiberries have not bloomed yet, but unopened male flower clusters can be seen on A. arguta at the UMN HRC in Excelsior. Seth Wannemuehler, UMN graduate researcher studying kiwiberries, predicts that they will likely flower early next week.

Unopened flower cluster on male A. arguta kiwiberry vine, Excelsior, MN, 5/18/21

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