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Weekly Fruit Update - June 9, 2021

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

This week's fruit update includes: Apples, grapes, raspberries, and strawberries. Key issues addressed include drought and heat, Japanese beetles, and foliar testing.


1) Crop Reports:


Apples have sized up nicely with the warm weather. Many varieties are between 15-25 mm. 

Apple fruitlets around 20 mm, June 9th.

The cutoff for chemical thinning is 25 mm, and only certain combinations of thinners will work between 15-25 mm. NAA becomes ineffective after 20 mm. One recommended tank mix for rescue (late) thinning is Ethrel + Sevin + horticultural oil. Be cautious with this application for several reasons: 1) Horticultural oil can cause phytoxicity if used within 2 weeks of sulfur application, and 2) under-thinning and over-thinning can both occur depending on weather conditions and current fruit load. We are unable to say exactly how many fruit will thin off with this application, because too many variables are at play. Carefully consider whether this application is worth the risk before implementing it. Wait a week after the last application to make a decision, to observe its effects.

Codling moth, red-banded leaf roller, and plum curculio are active. Japanese beetle adults are not yet active.


Grapes are at full bloom across the state this week, across many of the main varieties. 

Itasca flower cluster in full bloom, Scandia, MN, 6/8/2021. Photo: Jake Powell

Important memo on fungicide application (including organic fungicides!): My current recommendations is to not apply fungicides during grape bloom unless absolutely necessary, especially copper. 

Research from Michigan State University found that fungicide application during bloom can reduce yield. The amount of damage depends on the fungicide, with copper, Ziram, and oxidate having the most damaging effects. Read more here: Fungicides applied at bloom may reduce fruit set in grapes.

Due to the extended hot, dry conditions, grape growers should be able to leave longer intervals between fungicide sprays, and it should not be necessary to spray during bloom unless extended rainfall occurs.


Floricane-bearing raspberries are currently in bloom. Keep your eyes out for our new guide High Tunnel Organic Raspberry Production, which we will release very soon! 


It is not possible to say exactly when June-bearing strawberry harvest will begin, but it will be soon - very likely some time next week. Strawberries are beginning to color due to the high heat. One potential issue, which I have heard about from a Michigan State University Extension Educator but has not been reported to me yet from any Minnesota growers, is small fruit size. The extended heat may cause some berries to start coloring up before reaching their full size potential, so keep an eye out for this.


2) Current events:

Prepare for Japanese beetles

Japanese beetles aggregate and feed on leaves, creating a distinctive "skeletonized" look on the leaves. Photo: Annie Klodd

Japanese beetle (JB) emergence will start in the 3rd or 4th week of June, and adults will continue feeding on leaves through September. Now is the time to prepare a plan for managing them - what cultural management practices can you implement to reduce populations? What will you spray, and how will you know when it is time to spray? This article discusses all of that and includes a video with more detailed information: Preparing for the Emergence of Japanese Beetles in Fruit Crops.

Watering during this dry spell

A key question right now is when to water long-lived perennial crops like apples and grapes during extended dry periods. 

Most grape growers in Minnesota do not use irrigation systems because they are so rarely needed for this crop in our climate. While many apple orchards in Minnesota do have irrigation systems, others do not. When the only option is hand-watering with a tank, it is not obvious when conditions have gotten bad enough to start watering. 

Right now, Minnesota is far behind normal precipitation levels for this time of the year. Furthermore, fruit crops are all at sensitive growth stages that require a lot of water. Grapes are at bloom, strawberries are rapidly developing fruit, and apples are forming next year's flower buds (return bloom). Lack of water during return bloom can lead to poor fruit set the following year. Maintaining soil moisture is particularly important for recently planted grapes and apple trees, as their root systems are too small to forage deep for water. Even if using manual watering from a tank, try to maintain 1 inch of water per week.

Foliar nutrient testing

Collect foliar tissue samples into a paper bag, such as those provided by the UMN Soil Testing Laboratory. Photo: Gail Hudson.

While soil testing tells the concentration of each relevant nutrient in the soil, foliar testing is an important way to tell how well the crop is actually taking up those nutrients from the soil. For this reason, we recommend fruit growers do foliar testing every year and soil testing only once every 3-5 years. The timing for foliar testing depends on the crop:

  • Grapes: During bloom (right now) or veraison
  • Apples: Mid-July to mid-August
  • Blueberries: First week of harvest
  • Strawberries: Mid-August
  • Raspberries: First week of August

Therefore, the only major fruit crop to sample right now is grape. However, if a nutrient deficiency is suspected for any crop, it can be sampled now for diagnostic purposes. Read this new webpage for information on how to sample and submit samples for testing: Foliar Testing for Fruit and Vegetable Crops.

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