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Weekly Fruit Update - 8/6/2020

In this week's update:

  • Berry webinar next week
  • Post-season blueberry to-do list
  • SWD and Japanese beetle updates
  • Comparing bird management tactics
  • COVID and fall apple & pumpkin season
  • Applying pesticides during rainy periods 

Berry Grower Webinar Wednesday, Aug. 12

We will be holding a berry grower webinar next Wednesday, Aug. 12 at 1:00pm. This 1-hour webinar will cover spotted wing Drosophila research, Japanese beetle management, and preparing strawberry and blueberry crops for winter. This webinar is co-hosted by UMN Extension and UW-Madison Extension. Please see this link to register.

Post-season blueberry to-do list

A young blueberry bush exhibiting nitrogen deficiency. Photo: Annie Klodd.

Soil tests: Late summer is a great time to take soil samples to submit for soil nutrient testing in berry crops. Taking the samples now allows sufficient time to get the results back and amend the soil in the fall. Information on taking soil samples can be found in this video. Submit soil samples to the UMN Soil Testing Lab: soiltest.cfans.umn.edu. 

Foliar nutrient tests: The best time to take blueberry foliar samples for nutrient testing is late July to early August. To sample, take 5 leaves each from at least 10 plants (50 total) throughout the area of interest. If one section of the field is experiencing problems, do a separate sample for that area in order to compare it to healthier parts of the field. Foliar testing is critical in blueberry production. It measures how well nutrients are being acquired by the plants, and it presents an opportunity to optimize your fertilizer program. Yield and vigor can improve through more precise fertilization, even if the deficiencies are not visually apparent.

Sulfur pH amendment if needed: Additionally, fall is a time to amend the soil pH for blueberries, if the soil test indicates that it is too high or low. The ideal pH range for blueberries is 4.5-5.0. While they can tolerate a pH slightly high or low, a pH of 5.6 will decrease plant vigor and cause nutrient deficiencies. Elemental sulfur is a common pH amendment for acidifying the soil. Sulfur takes weeks or months to alter the soil pH, so applying it this season will help the plants overwinter and grow better in the spring. Sulfur sources include elemental sulfur, ammonium sulfate, and aluminum sulfate. Do not use aluminum sulfate, as it is expensive and may injure the plants. Do not apply ammonium sulfate in the fall, because the addition of ammonium (nitrogen) in the fall can decrease the crop's winter hardiness and cause winter injury. Elemental sulfur is the most economical option. On a sandy loam soil, it takes 600 lb/acre of elemental sulfur to reduce the pH by one unit (from 6.0 to 5.0). Applying this in 2-3 split applications is best if a large amount is needed.

Add phosphorus and potassium if needed - but no nitrogen: Depending on the results of the soil and foliar nutrient tests, fertilizer may be needed. Phosphorus and potassium can be applied to the soil as a granulated fertilizer, or through fertigation. They may be applied in the fall. However, it is important not to apply nitrogen fertilizer after harvest. Nitrogen additions after early July cause flushes of leaf and shoot growth too late in the season, so that the plants do not harden off properly for the winter. This leads to subsequent winter damage. 


Foliar fertilization for blueberries has not been shown to have consistent benefits in peer-reviewed research studies. 

SWD and Japanese Beetle Updates

SWD and Japanese beetles continue to cause challenges for berry growers in parts of Minnesota. Please see this article for an update on population counts, and important information about organic and conventional insecticide use for Japanese beetles.

Comparing Bird Management Tactics

Netting covering rows of apple trees at Pine Tree Apple Orchard. Photo: Annie Klodd

Spoiler alert: Netting is still the most reliable method for keeping birds off of berry crops. Why? Well, because it is not-discriminatory. It excludes all birds equally, regardless species because it is a simple, physical barrier. Other methods such as recorded distress calls, spray repellents (methyl anthranilate) cannons, gun shots, drones, and lasers are more effective on some species than others. That is because different birds react differently to these stimuli. To hear a review of these methods, and what the research says, watch our webinar from last week, starting at 19 min, 55 sec: 


COVID and Fall Pumpkin and Apple Season

We are a few weeks away from the start of apple season in Minnesota. Photo: AK

Understandably, growers have many questions about how the state regulations around COVID-19 apply to the fall season for apple orchards and pumpkin patches. We will be meeting with representatives from MDA, MDH, and DLI next week to get clarity on the regulations. From there, we plan to write a fact sheet outlining what we learn, and share it with you. In the meantime, growers are welcome to call the Minnesota Commissioner of Agriculture office with questions, and they will help direct you to the appropriate person to answer the questions. Additionally, refer to the resources below:

Resources available: 

Applying Pesticides During Rainy Periods

While the weather has been relatively dry the last couple of weeks, rainy days are in our future. Rain complicates the timing of pesticide application, whether applying conventional or organic products. Some products are more sensitive to runoff by rain than others. This short article from Michigan State University gives some helpful information about how rain impacts spraying.

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

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