Weekly Fruit Update - 8/14/2020

 In this week's update:

• COVID-19 guidelines for apple orchards and pumpkin patches - PLEASE READ
• What to do after blueberry harvest
• Prepping strawberry beds for winter

COVID-19 guidelines for apple orchards and pumpkin patches - PLEASE READ

In light of COVID-19, the state of Minnesota developed sets of guidelines that pertain to different types of businesses/entities such as recreational, entertainment, retail, restaurants, etc. While farms that operate solely to sell produce and/or offer U-pick are only subject to the guidance for Food and Agriculture, farms also offering agrotourism activities such as corn mazes, jumping pillows, and petting zoos become subject to recreational or entertainment guidelines. These guidelines include a 250 customer maximum at any given time. 

Our team is currently drafting an article to communicate details on this, based on a meeting yesterday with the Commissioner of Agriculture, Dept. of Labor and Industry, MN Dept. of Health, and MN Dept. of Agriculture to get clarification on these rules. We will release this article as soon as possible. In the meantime, please read this article to decide which set of guidelines your farm should follow, and to find links to the written guidance.

Note: The role of UMN Extension's horticulture team in regards to COVID-19 is to help growers access the information they need; Extension is not involved in the development of regulations in any way. For further information on the state guidance, contact the Minnesota Department of Labor and Industry.

Pumpkin cannons are an example of an agrotourism activity that would put a farm in the "Entertainment and recreation" category according to the state's COVID-19 guidelines. Photo: Annie Klodd.

What to do after blueberry harvest

The blueberry harvest is wrapping up across Minnesota. What to do next? Fall is a good time to replenish soil nutrients and tweak the soil pH if needed. Here is a quick to-do list:

• Foliar nutrient test in early-mid August
• Soil test (if not done in last 3 years, or to diagnose a problem)
• Amend soil pH if needed
• Apply soil fertilizer if needed - but no nitrogen
• Perennial weed management

A blueberry field during harvest season. Photo: Annie Klodd.

Late July to mid-August is the best time to collect leaves for a foliar nutrient test for blueberries. While soil testing shows the nutrient concentration of the soil, foliar testing shows how much of each nutrient is actually being taken up by the plant. This is very important in blueberries, as they are sensitive to the soil pH - pH levels strongly impact soil nutrient uptake by the plants, and pH above 5.6 reduces uptake of certain nutrients. Foliar tests catch nutrient deficiencies so they can be corrected. See this video for information on foliar sampling, and submit samples using the "Diagnostic Plant" form at soiltest.cfans.umn.edu. 

Correcting nutrient deficiencies in blueberries may require amending the soil pH, in addition to applying fertilizer. Soil testing will reveal the soil's pH, allowing you to then apply the appropriate amount of sulfur to lower the pH to ideal levels for blueberries. The idea pH range for blueberries is 4.5-5.5. Fall is a fine time to submit a soil test, but this can also be done at any point in the growing season.

When amending the soil based on the foliar and soil tests, most macro- and micronutrients can be applied in the fall, except for nitrogen. Do not apply nitrogen to blueberries after the beginning of harvest in Minnesota. Late season nitrogen application can increase winter injury, because it encourages the plants to put on excess new growth too late in the year, inhibiting their ability to harden off for the winter. 

Fall is also a great time to manage perennial weeds. While there are multiple cultural and mechanical methods for perennial weeds that can be done throughout the season, this comment mainly pertains to herbicide application. Herbicides applied to perennial weeds in the fall can be trans-located into the plants' roots as they harden for the winter, leading to more effective die-back of the weeds. Common perennial weeds in Minnesota blueberry plantings include Canada thistle, creeping Charlie, and quackgrass. Herbicide options can be found in the Midwest Fruit Pest Management Guide.

Prepping strawberry beds for winter

A strawberry field several weeks after renovation. Photo: Annie Klodd.

Between renovation and dormant straw application in November-December, the plants must be kept healthy to support the production of next year's flower buds. Flower buds for the following year's harvest are produced in the current year, following the final harvest. Here is a to-do list for post-renovation in strawberries:

• August N fertilizer
• Foliar and soil testing
• Runners
• Irrigate until late September
• Straw
• Weed control 

We are at the window for final nitrogen application in strawberries. A late summer application of approximately 30 lb/acre of N is recommended between early August to early September. In sandier soils, consider applying this in two split applications to reduce losses to runoff during rain events. Keep in mind that nitrogen should not be applied to strawberries in the spring unless the plants are exhibiting deficiency. Therefore, this will be the final N application window until the next season's renovation. Applying it now will encourage runner formation for the next few weeks until the plants harden off for winter.

Foliar testing should also be done at this time for strawberry plants, in order to identify and correct nutrient deficiencies. The small testing fee may save hundreds of dollars of unneeded fertilizer or greatly increase yield by alerting you of a yield-limiting deficiency. See this video for information on foliar sampling, and submit samples using the "Diagnostic Plant" form at soiltest.cfans.umn.edu. 

Eliminate runners between the rows, to encourage the plants to focus energy on daughter plant production in the rows. Runners between rows can be eliminated by tillage, or light cultivation can be used to brush them into the rows.

To promote runner formation and daughter plants in the rows, irrigation weekly throughout the fall in order to maintain one inch per week of water. Maintain good weed control to minimize competition for water, nutrients, and space.

Straw should be applied once the plants are dormant and temperatures drop to the low 20's. Another rule of thumb is to apply straw once temperatures consistently drop to 40 F for three nights in a row. Depending on location, this typically occurs sometime in mid-late November in Minnesota. In order to get a straw layer 2-4 inches deep after settling, apply 2.5-3 tons/acre of wheat, oat or rye straw, or 5-6 tons/acre of shredded corn stalks. Be aware of what herbicides were applied to the straw prior to cutting; strawberries can be injured by herbicide residues of aminopyralid (i.e. Milestone, Stinger) and picloram (i.e. Grazon) contained in the straw (more info).

Weeds should be managed throughout the fall in order to reduce competition and support daughter plant growth. In addition to cultivation, hand weeding and flame weeding, certain herbicides can be applied between the rows and over the rows in the fall. Options for fall over-the-row application include:

• Dacthal – Preemergent. Grasses, some broadleaves
• Devrinol – Preemergent. Late fall. Grasses, some broadleaves. 
• Sinbar 80WP – Preemergent. Late fall. Grass & broadleaves. Some varieties sensitive!
• Poast – Postemergent. Grasses. Caution w/ Poast+Sinbar.
• Ultra Blazer 2E – Postemergent. Grass & broadleaves. Late fall once dormant. Effective on marestail (a winter annual coming up in fall)
• For more options and information, see the Midwest Fruit Pest Management Guide.

Author: Annie Klodd, UMN Extension Educator - Fruit Production. kloddann@umn.edu.