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| Photo: Strawberry season has begun! |
Author: Annie Klodd, Extension Educator - Fruit Production. kloddann@umn.edu
In this week's update: Strawberry tarnished plant bug and thrips, codling moth on apples, grape post-bloom, raspberry cane borer, and blueberry dieback. Plus: Are Japanese beetles here yet?
Apples
Apple fruitlets are around 20-30mm in southern Minnesota and the metro area. Northern Minnesota areas like Duluth are about a week behind the metro based on my visit up north last week. The time for chemical thinning is rapidly coming to a close (or is over for some). If additional thinning is needed, hand thinning is the best way to go. However, many orchards have skipped chemical thinning or just doing a very light thinner this year because of slightly low or optimal crop loads.
Insects: Codling moth and tarnished plant bug are active. Keep checking codling moth traps at least weekly to determine if, what, and when to spray. The first biofix for codling moth happened about 2 weeks ago. After the first spray, entomologists recommend spraying again 10-14 days later if moths are present in traps. Examples of effective products include Altacor, Assail, Delegate, Exirel and Rimon. Read about the various products and the optimal timing for them in the Midwest Fruit Pest Management Guide, page 51 in the 2021-22 edition.
The first couple of Japanese beetles have been spotted in the metro and in southern MN this week; however, it will probably be a couple of weeks before significant populations emerge.
Diseases: Check the NEWA website to examine the likelihood of disease development in your area. According to NEWA models, 100% of apple scab ascospores have been released; this means that the primary infection period is over. If it was effectively controlled during the primary infection period, no further sprays are needed. Walk the orchard to scout for leaf and fruit infections. Risk of sooty blotch and fly speck is low, and no action is needed.
Strawberries
A number of farms are starting to harvest strawberries, and opening for U-Pick, this week. Happy harvest!
Insects: Tarnished plant bugs and thrips are both active now. Thrips are only an occasional pest in Minnesota, but when they are present they can be destructive. I did receive photos of thrips damage from one farm near the metro area yesterday, and saw likely thips damage near Farmington today. To scout for both of these insects, lay a piece of white paper under a flower cluster and lightly shake it to release the insects onto the paper.
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| Potential thrips damage on a strawberry, indicated by bronzing. Photo: Annie Klodd |
Diseases: Disease pressure is low during dry, hot periods like we are experiencing now. If rainfall does occur in the next 2-3 weeks during bloom and harvest, diseases to control for include botrytis and anthracnose, and leaf diseases. If spraying is necessary due to prolonged rainfall, choose products with very short pre-harvest intervals and re-entry intervals during harvest season. Refer to the Midwest Fruit Pest Management Guide for options.
Grapes
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| Phomopsis lesions on grapevine leaves are yellow with a black spot in the center. Photo: Annie Klodd. |
Grapes are in the post-bloom stage, with berries smaller than pea-size. Conditions were suitable for good pollination last week during bloom.; not too hot and not too cold.
Insects: My Extension colleague Marissa Schuh spotted a couple of Japanese beetles today in southern Minnesota. It will still probably be a week or two before we see significant amounts of them, but keep an eye out. Phylloxera galls should be easily visible now if they were not controlled earlier. Refer to this article for information on phylloxera management and biology.
Diseases: Disease pressure is low during dry, hot periods such as what we are experiencing now. Phomopsis and anthracnose lesions are visible now if an infection currently exists. The photo above is from a vineyard in southeast Minnesota last week.
Blueberries
Blueberry bloom has ended, and berries are forming.
A number of growers have reported, and I have witnessed, stem dieback throughout fields, on the upper part of the bushes. This is most likely from winter injury following a dry fall. Every winter blueberry plants are subjected to intense cold in Minnesota. Plants that are healthy going into the winter have a strong chance of survival, but those that have been stressed from drought or other issues are less likely to survive extreme cold.
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| A blueberry plant with stem dieback on the top half of the plant from winter injury. Photo: Annie Klodd |
Raspberries
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| Puncture marks made by female raspberry cane borers. Eggs are laid between the lines. Photo: Annie Klodd |
Floricane (summer bearing) raspberries are in bloom right now. If floricanes were leftover from primocane (fall bearing) raspberries, those are also in bloom or fruit set.
Diseases: Keep an eye out for cane diseases. If phytophthora crown rot is present, it may be evident now. Look for canes that have wilted and dig up the crown. If the crown has brown discoloration, it may be phytophthora. If not, it could be another disease like cane blight, spur blight, or anthracnose. Submit a sample to the UMN Plant Disease Clinic for diagnosis.
Insects: Raspberry cane borers are still actively laying eggs in primocanes. Smaller canes seem to be more susceptible in my own garden, but I do not know if this is a general trend. Remove affected cane tips below the serrated cuts made by the insect, and dispose of them to disrupt the insect's life cycle. Insecticides are thought to typically be unnecessary for this pest, and I was unable to find insecticide recommendations after consulting with entomologists. Find more information here.
Other crops:
Tart cherries - Fruitlets are still green and growing. Ripening for early varieties like Northstar may begin soon, but we still have a way to go in general. Look out for tarnished plant bug and plum curculio damage on fruit. Anticipate brown rot and spotted wing drosophila once fruit begin to ripen.
Honeyberries - May be anywhere between bloom and fruit ripening, depending on your location in the state and the variety.
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