Author: Annie Klodd, Extension Educator - Fruit and Vegetable Production, kloddann@umn.edu
Apples
Observations are based on weekly scouting in Minnetrista, plus multiple grower reports. Weekly scouting will begin in Preston and White Bear Lake next week.
Apple fruitlets at 6-7mm west of the Twin Cities on 6/8/2022. Photo: AK
Apples are between 5-10 cm diameter. Fruit set is variable, with some varieties and sites showing heavier fruit set than others. I have not noticed an overall trend at this time. However, we did have a long but cooler-than-optimal bloom period. If you have low fruit set paired with unpollinated flowers, that is a likely factor - bees are less active when temperatures are below 60 degrees F.
Management: Evaluate fruit set and crop load to determine whether or not to apply a chemical thinner. If you have already thinned once, walk the orchard to see how impactful it was, and whether another round is needed.
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| Codling moths in a Trece pheromone trap, 6/9/2022. Photo: AK |
Insects: Codling moth and plum curculio are active in much of Minnesota, but apple maggot is not yet. In Minnetrista, most traps contained over 20 codling moths. A spray application is recommended between 50-250 growing degree days (base 50) after traps detect the first flight of moths. Effective insecticides include Altacor, Assail, Delegate, Exirel, Rimon, and pyrethroids like Warrior, Danitol, and Mustang Maxx. Codling moth resistance to Imidan and Diazinon has been reported in several states. Fruit specialists widely recommend rotating among different insecticide modes of action and/or avoiding organophosphates like Imidan and Diazinon.
In addition to codling moth, plum curculio have also been active since petal fall. If you have not yet controlled them, include something with your codling moth spray that also has efficacy on plum curculio.
Apple maggot is not yet active (0 flies caught in Minnetrista on 6/8/2022).
If you have low/moderate crop load and don't need to thin, avoid use of carbaryl (Sevin) for these insect pests as it acts as a chemical thinner.
Disease: For those with early season varieties, it is soon time to switch from mancozeb to another protectant (i.e. Captan) to stay in compliance with the 77 day PHI of mancozeb. Diseases being targeted now include apple scab, fruit rots, cedar apple rust, and sooty blotch/fly speck. Apply a protectant prior to rainfall, to avoid the need for a more expensive kickback application after a heavy rainfall.
Grapes
Observations are based on weekly scouting in Minnetrista and Chanhassen, MN, and reports from growers around Minnesota.
Grape clusters in pre-bloom in Chanhassen, MN on 6/9/22. Photo: AK
Grapevines are in the pre-bloom period. Bloom may begin for many varieties in the next week in southern Minnesota.
Management: Grapevine shoots in southern Minnesota have surpassed the optimal period for shoot thinning. Growers can still thin if needed, but must use pruners to remove shoots now. Begin tucking shoots on VSP-trained vines as they exceed 18 inches long (tall enough to tuck into the bottom catch wire). Remove suckers and tie up loose cordons as needed.
Insects: Do not spray insecticides during grape bloom. Scout for phylloxera to determine the need to control it - control is not necessary every year. See last week's fruit update for information. We only occasionally see grape berry moth in Minnesota, and usually not in numbers that warrant an insecticide application. Growers see other insects like various caterpillars, worms, and flies at this time of year. Most of these insects are not economically significant and do not warrant an insecticide. Be sure to only spray for economically significant pests, and only if they are spotted in the vineyard in quantities above the economic thresholds, to avoid wasting money and harming beneficial insects. See the Midwest Fruit Pest Management Guide - Grape chapter.
Diseases: Fungicides may be applied pre-bloom or during bloom to prevent establishment of a variety of diseases including black rot, phomopsis, powdery mildew, downy mildew, and botrytis bunch rot. The time to control these diseases is the early season, even though symptoms do not show up until later. A number of fungicides are available, and they are listed in the Midwest Fruit Pest Management Guide. For protectants (sprayed before rainfall), it is time to transition away from mancozeb and toward Captan to avoid the 66-day pre-harvest interval of mancozeb.
Strawberries
Observations are based on site visits and photos from growers. I will begin weekly scouting in White Bear Lake next week.
Strawberries in bloom and fruit set in central Minnesota on 6/6/2022. Photo: AK
Strawberries are in full bloom. I have seen fields ranging from heavy flower set to moderate. We seem to have escaped any May freezes.
Management: Keep fields watered and weeded as we approach the harvest season. Do not apply nitrogen at this time unless the field was just planted this year or the plants are showing significant N deficiency.
Insects: If insecticides are needed for tarnished plant bug, time applications for the late evening or early morning when pollinators are not as active. Cyclamen mites are an occasional pest and do not usually require spraying; if damage is present in large quantities (1 in 10 leaves infested), a miticide may be warranted. However, the miticide will also kill beneficial mites and should be used sparingly.
Diseases: Rain is possible here and there over the next week. Growers can protect plants from anthracnose, botrytis, and leaf disease infections by spraying a protectant fungicide like Captan or CaptEvate before a rain. A kickback fungicide like Luna Sensation or Quadris Top can be sprayed to control several diseases after an infection event (i.e. rainfall) if the protectant is missed.
One instance of phytophthora crown rot in strawberry was identified this week. Phytophthora can be spotted at any time during the season, and right now is a good time to look for it before the harvest season. Look for poor stands with wilted, stunted plants and brown discoloration in the crowns. Phytophthora spores infect plants growing in wet or heavy soils during prolonged wet periods.
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| A strawberry field with plant dieback. One of the causes of plant dieback is phytophthora crown rot. Photo: AK |
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