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| Photo: Strong fruit set on Nova floricane-bearing raspberries in Chanhassen, MN. Photo: Annie Klodd |
Author: Annie Klodd, Extension Educator - Fruit and Vegetable Production. kloddann@umn.edu
In this week's fruit update: Strawberry harvest season, apple pest forecast, grape post-bloom tasks, raspberries and blueberries.
Updates Relevant Across Fruit Crops:
Most of Minnesota is in a "moderate drought" right now. This is impacting all fruit crops. For irrigation recommendations, read Irrigation Recommendations for Fruit Crops During Drought.
Dicamba and 2,4D
herbicide drift injury. The cutoff date for farmers to apply dicamba
was extended to June 30th in Minnesota this year. The hot, dry weather
and high winds make dicamba and 2,4D even more susceptible to
volatilization and drift, increasing the risk to neighboring specialty
crops. We all wish there were more that specialty crop growers could do
to protect their crops from drift. Some things you can do are to
communicate with neighbors about your sensitive crops, and to try your
best to know when herbicides are being applied around you in case injury
becomes apparent later on. If you do observe injury (which often does
not become visible for 2-3 weeks afterward) you can report injury to MDA
and/or submit samples to a private laboratory for testing. Visit this
page for a list of educational resources on dicamba and 2,4D drift, from Ohio State University.
Strawberries
Strawberries are in the first week of harvest in most locations. Growers are reporting good-sized crowds at U-pick farms despite the heat.
The ongoing drought and last week's record-breaking heat across Minnesota is causing fruit to be smaller than average during harvest. If temperatures remain over 90 degrees for extended periods of time, fruit tend to color up before reaching their full potential size. At least one farm is also reporting that their season is about to end one week after beginning, because the heat is causing so much stress on the plants.
In the last week, I also observed heat damage on day neutral strawberry plants growing on black plastic. Black plastic is a poor choice for this crop, especially in this heat, because it can easily overheat the growing zone of the plants and stunt their growth. Heat damage observed on plasticulture day neutral strawberries underscores the importance of following established recommendations to plant them on white-on-black plastic, with the white side facing up. If black plastic was used, and heat damage is occurring as a result, you may try applying straw to reduce the ground temperature.
Apples
At 500-600 GDD, codling moths are at peak egg hatch for the first generation. Apply effective insecticides for codling moth if 5 or more moths are caught in a trap within a week. This insect will remain active throughout the season.
Plum curculio pressure has been relatively light this year. It can still be active for the next couple of weeks.
Fungicide cover sprays at this time of the season target sooty blotch and fly speck. However, the need to apply fungicides for apples is minimal at this time, due to the lack of precipitation. Four hours of leaf wetness are required for diseases to infect, and the IPM Institute (AppleTalk conference call, 6/15/21) recommends spraying fungicide once 175 wetting hours have accumulated. I anticipate that this will be a very low disease year - at least there is one silver lining to the dry weather.
Grapes
Grapes are in full bloom to post-bloom depending on variety and location.
Growers should proceed with post-bloom fungicide applications if the clusters are past bloom. As described in last week's weekly update, I advise against applying fungicides during full bloom unless rainy weather necessitates it. Bloom-time fungicides have been shown to decrease yield by reducing fruit size (see last week's fruit update for more info). Since weather has been consistently dry, growers should definitely think twice before applying fungicides during bloom, and instead wait until post-bloom. Apply protectant fungicides like Captan prior to a rain event, and systemic fungicides after a rain event.
Post-bloom leaf removal (a.k.a. leaf pulling) may begin next week. A good time to do this task is when berries are pea-sized. "Leaf removal" means removing 2-4 leaves around the fruiting zone on each shoot in order to increase fruit quality, decrease cluster compactness, aid in ripening, and increase air flow through the canopy to prevent disease. This is a time-consuming task when done by hand. However, very few upper Midwest grape growers have invested in mechanical leaf pullers due to the high capital cost relative to revenue that grapes bring in. This article provides leaf removal recommendations: Considerations in the Timing and Application of Leaf Removal.
Raspberries
Summer-bearing raspberries are sizing up but are not yet at harvest. Continue monitoring for diseases like powdery mildew and cane blights, only treating if necessary. Be aware that spotted wing Drosophila will become active by the end of the month.
We just published a brand new 19-page guide to growing organic, high tunnel raspberries! All recommendations in the guide are suitable for organic production. Read more and download it here: New Guide to Growing High Tunnel Raspberries.
Blueberries
Blueberry harvest will begin in early July. Disease and insect pest management in blueberries is relatively low in Minnesota compared to larger blueberry-producing regions like the southeastern US and Michigan; little management needs to be done at this time unless diseases such as phomopsis or anthracnose have been issues in the past. Focus on weeding around plants, irrigating regularly (1-3 times per week), and preparing for harvest season.
A note on U-pick picking containers: From a food safety perspective, it is a good idea to use U-pick picking containers that can be cleaned between uses. Alternatively, give customers single-use picking containers that they take home. Reusing wooden picking containers that cannot be sanitized poses a food safety risk unless plastic liners are used.
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