As you walk the apple orchard this time of year, look for signs of key diseases on your trees. This helps predict what percentage of marketable yield to expect, evaluate how well your disease management program has worked, and implement any late season disease control measures if necessary. See the Midwest Fruit Pest Management Guide for summer cover spray recommendations. Here are some photos of key disease symptoms to look for this time of year:
Apple Scab lesions on fruit. These will vary in size as the disease progresses. Apple scab levels are low in 2020 due to dry weather the first half of June.
Apple scab (black/olive green) and Cedar apple rust (orange) on an apple leaf. Smaller scab lesions can be hard to spot. If having difficulty distinguishing scab and rust lesions, look on the underside of the leaf. CAR causes bumps, and scab causes subtle brown "fuzz" on the undersides.
The two photos above show different progressions of Cedar apple rust on fruit. The second photo shows the early onset of fruit infection, where the fruit may deform/discolor slightly in the infected area before developing bright orange lesions.
A mild infection of powdery mildew on an apple leaf.
Extreme pre-harvest fruit drop in a Minnesota apple orchard. Photo: Annie Klodd
Pre-harvest fruit drop is caused by ethylene production in the fruit. While it is natural and variety-dependent, it reduces yield and can be prevented. Factors that increase fruit drop include: Hot temperatures during the season, excessive crop load and clustering, summer pruning, insect damage, and disease. Practices that help reduce pre-harvest fruit drop include:
Frequent watering, to keep the soil at 50-70% field capacity
Good soil and foliar fertility - fruit low in Mg, or too high in K or B, are more likely to drop. Foliar testing as discussed earlier in the season is important for knowing the nutrient status of the trees.
Proper fruit thinning, to keep fruit an average of a fist-width apart
Maintaining a good pest management program throughout the season
Applying a stop-drop spray - NAA (FruiTone N, FruitFix 800, PoMaxa) should be applied 7-14 days before harvest, and before fruit drop is observed. ReGain reduces fruit drop by slowing ethylene production, but it also slows down ripening.
On Wednesday this week, we held the final vineyard webinar of the season in collaboration between UMN Extension and UW-Madison Extension. This webinar covered harvest-time insect pests, bird control options, and measuring fruit quality for harvest. Watch the webinar recording below, or on Youtube.
End of strawberry renovation window
A recently renovated strawberry field at Pine Tree Apple Orchard in White Bear Lake, MN. Photo: Annie Klodd.
Strawberry season ended for most growers in early July, while a handful of farms in more northern areas finished harvest last week. For the most part, fields should be renovated by this time. We published an article on strawberry renovation on July 2nd. If you have not yet renovated your strawberries, follow the steps outlined in the article. However, those renovating this late in the season may skip the mowing step. Furthermore, strawberries that were planted this year should not be mowed.
Author: Annie Klodd, Extension Educator - Fruit and Vegetable Production
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