Fruit update - 05/08/24

UNIVERSITY OF MINNESOTA EXTENSION - www.extension.umn.edu

Many parts of Minnesota are still experiencing a rainy spring, which can impact disease incidence from longer durations of leaf wetness, as well as decreasing the overall opportunity for growers to get out and apply fungicides.

For folks who are monitoring insect pest development, about 182 growing degree day units have accumulated (baseline 50F) in the twin cities area as of 05/08/2024. Upcoming weather forecasts and the frost date calculator indicate that many regions in Minnesota can plan to be finished with spring frost incidences for this growing season.

This fruit update contains information about…

Apples - growth stages, tree management, and diseases.

Grapes - growth stages, vine management, and diseases.

Strawberries - growth stages and diseases.

Honeyberries - bloom update.

Apples

Image: SweeTango at two different growth stages, locations, and growing seasons. Notice the accelerated growth from this year as compared to 2022, which could be due to a milder winter season, or local climate impacts, among other factors. Photo on left taken by Annie Klodd.

Growth stage: Many apple orchards are experiencing bloom in the lower half of Minnesota. Although growth stages for any given year are dependent on multiple factors, many places do appear to be ahead for the 2024 growing season.
This week at the UMN Horticulture Research Center, UMN researchers and partners are doing pollination crosses for the apple breeding program.

Image: An apple tree trained on a high density, trellised system showing signs of trunk girdling from a tight T-band that was originally used to maintain tree placement during establishment.

Tree management: Apples require a method to secure trunks onto training stakes or wires during establishment. Rubber T-bands are one way to do this; however, they do need to be adjusted overtime and eventually replaced or removed to prevent trunk girdling, which can wound trees and lead to leaking sap and subsequent opportunistic fungal colonization. 

Diseases: The NEWA Apple Scab tool projected a high likelihood for infection on 05/07/2024 in the twin cities area, based on the weather station at the UMN Horticultural Research Center (Chaska, MN, Zone 5a,) due to the combination of rain, a long leaf wetness period, and warmer temperatures. 

Growers who are experiencing similar weather conditions and are concerned about missed preventative fungicide applications or experienced very little time between fungicide applications and a rain event are not guaranteed an infection. Successful infection require the pathogen's presence in addition to a favorable environment. However, if a preventative fungicide application was somehow missed, applying a properly-timed fungicide with curative action can still be an option for growers who are concerned about an infection event. Refer to the Midwest Fruit Pest Management Guide to determine which fungicides are most appropriate for your situation.

Grapes

Images: Grape buds pushing toward budburst and emerging from one-year-old canes. Photo (left) taken at the University of Minnesota Horticulture Research Center near Chaska, Minnesota (Zone 5a; photo taken by Drew Horton) and in SE Minnesota (right), near Rochester. Minnesota (Zone 4b).

Cold climate grapes have continued to develop this past week and many have reached budburst with visible leaf tips. Canopy management: Growers can continue tying new cordons to the fruiting wire and should keep an eye on shoots with a plan to thin excess shoots and secondary shoots before they reach 11 inches tall. After grape shoots pass 11" tall, they tend to be a lot less tender and become more challenging to remove by hand. Similar to many vineyard canopy tasks, well calculated timing makes for easier thinning. Grape growers can also check ag-lock, T-bands, or other supplies used to band trunks to training stakes and cordons to the fruiting wire. If banding supplies are becoming too tight, replace them with larger sizes to prevent girdling. Diseases: Routine spraying for various fungal pathogens like phomopsis cane and leaf spot, anthracnose, and black rot will become critical starting at the time when grapes are between 1-3” tall. To learn more about grape diseases and appropriate fungicides to apply, refer to the Midwest Fruit Pest Management guide.

June-bearing strawberries

Images: An early blooming June-bearing strawberry variety known as ‘Annapolis’ (left) and a late blooming variety ‘Flavorfest’ (right). Strawberry photos taken at Firefly Berries in Rochester, Minnesota (Zone 4b).

Growth stage: Growers in most areas of Minnesota who produce June-bearing strawberries have already uncovered their strawberries. Earlier varieties, such as ‘Annapolis’ (pictured above) have begun to bloom in SE Minnesota, while later varieties like ‘Flavorfest’ are still vegetative.

Image: A June-bearing strawberry leaf showing symptoms of a leaf spot disease sighted in SE Minnesota.

Diseases: Some growers may anticipate observing a higher incidence of leaf spot diseases this year on June-bearing strawberries. One type of leaf spot disease, known as Common leaf spot of strawberry (Mycosphaerella fragariae) is spread by water from rain or overhead sprinklers making contact with spores on the ground and splashing them onto the plants. If a grower knows they are dealing with Common leaf spot, the issue can be cosmetic, especially if it is not widespread.

However, because leaf spots diseases cannot be diagnosed by pictures alone, it is best to test and confirm the causal agent with a plant disease clinic. Other strawberry leaf spot diseases include Angular leaf spot, Septoria leaf spot, leaf blight, and leaf scorch. To learn more about strawberry disease management, visit the UMN Extension webpage, "Strawberry diseases in Minnesota."

Honeyberries

Image: Honeyberries are finishing blooming in SE Minnesota. Reports from NE Minnesota share that honeyberries are still in full bloom.

Honeyberries are finishing blooming in SE Minnesota and are currently blooming in the Duluth area.

The University of Minnesota Extension fruit production program would like to extend a thank-you to the growers who make these reports possible.