Grand Rapids area tree fruit update - April 9, 2024

Apple scab season is here!

Weather update

Temperatures are continuing an upward trend with minimal frost concerns expected in the next week.

We are anticipating rain events starting late Wednesday, April 10, and continuing through Friday.

For a more detailed look at the upcoming weather forecast, Jeff Andresen, Michigan State University Extension agricultural meteorologist, has weekly 15-minute talks posted every Tuesday at our Fruit & Nuts Weather page.

Crop update

Apple buds are currently at 0.25-inch green and moving into 0.5-inch green this week. The Grand Rapids, Michigan, area will be moving quickly into tight cluster this week.

Maximum soil temperatures since April 1 have ranged from 57.4 – 43.1 degrees Fahrenheit at 2 inches soil depth at the Sparta Enviroweather station. At 4 inches soil depth, maximum soil temperature has ranged from 52.8 – 43.3 F. Roots start to become active and are able to take up water and nutrients starting at around 45 F and therefore are now active. Most fine roots that actively take up water and nutrients are located in the top 0.5 – 2 feet of soil depending on the rootstock. 

Growing degree day (GDD) accumulation since Jan. 1 as of April 9, 2024

Enviroweather station

GDD 42 F

GDD 50 F
















Kent City















We typically report GDD accumulation starting March 1, but this is not a typical year! We reached the required chilling hours on Jan. 15 to move into ecodormancy and start accumulating GDD. This means the heat we received in February mattered for this year’s crop. As such, I will be reporting GDD from Jan. 1 rather than March 1 this season.

Pest and disease update

Apple scab

The wetting period from April 1 – 5 was associated with a moderate risk of infection and 21 spores per rod. The brief rain event on Sunday, April 7, had no infection risk and only three spores per rod.

However, roughly 25% of ascospores are predicted to be mature at this time based on the GDD base 32 accumulation since March 1. With mature ascospores in the leaf litter, warm temperatures and rain predicted on Thursday and Friday this week, prepare for a high infection risk this week.

Fire blight

Copper applications for apple scab control can also help control emerging fire blight cankers to limit primary inoculum for blossom blight and fire blight. If you have had fire blight in the past two years, keep these cankers in mind.

Powdery mildew

As green tissue is starting to come out, so is powdery mildew. The mycelium overwinters in the buds, which can look feathered, shriveled and silvery white. The dormant fungus will then colonize this first flush of growth. These appears as flag shoots. Powdery mildew will also infect developing blossoms and can cause fruit to abort, distort or russet.

Treatment for powdery mildew should start around 0.5-inch green, which we are quickly coming up on. Keep in mind that while rain benefits other fungal diseases, powdery mildew benefits from dry weather. Be sure to maintain mildew control during dry weather periods too. Plants gain resistance with maturity but will be susceptible to powdery mildew until terminal shoot growth ends.

Early season insects

Keep an eye out for San Jose scale, woolly apple aphid and European red mite at this time of year.

Dormant oils can be a great tool for suffocating these early insects as they start becoming active and respirating. Keep temperatures in mind when planning these sprays (40 – 70 F) and keep a 48-hour buffer around frost events. This shouldn’t be too difficult this week. The general recommendation is 2 gallons of oil per 100 gallons of water per acre. Applications before green in sweet cherry and at green tip in apple are recommended. Later applications can be made until pink in apple, but the rate should be reduced to 1 gallon per acre to avoid any tissue damage.

Insects coming soon

Green fruit worm and red banded leaf roller were caught in southwest Michigan this week. They will likely make an appearance in our area soon.

For more information about regional reports, please visit the Michigan State University Extension website.

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