Grand Rapids area tree fruit update – April 2, 2024

The region is cooling off after a hot start to the growing season.

Weather update

We are expecting cloudy, cool, windy and wet weather Tuesday, April 2, through Thursday, April 4. The Grand Rapids, Michigan, area is anticipating mixed rain and snow with minimal snow accumulation. Friday through Sunday should be fair and dry. With more rain anticipated next Monday, this weekend will be an optimal time for apple scab sprays. The medium range forecast calls for a return of above normal mean temperatures and near to above normal precipitation totals. This predicted warmer and wetter weather can push primary apple scab season along, so be sure to stay on top of management decisions.

Additionally, while there is a chance of snow this Wednesday/Thursday, we are not anticipating any temperatures lower than 27 degrees. This temperature is not of concern for half-inch green tip but may be of concern if apples are at tight cluster (see Critical Temperatures for Frost Damage on Fruit Tree from Utah State University Extension for more information). If you have early varieties at tight cluster like Idared or Zestar!, consider using frost fans during upcoming cool nights if the temperature inversion potential is adequate.

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

Apples in the Grand Rapids area are currently primarily at green tip and moving into 0.25-inch green. This phenology is in line with the growing degree days (GDDs). We predict green tip at 127 GDD42 and 51 GDD50 and 0.25-inch green at 189 GDD42 and 82 GDD50 for McIntosh. The GDD accumulations are between those two benchmarks in most areas. This recent cool weather has slowed down phenological development significantly.

Growing degree day (GDD) accumulation since Jan. 1

Enviroweather stations


















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

Woolly apple aphid

We have found live woolly apple aphids overwintering in the canopy across the Grand Rapids area. Typically, this population will overwinter in the root system and crawl back up to the canopy in the spring. Any remaining canopy populations will die in normal Michigan winters. This was not a normal winter.

Dormant oils are a great option for controlling woolly apple aphids and other early season insects like San Jose scale or European red mite at this point. Dormant oils should be applied when temperatures are between 40-70 degrees Fahrenheit and with a 48 hour buffer around frost events. They should also not be mixed with sulphur or Captan due to phytotoxicity concerns. Dormant oils can be applied until the pink stage. Despite being called dormant oils, they are more effective later in the season when insects are more active. Dormant oils are most effective when insects are actively respirating on warmer days.

Apple scab

I caught eight Venturia inaequalis ascospores/rod following the rain event on Saturday, March 30 – Sunday, March 31.

We have warmer and wet weather predicted in the next couple of weeks which is optimal for ascospore development and release. Please ensure that cover sprays are on when possible!

If using copper, consider more fixed coppers that are less water soluble than copper sulfate formulations. With multiple rain events predicted, this will help ensure coverage throughout the week.

Fire blight

Overwintering fire blight cankers are starting to wake up as we enter spring. If you have had fire blight issues in the past two years, copper sprays can limit the inoculum pressure before bloom and shoot blight starts.

Powdery mildew

Powdery mildew will kick off as soon as green tissue is available. Be on the lookout for silvery flag shoots as buds open and consider incorporating a powdery mildew spray. Initial control early in the season is important to prevent the polycyclic disease cycle from continuing and causing bigger problems later in the season.

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

Did you find this article useful?