Grand Rapids area tree fruit update - April 30, 2024

Apples are moving into full bloom.

A bee visiting an apple blossom.
Photo by Lindsay Brown, MSU Extension.

Weather update 

The Grand Rapids, Michigan, area had minimal damage associated with the hail event last week. The frost did not cause damage across the region. However, some areas in low spots or more north towards Kent City, Michigan, did see some damage.  

We will have continued warming this week with rain showers on Friday, May 3.  

For a detailed look at the upcoming weather forecast, Jeff Andresen, Michigan State University agricultural meteorologist, has weekly 15-minute weather forecasts posted every Tuesday. 

Crop update 

Early season apple varieties are in full bloom (Ida Red, Zestar!, Liberty, Pink Lady, etc.). Other apples varieties are at king bloom and will move into full bloom this week.  

Bud development advanced rapidly from last week. With warmer temperatures, there has been a lot of pollinator activity over the past few days. Commercial honey bee and bumble bee hives will arrive in orchards over the next few weeks for pollination of cherry and apple. Honey bees will forage at temperatures of 65 degrees Fahrenheit or warmer. Bumble bees and solitary bees will forage at temperatures 5-10 degrees cooler than honey bees. As we approach bloom, implement practices that minimize pesticide exposure to bees by using reduced risk pesticides and spraying at times when pollinators are not active. Find tips and guidelines to minimize bee pesticide exposure.  


Pest and disease update 

Apple scab 

Last week, we had two rain events associated with ascospore release. Following the rain event from 7 – 10 p.m. on April 23, I saw an average of 2,324 ascospores per rod. Following the rain event from 9 p.m. April 26 – 8 a.m. April 27, I saw an average of 486 ascospores per rod. During the rain event from 8 a.m. – 1 p.m. on April 28, I sampled at 11 a.m. and saw an average of 1,384 ascospores per rod. This rain event had high potential for scab infection between the continued rain, the warm weather and the built up ascospores ready to infect.  

The Rimpro model is indicating that April 27 – 29 is an extreme infection risk period for apple scab in the region.  

This week will have some continued small rain events.  

Fire blight 

As the Grand Rapids area moves into bloom over the next week, start thinking about blossom blight. April 27, 28 and 29 are high risk periods with an epiphytic infection potential (EIP) of 40, 65 and 70, respectively. April 30 – May 03 are medium risk days with EIPs of 77, 74, 98 and 98, respectively. Double check the Enviroweather fire blight website throughout the week to stay on top of any changes. With these higher EIPs, treat blossoms as they open up with a stronger bactericide like strep or kasumin to make sure bacterial populations stay under control. 

These warm temperatures during bloom are perfect for bacterial population growth.  

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 be currently ongoing. 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.  


Green fruitworm and spotted tentiform leafminer were detected in the Grand Rapids area this week.  

Obliquebanded leafroller and oriental fruit moth have also been spotted in the area.  

Woolly apple aphids are becoming more active and developing their characteristic hairy look again. Treating these with a systemic like Movento or Senstar at petal fall is critical for their control. Senstar has Esteem in it too, which is highly effective on San Jose scale.  

Keep redbanded leafroller, San Jose scale, European red mite, rosy apple aphid and woolly apple aphid in mind at this time of year too. 

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

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