2024 May Bring Fire Blight Challenges to Midwest Orchards

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Suzanne Slack
Fruit Crops Specialist
Iowa State University Extension and Outreach
slacksuz@iastate.edu

 

The rainy, warm spring this year in Iowa might be problematic for orchards due to fire blight. Conditions for most of Iowa were nearly perfect for the disease to spread, resulting in potential surprise flare ups. Fire blight can be devastating, especially for immature apple and pear trees which may die within the same year of infection. Scouting for strikes is important for the overall health of your orchard as some practices, like nitrogen fertilization, will cause trees to be more susceptible to fire blight

Symptoms to Watch For:

Blossom Blight: Flowers and small fruits appear burnt, turning orange and then black; typically, it is most noticeable a few weeks after full bloom.

Ooze Droplets: Colorful droplets may form on fruit and leaf stems, spreading to nearby shoots.

Shepherd’s crook: Shoots will turn orange to black and flag, resembling a shepherd’s crook.

What to Do:

Early Detection: Scout for flagging shoots and fruit clusters. With how wet it has been the shoots may not flag until a dry or hot spell.

Immediate Action: Swiftly remove blighted fruit and shoots. Cut at least 12 inches below the infected area to prevent further spread, as the bacteria travel internally faster than the symptoms appear.

There are several commercial pesticide products labeled for shoot blight, the second stage of the disease. These products work by causing a defense response in the tree to prevent further spread. Because of this mode of action, it takes 10 to 14 days for plants to be less susceptible to disease. A favorite is Apogee or Kudos (Prohexidione-calcium). At low rates tank mixed with Actigard, it can be used on young trees with no significant growth defect. See page 49 of the Midwest Fruit Pest Management Guide (free online from Purdue Extension) for more information on Apogee for shoot blight management.

Streptomycin resistance

The fruit disease program at Iowa State has confirmed streptomycin resistance in Iowa fire blight outbreaks. For the summer of 2024, the Slack and Yuan Fruit Disease Program is offering free streptomycin resistance screening. If you have used streptomycin but still see active infections, please contact Suzanne Slack at slacksuz@iastate.edu for how to participate.

- Picture of a fire blight infected apple flower one month after blooming. Note the start of shoot blight due to bacterial spread.

Date of Publication: 
May, 2024