WSU Extension

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Caption: Fruit russeting on plum
Photo by: R.S. Byther
  
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Plum, Prune (Fresh) : Russeting
(revision date: 9/12/2016)


Biology
Russeting of plum can be caused by several factors. Rain during the period of full bloom, mechanical rubbing against other fruit or branches caused by wind, or other injury of the (russet scab) fruit surface can result in russet symptoms. High winds following full bloom and copper fungicide applications are other causes of russeting on French prunes. Affected fruit initially show shiny areas on the surface where normal wax is lacking. The shiny area develops into a brown, corky or scabby area just before fruit harvest. Affected fruit may be misshapen. Thrips may cause similar russeting symptoms on all stone fruits.
Management Options

Non-Chemical Management
  • Avoid overhead watering during bloom and petal fall.
Select non-chemical management options as your first choice!

Chemical Management


Though no fungal or other microorganisms have been associated with russet scab, fungicides applied during the bloom period control the problem. A yeast has been associated with russet on pome fruit. Russeting caused by wind or thrips would not be managed with fungicide applications. Homeowners should not make foliar applications to trees over 10 ft tall. Consult a commercial pesticide applicator for treatment of trees and shrubs over 10 ft. tall.

Listed below are examples of pesticides that are legal in Washington. Always read and follow all label directions.
  • Bonide Fung-onil Multi-Purpose Fungicide Conc
    Active ingredient: chlorothalonil  |  EPA reg no: 60063-9-4
  • GardenTech Daconil Fungicide Conc
    Active ingredient: chlorothalonil  |  EPA reg no: 67572-82-71004
  • Ortho Max Garden Disease Control Conc
    Active ingredient: chlorothalonil  |  EPA reg no: 239-2522
  • This list may not include all products registered for this use.
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Caption: Fruit russeting on plum
Photo by: R.S. Byther