WSU Extension

Hortsense

Hawthorn
 
Disease
Fire blight 
Leaf spot 
Rust 
Scab 
Insect
Apple-and-thorn skeletonizer 
Hawthorn aphid 
Pear slug 
Scale insects 
Spider mites 



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Caption: Hawthorn leaf spot
Photo by: R.S. Byther
  
Hawthorn : Leaf spot
(revision date: 2/25/2015)


Biology
Leaf spot is a fungal disease which can infect hawthorn, photinia, pear, pyracantha, crabapple, and related species. Initial infections are small reddish-brown to grayish spots on the upper or lower leaf surface. The spots may enlarge and coalesce on very susceptible species. On hawthorn, the spots are followed by yellowing and premature drop of the affected leaves. A "green island" effect can arise when the leaf turns yellow, as the areas around the fungal lesions may remain green. The disease is favored by wet weather and is easily spread from infected tissues by rain and splashing water. It overwinters mainly on fallen infected leaves. Succulent new growth is particularly susceptible to infection.
Management Options


Non-Chemical Management
  • Plant resistant species such as Crataegus crus-galli (cockspur thorn) and C. phaenopyrum (Washington thorn).
  • Avoid overhead watering.
  • Space plants and prune to reduce humidity and improve air circulation.
  • Pick and destroy infected leaves.
  • Collect and destroy leaf debris beneath infected plants.
  • Use only moderate amounts of nitrogen to reduce amount of succulent new growth. It may help to switch to a slow-release or low-nitrogen fertilizer.
Select non-chemical management options as your first choice!

Chemical Management

Begin applications at bud break and repeat at 7 to 14 day intervals (14-day intervals ONLY for Spectracide IMMUNOX) until conditions are no longer favorable for disease development. 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
  • Spectracide IMMUNOX Multi-Purpose Fungicide Spray Conc
    Active ingredient: myclobutanil  |  EPA reg no: 9688-123-8845
  • This list may not include all products registered for this use.
Images

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Caption: Hawthorn leaf spot
Photo by: R.S. Byther
Caption: Hawthorn leaf spot
Photo by: R.S. Byther
Caption: Hawthorn leaf spot
Photo by: R.S. Byther