Thornless Hawthorn tree berries

Asked July 28, 2016, 5:52 PM EDT

My 15 year old (about) Thornless Hawthorn has many berries that are covered with a dusty brown fuzz this year. There may have been fruit like this in previous years but I don't remember so many, and the leaves are not as full as previous years. Is there something wrong with the tree? If so how do I treat it?

Hennepin County Minnesota

1 Response

It appears that your Thornless Hawthorn tree may be infected with a Gymnosporangium Rust either Hawthorn or Quince Rust. Since Quince Rust primarily attacks the fruit and tender stem growth as opposed to Hawthorn Rust which produces leaf lesions and rarely produces orange to rust colored spore-filled blisters on the fruit surface, your tree is probably infected with Quince Rust. Fruit infected with Quince rust are covered with protruding aecia of the fungus.

Both cultural and chemical controls are necessary in dealing with this problem. According to the University of Minnesota extension, If applied before infection occurs, protective fungicides can be used to control the disease on Rosaceae plants like the Thornless Hawthorn. Typically, this occurs when flower buds first emerge and continues until spring weather becomes consistently warm and dry. Nearby infected junipers can be monitored and fungicides applied when gelatinous orange spore producing structures appear on galls and branches. Chemical treatments should have listed the following active ingredients include.

    • Myclobutanil- most effective!
    • Copper
    • Sulfur
Proper cultural practices are still the cornerstone of any management program to help trees and shrubs deal with stresses imposed by insect and disease attack. The University of Minnesota Extension recommends the following practices:
  • Do not plant eastern red cedar and juniper plants within a few hundred yards of susceptible Rosaceae plants. This will reduce but will not completely eliminate disease problems.
  • Prune and remove brown woody galls found on the eastern red cedar and juniper plants before orange gelatinous spore producing structures form in spring to reduce the level of infection on nearby Rosaceae plants.
  • Prune and remove infected twigs or branches on Rosaceae plants when they occur.
Below are links to the University of Minnesota Extension website that provide more information about these diseases: