Both ornamental and eating apples (Malus spp.), some mountain ash (Sorbus spp. ), cotoneasters (Cotoneaster), Hawthorn (Crataegus) and common pear (Pyrus ).
- Occurs during periods of moderate (2 – 26 °C) temperatures and very high humidity in spring and early summer.
- Infection caused by spores that are carried by wind and rain.
- Leaves may appear yellowed, curled, puckered, with brownish lesions over both sides of the leaf.
- Fruit may exhibit dark raised lesions and distorted growth.
- Both fruit and leaves may fall prematurely, which can make the tree more susceptible to winter damage.
- Mature tissues may be resistant to infection yet still harbor spores that can re-infect other tissues.
- Yield and quality of harvest is reduced.
- Spores can overwinter in previously infected tissue such as leaves, fruits, flowers, and twigs.
Use a fruit-tree copper or sulphur spray fungicide. In the fall, make sure to clean away all debris that can be harbouring the spores for re-infection next spring. Apple scab will not kill your tree if left untreated, however it is very unsightly and reduces the quality of fruit, as well the lack of control in one yard can lead to infestation of surrounding yards.
Compiled by: Dr. Bill Paton and Jennell Rempel