Cause Marssonina sp. are fungi that have been reported from all states; M. kriegeriana was reported from Washington, and M. rubiginosa has been reported from Idaho. These fungi overwinter on fallen leaves and in twig lesions. The disease is widespread and common, especially in moist spring weather. It can make trees unsightly but rarely damages tree growth significantly.
Symptoms Usually small, brownish to black, irregularly shaped spots or lesions develop on leaves and twigs. Spots may have white centers. Especially on twigs, spots may coalesce to form large lesions, which may girdle and kill the twigs.
Cultural control
- If practical, prune out and destroy dead and diseased twigs.
- Rake up and destroy fallen leaves during the growing season, especially in fall.
Chemical control Use during early spring growth.
- Protect DF at 1 to 2 lb/100 gal water plus 2 to 4 oz spreader-sticker. Group M3 fungicides. 24-hr reentry.
Reference Hill, J.T., Ormrod, D.J., and Copeman, R.J. 1977. Weeping willow blight in coastal British Columbia. Canadian Plant Disease Survey 57:71-74.