Austrian pines are particularly susceptible to Dothistroma needle blight. Austrian pines showing this disease arrive frequently in the Plant Disease Clinic. The causal organism is the fungus Mycosphaerella pini.
This needle disease can be diagnosed quite easily. Reddish brown spots appear on infected needles in the fall. These needles then turn brown at the tip and drop prematurely, usually the year following infection. Black fruiting structures of the fungus (acervuli) eventually push through the outer needle tissue (epidermis) in the brown necrotic tips or in the needle spots.
The disease is commonly most severe on the lower branches and gradually works upward. Early loss of needles from this disease eventually contributes to poor tree growth. Loss of needles can also lead to branch death or tree death.
A fungicide spray program, such as with a copper fungicide, can protect trees from infection. Proper timing and good coverage are critical. Two sprays are applied, with the first in mid-May and a second spray a month later. This protects the needles from the previous year and the newly emerging needles.
Because Austrian pines are commonly troubled with Dothistroma needle blight and also the fungal disease Diplodia tip blight, they are no longer recommended as a species for planting.
Photos of Dothistroma and other conifer diseases can be found in Pm-1528 "Common Diseases of Conifers in Iowa". This bulletin is available from your local county Extension office or from the Extension Distribution Center (515) 294-5247. The charge is $1.50.
This article originally appeared in the March 5, 1999 issue, p. 19.