Infectious needle diseases of conifers, such as Dothistroma needle blight on Austrian pine, brown spot of Scots pine, and Rhizosphaera needle cast of spruce are controlled primarily through the use of protectant fungicide sprays in the springs. The first spray is typically applied around mid-May and a second application a month later.
Color photos of these diseases appear in Pm-1528 Common Diseases of Conifers in Iowa. An accurate diagnosis of a disease problem is important. Fungicide sprays will be useless on a tree that is showing browning related to environmental injury such as winter burn.
This article originally appeared in the May 9, 1997 issue, p. 62.