It's not hard to find a good case of Dothistroma needle blight in Iowa. It's a common disease problem on Austrian pine. The fungus Mycosphaerella pini is responsible for the disease.
Dothistroma needle blight is fairly easy to diagnose; specialized laboratory equipment is not needed. Early symptoms consist reddish-brown spots or bands on needles. The ends of infected needles eventually turn brown from the banded area outward, with the base of the needles remaining green. (Winter injury may also cause browning of needle tips, but spots and bands are not evident.)
Within a few weeks after the needles die, small black fruiting structures of the fungus break through the outer needle tissue (epidermis). Infected needles drop prematurely, with the lower branches usually showing early loss of needles first.
The primary means of disease control is the use of fungicide sprays (Bordeaux mixture or other copper-containing fungicides) in the spring when the new growth is emerging. The first spray is applied about mid-May and a second application in mid-June. Because of its susceptibility to needle and tip blight diseases, Austrian pine is no longer a recommended pine species for planting in Iowa.
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 April 3, 1998 issue, p. 31.