Many evergreen samples have been submitted to the Plant Disease Clinic during the month of March. Samples submitted have included concolor fir, white pine, mugo pine, Scots pine, blue spruce, white spruce, arborvitae and hemlock. In most cases, needles show a yellow to brown color, often on the entire tree.
The symptoms appear to be related to last year's dry conditions. Conifers also continue to lose moisture from their needles during the warm, windy days of fall and winter.
Infectious disease problems may also cause browning of needles. Needle blights of Austrian and Scots pine have been observed as well as Rhizosphaera needle cast on spruce. A close look at the needles can help distinguish infectious diseases from environmental stresses. Pm-1528 "Common Diseases of Conifers" contains color photos of disease symptoms.
Infectious diseases such as Dothistroma needle blight, brown spot, and Rhizosphaera often progress over the years from lower branches to upper branches. Red or brown spots or bands are evident on infected pine needles. A close look (hand lens is helpful) at infected spruce needles will show small black fruiting structures of the fungus in the pore-like openings of infected needles.
Steps can be taken to control infectious needle diseases of conifers, primarily with protectant fungicide sprays in the spring as the new needles are emerging. Pm-1528 highlights timing and labeled products.
This article originally appeared in the April 7, 2000 issue, p. 27.