Is it winter damage or needlecast?
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Several problems that we are finding are winter damage, Swiss and Rhabdocline needlecast. To tell the differences, look on the underside of the needles. With winter burn you have a drying of the needles that causes the tips or the whole needle to be brown but the stomata (tiny pore-like openings) will be white. If you are seeing two rows of fuzzy, black fruiting bodies coming out of the stomata on green, yellow and brown needles, it probably is Swiss needlecast. Rhabdocline infected needles will appear as yellow to purple-brown splotches (mottling).
Of these two diseases, Rhabdocline is the more serious and can cause serious disease on seed sources San Isabel, Lincoln and Coconino; the seed source Shuswap is resistant to Rhabdocline needle cast. Left unchecked, Rhabdocline needle cast can cause devastating amounts of casting if not managed through genetic, horticultural and chemical programs. Rhabdocline is more severe along Lake Michigan and has recently become severe in inland locations where conditions favor moisture retention on needles in the spring. Swiss needle cast is more wide spread than Rhabdocline in Michigan, but less severe than Rhabdocline unless left unmanaged. Both diseases are currently managed with chlorothalonil-based materials after the new growth has expanded to to 0.5 to 2 inches in length, typically in May.
Dr. Fulbright's work is funded in part by MSU's AgBioResearch.
