Taking an environmentally sensitive approach to pest management
Over the past several years many spruce trees in Missouri landscapes have been infected by fungal diseases that are disfiguring or fatal. Colorado blue spruce seems most commonly affected, but Norway and white spruce have recently joined the club. In general, spruces are not well adapted to our hot, humid summers.
Until recently, the main problem with Colorado blue spruce has been Rhizosphaera needle cast. The fungus causing this disease generally gains a foothold on lower branches and, if left untreated, can work its way all the way to the top. Older needles on affected trees turn purplish and eventually drop off. Infected needles have many tiny black fruiting structures protruding through the epidermis. Fungicides containing chlorothalonil or copper applied to the new growth during spring and early summer can keep the disease from spreading.
Perhaps due to three successive, abnormally wet springs, other fungal diseases appear to have gained a foothold on spruces in Missouri. Although the causal agents are a topic of discussion among pathologists, one "new" fungal malady is referred to as SNEED (sudden needle drop of spruce). In contrast to Rhizosphaera, needles affected by SNEED do not turn purplish and do not exhibit fruiting bodies. Instead the fruiting bodies appear on the stems and twigs. Affected branches are more randomly arranged within the tree than in the case of Rhizosphaera. If a tree is just beginning to show symptoms of SNEED, pruning out affected branches (during dry weather) and burning dead branches may help reduce the spore numbers. Spraying with a fungicide containing chlorothalonil or copper to protect the developing needles can also prevent further spread. For further information on SNEED see this link: http://na.fs.fed.us/fhp/fhw/csfhw/nov03/sneeddetail.pdf
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REVISED: October 8, 2013