From field investigations and inoculations,Dothistroma pini,the pathogen ofDothistroma needle blight was found to overwinter as mycelium and unmatured acervuli in infectedneedles.The conidia were spreaded mainly by rain splash.The disease became widespread by trans-porting discased seedlings and seions conidia spread throughout the growing season,but mainlyfrom May to July.The diseade was found in both stand locations in each summer of investigation.The outbreak severity was serious in pure stands of susceptible pine and mixed stands with largecomponents of suseeotuble pine.but slight in mixed stands of unsusceptible species with small com-ponents of suseeptible hosts.The disease was less severe in pruned stands than in unpruned stands.The disease was most serious near the infection centre.indoor and outdoor tests,it was shown thatChlorothalonil smoke,Chlorothalonil spray and Thiram and Asomate sprays were effective controlfungicides.
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