Graduate Thesis Or Dissertation
 

Epidemiology of Lophodermella morbida in plantations of ponderosa pine in western Oregon

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/nk322h588

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  • In 1967, Lophodermella morbida Staley and Bynum, a recently described hypodermataceous needle-cast fungus, became destructively epidemic in a knobcone pine (Pinus attenuata Lemm.) plantation in Del Norte County, California, and in several ponderosa pine (P. ponderosa Laws.) plantations in western and southwestern Oregon. This thesis presents information on this currently destructive disease. The life cycle of L. morbida is completed within 12 months. Mature ascospores are discharged during periods of general rain from early June through mid-July. Infection occurs only on foliage recently emerged from the fasicle sheath. Foliage infected in one year drops from the tree by mid-summer of the next. By midsummer about one-half of each newly infected needle has become necrotic; thus seriously impairing food production. Growth of repeatedly infected trees is significantly reduced; however, from 1969 through 1973, there has been little mortality in the plantations under study. Probably L. morbida is a native fungus, catapulted to prominence in populations of a very susceptible host growing on unsuitable sites under climatic conditions favoring spread of the pathogen and disease intensification. To avoid trouble from this disease, planting ponderosa pine on questionable sites should be stopped. When ponderosa pine is planted, ridgetops and natural basins where clouds linger should be avoided. On the eastern slope of the Cascade Mountains, the risk from L. morbida to either natural stands or plantations of ponderosa pine appears minimal because of limited moisture. However, an unusually wet June or July might substantially increase the risk. Pine on the windward (west) slope of interior mountains of the Pacific Northwest may have a high risk factor from infection because of favorable rainfall patterns induced by local topography.
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