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Plant Pathology - Mike Matheron

My research program is focused primarily on the biology of fungal plant pathogens and the ecology and management of economically important diseases of fruit and nut trees, vegetable and certain field crops that occur in Arizona. The primary goal of this research is to develop new or improve upon existing practical solutions for plant disease problems confronting growers in Arizona.

Two fungal pathogens of citrus are responsible for yield losses as well as death of infected trees. One of these pathogens, Phytophthora, is a soil-borne fungus that infects and destroys root and trunk tissue of citrus trees. Effective disease management strategies have been developed for root rot and gummosis caused by Phytophthora. On the other hand, Coniophora infects the above-ground portions of lemon trees, colonizing and destroying wood tissue. This disease has reached epidemic levels in mature lemon groves in southwestern Arizona. Effective management approaches for Coniophora brown wood have not yet been developed; therefore, a major research effort is directed at studying the biology of the pathogen and the ecology of disease development, so that effective disease control strategies can be formulated.
Several diseases caused by plant pathogenic fungi effect the vegetable industry in Arizona. Downy mildews are important diseases on broccoli, cabbage, cauliflower, lettuce and onions. Powdery mildews can cause significant yield losses on lettuce and melons. Sclerotinia leaf drop is a significant disease problem on lettuce in Arizona and essentially everywhere this crop is grown. The severity of these diseases is greatly influenced by the environment. Downy mildews and Sclerotinia leaf drop are enhanced by cool moist conditions, whereas powdery mildews are favored by a dry and relatively warm environment. Effective management of these diseases caused by fungi involves the integrated use of host resistance as well as cultural and chemical disease control approaches. The use of fungicides is and will likely continue to be an important component of the total disease management tool kit. Many new fungicides are being developed with novel modes of action and with a reduced risk toxicological profile to nontarget organisms. I conduct a comprehensive field testing program each year to compare the efficacy of these new chemistries to established fungicides and to establish effective rates and application sequences on lettuce, broccoli and cantaloupes. 
Nonchemical disease management studies are also in progress. One of these investigations involves the analysis of soil conditions that will promote rapid destruction of the overseasoning sclerotia of the fungi that cause Sclerotinia leaf drop of lettuce. In another long-term experiment, the world peanut collection is being examined to discover potential resistance in this plant to preharvest aflatoxin contamination, a costly and serious food safety problem confronting peanut producers and consumers around the world.
The intent of my outreach activities is to develop and deliver educational programming pertaining to plant diseases and their management to clientele in Arizona as well as to a broader worldwide audience. Effective control of any plant disease involves the development and use of an integrated disease management system. The components of disease management systems are developed from my research as well as information from other sources.
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