Integrated control of Allium white rot
A. E. FERRY (1), R. M. Davis (2). (1) University of California-Davis, Woodland, CA, U.S.A.; (2) University of California-Davis, Davis, CA, U.S.A.
White rot, caused by the ascomycotina fungus <i>Sclerotium cepivorum</i>, is the most serious disease of <i>Allium</i> food crops world-wide, especially onion (<i>A. cepa</i>) and garlic (<i>A. sativum</i>). <i>S. cepivorum</i> spreads and overwinters as sclerotia, which germinate in response to <i>Allium</i> root exudates. An integrated pest management (IPM) approach is necessary for continued economic production in infested areas. Refining fungicide recommendations and combining them with sclerotia germination stimulants (SGS) (which promote sclerotia germination when no hosts are present) and biological controls are promising methods of disease control. Field studies were conducted to investigate the efficacy of combining SGS with fungicides. When fungicides were combined with an SGS, disease incidence was significantly reduced over either control method alone. By determining EC<sub>50</sub> and EC<sub>80</sub> (Effective Concentration to reduce mycelial growth by 50 and 80%) we were able to determine optimal fungicide concentration in soil, and also screen for fungicide resistance. Using HPLC-MS-ESI we determined the length of time that the most common fungicides remained in the soil root zone, and also determined that their primary mode of activity was inhibition of mycelial growth in the plant root zone. These data, combined with field studies utilizing multiple disease controls, have been instrumental in refining IPM recommendations for the control of Allium white rot.
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