Graduate Thesis Or Dissertation
 

Postemergence herbicides and take-all disease in winter wheat : alterations in the incidence and severity of disease and crop growth

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  • Eight postemergence herbicides were evaluated to determine their influence on the incidence and severity of take-all disease caused by the fungus Gaeumannomyces graminis var. tritici in winter wheat. Mecoprop ((+)-2-(4-chloro-2-methylphenoxy)propanoic acid), difenzoquat (1,2- dimethyl- 3,5- diphenyl -1H- pyrazolium), dinoseb amine (amine salt of 2-(1-methylpropy1)-4,6-dinitrophenol), and diclofopmethyl (methyl ester of (+)-2-[4-(2,4-dichlorophenoxy) phenoxy]propanoic acid) sometimes reduced the severity of take-all disease on the seminal and crown roots. The herbicides also reduced the incidence of 'whiteheads' associated with take-all injury. In additional evaluations, mecoprop, difenzoquat, and dinoseb did not affect severity of disease on the roots, but whiteheads again were reduced. Diclofop-methyl applied at 1.12 kg ai/ha in early January often reduced the severity of take-all disease on seminal and crown roots. Higher rates of this herbicide, however, occasionally increased disease severity. The number of seminal roots produced by plants treated with diclofop-methyl often depended upon both application rate and the level of take-all stress. Crown root and tiller production were stimulated by diclofop-methyl. Low rates of difenzoquat, dinoseb, and mecoprop often increased tillering as well. The responses of the wheat plant to all four herbicides generally were greatest in plots with take-all disease. Fresh weights of individual tillers generally were reduced in response to herbicide application. Stimulations of tillering in diseased plots treated with diclofop-methyl progressively declined when applications were delayed after early January. Grain yields were greater in diseased plots treated with mecoprop, difenzoquat, and dinoseb than in the untreated check in 1982. Grain yield was either reduced or unaffected by diclofopmethyl, regardless of the level of take-all disease present. Herbicides did not affect grain yield in 1983. In vitro growth of three isolates of Gaeumannomyces graminis var. tritici was not inhibited by diclofop-methyl at concentrations below 10 ,uM. Data suggest that herbicides reduced take-all disease by altering wheat growth, allowing diseased plants to compensate for take-all injury. Susceptibility of root tissues to infection also may have been reduced in some cases.
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file details GeddensRayM1986.pdf 2017-10-19 Pubblico Scaricare