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Assessment of Benefits of Cotton Seed Dressings for the Control of Seedling Diseases in Relation to Inoculum Densities of Pythium and Rhizoctonia

R.M. Davis, J.J. Nunez, K.V. Subbarao


Twenty-five field trials (each with 6 or 8 replications) conducted over a three year period in five San Joaquin Valley counties included the following treatments: nontreated seed (cultivar Maxxa); seed treated with myclobutinol (NuFlow M) for the control of Rhizoctonia-induced damping-off; seed treated with metalaxyl (Apron) for the control of Pythium-induced damping-off; and seed treated with a combination of the fungicides. The following parameters were measured: healthy stands from each treatment, soil populations of Pythium spp. and Rhizoctonia solani at planting, soil temperature at planting, air temperatures for five days after planting, soil particle analysis, EC, calcium, pH, and organic matter. In 1993 and 1994, myclobutinol and the combination of the fungicides resulted in improved stands in 14 of 18 fields. Metalaxyl did not increase stands with the exception of one field, where it significantly increased stands but not to the degree of the myclobutinol treatment alone or in combination with metalaxyl. In three fields in 1993-4, no treatment significantly increased stands. In 1995, the combination of fungicides increased stands relative to the nontreated seeds and was more effective in increasing stands than either myclobutinol or metalaxyl alone. Pythium populations were much greater in 1995 than in 1993-4 and may explain the beneficial, synergistic effect of the fungicides. Covariate analysis of all the data indicated no relationship between stand increases due to the fungicide seed treatment and any soil parameters. Heat units following planting were not limiting and had no effect on stands. Benefits of fungicides were not influenced by pathogen populations with the exception of a negative correlation between stand increases due to seed treatment with myclobutinol and Pythium populations. Apparently, seed treated with myclobutinol are more susceptible to infection by Pythium spp. Overall, the myclobutinol seed treatment increased cotton stands regardless of soil type and pathogen population. There were small benefits from the metalaxyl seed treatment.

Reprinted from Proceedings of the 1996 Beltwide Cotton Conferences pp. 267 - 268
©National Cotton Council, Memphis TN

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Document last modified Sunday, Dec 6 1998