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item Howell, Charles - Charlie

Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Abstract Only
Publication Acceptance Date: 1/5/2004
Publication Date: 2/21/2004
Citation: Howell, C.R. 2004. Cotton seedling disease control with biological/chemical seed treatments. Proceedings of Beltwide Cotton Conferences. January 5-9, 2004, San Antonio, Texas. National Cotton Council. 2004 CDROM. p. 421.

Interpretive Summary:

Technical Abstract: The pre-emergence phase of cotton seedling disease, incited by Pythium spp. and Rhizopus oryzae, is very effectively controlled with biocontrol strains of Trichoderma virens. However, they are much less efficient in the control of the post-emergence phase of the disease that is incited by Rhizoctonia solani. The post-emergence phase of the disease can be successfully controlled with systemic fungicides. Control of both pre-and post-emergence cotton seedling diseases will therefore most likely require combination seed treatments of biologicals and chemicals. The purpose of this study was to determine the disease control efficacy of various biological/chemical combination seed treatments, in soil infested with pre-and post-emergence damping-off pathogens, in an effort to discover the most effective means of controlling both phases of cotton seedling disease. Black seeds of the cotton cultivar DP 451 B/RR were treated with the recommended concentrations of the seed treatment fungicides Baytan, Chloroneb, Deltacoat AD, Dividend, Flint, Maxim, Nuflow M, Vitavax, or Vitavax-PCNB. Non treated or fungicide treated seeds were then coated with latex and dry Wheat bran + Peat moss granules of Trichoderma virens strain G-6. Non treated, fungicide treated, or fungicide + G-6 treated seeds were planted in test tubes containing 10 grams of moist field soil naturally infested with pre-emergence damping-off pathogens, or infested field soil amended with air dry millet culture granules of Rhizoctonia solani. The tubes were incubated in a growth chamber at 25 degrees C and with a 14 hr photoperiod. After 7 days incubation, the tubes were examined for the presence of emerged and surviving seedlings. The resulting data were analyzed using SAS. Planting black cotton seed of the cultivar DP 451 B/RR in naturally infested field soil resulted in 0-10% seedling survival. Seed treatment with the fungicides tested in this trial resulted in very little improvement in seedling stand, with % survival ranging from 7-13%. However, seed treatment of DP 451 B/RR with WB+PM preparations of the biocontrol strain G-6 of Trichoderma virens significantly improved seedling stands over the fungicide treatments and the non treated control, and seedling survival was increased to 93%. Stands of non treated cotton seedlings planted in naturally infested field soil amended with R. solani were also devastated, with 0% survival in the soil. Again, seed treatment with the fungicides tested did little to alleviate the disease syndrome, with % survivals ranging from 0-20%. Seed treatment with the biocontrol agent alone resulted in significant improvement over the non treated control and the fungicide treatments. However, seedling survival was still only 40% of the seed originally planted. The numbers of emerged and surviving cotton seedlings from field soil naturally infested with Pythium spp. and Rhizopus oryzae, and amended with Rhizoctonia solani, was vastly improved by chemical/biological combination seed treatments. Some of the combination treatments were far superior to either the fungicide or the biocontrol agent alone, while other combinations were no better than the individual treatments. The most effective combinations were Chloroneb + G-6 and Deltacoat AD + G-6, followed in descending order by Vitavax + G-6, , Vitavax-PCNB + G-6, Flint + G-6,Baytan + G-6, , Nuflow M + G-6, Maxim + G-6 and Dividend + G-6. Planting the seed of disease susceptible cotton cultivars in soil infested with seedling disease pathogens can result in devastating reductions in plant stand. In soil where only pre-emergence damping-off pathogens such as Pythium spp. and Rhizopus oryzae are present, seed treatment with strain G-6 of Trichoderma virens can effectively control disease. The mechanisms employed by the biocontrol agent to control this phase of the disease syndrome are; 1) metab