Chemical and Cultural Management of Black Root Rot of Cotton Caused by Thielaviopsis basicola

J.E. DeVay, S. El-Assar, R.J. Wakeman, and R.H. Garber


Black root rot caused by Thielaviopsis basicola (TB) has become a serious problem in cotton production in California since about 1980. Cool soil temperatures, unfavorable for seedling development, favor the infection and rotting of cortical tissues of cotton roots by TB. During extended periods of cool soil temperatures, seedlings may not recover, and if they do, the resulting plants are often stunted, slow to develop, and yields of lint may be reduced. Chemical seed treatments have not been effective in controlling black root rot in the field although some have shown promise in greenhouse tests; among these seed treatments, Baytan [ -(4-chlorophenoxy)- -(1,1-dimethylethyl)-1H-1, 2,4-triazole-l-ethanol] has been most effective for control of TB. Baytan is also highly effective in controlling damping-off caused by Rhizoctonia solani and in combination with Apron [N-(2,6-dimethenyl)-N-(Methoxyacetyl)-alanine methylester] shows excellent promise to manage seedling diseases of cotton in the field. Seed treatment rates for Baytan 30F as low as 1.5 oz formulated material/cwt of seed have been effective, although higher rates up to 3 oz/cwt are recommended for soils heavily infested with TB. Stunting of plants by Baytan has been observed at rates over 6 oz/cwt of seed. Based on grower observations, flooding of soil and rotations with onions are cultural practices which have shown promise of controlling black root rot. Greenhouse experiments have confirmed the effectiveness of these practices. In soil infested with approximately 198 propagules of TB/gm soil, flooding soil for 4 weeks at greenhouse temperatures of 20 to 25 C, reduced the propagule density by over 95% whereas in soil infested with approximately 198 propagules/gm soil, the reduction after 3 weeks of flooding was 45%. In both tests, the severity of black root rot in following plantings of cotton (Acala SJ-2) was significantly reduced. Similar reductions in black root rot were observed in cotton plants following growth of garlic or red onions in soil infested with TB at both 198 and 317 propagules of TB/gm soil. The tests were repeated twice with three replications of 120 cotton plants per replication.

Reprinted from 1990 Proceedings: Beltwide Cotton Production Research Conferences pp. 37 - 38
©National Cotton Council, Memphis TN

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Document last modified Sunday, Dec 6 1998