Effect of source and rate of manures on incidence and severity of important diseases, yield and yield components in cotton (Gossypium hirsutum L.)

To evaluate the effect of manures on the damping-off, Alternaria leaf spot (ALS), Verticillium wilt (VD), yield and yield components of cotton, a field experiment was carried out at Cotton Research Station of Kordkoy (35 km west of Gorgan,), Iran, with silty-loam soil and histories of soil-borne diseases including; seedling diseases (Rhizoctonia solani, Pythium ultimum, Fusarium spp.) and Verticillium dahliae, in 2004-06 growing seasons. Three sources of manure (cow, sheep and poultry) and four manure levels (0, 10, 20 and 30 tons.ha-1) were arranged in a 3×4 factorial experiment using randomized complete block design with four replications. The results showed that the effect of source (S) and rate (R) of manures were significant on seedling emergence, length of 5th sympod, boll weight (BW), yield, VD and ALS, No. boll.plant-1, post-emergence damping-off, and ALS severity. The S×R interaction was significant on BW, No. boll.plant-1, seedling emergence, yield and i diseases incidence. Application of poultry manure (PM) increased cotton yield and decreased damping-off and verticillium wilt diseases. Among animal manures sources and levels 20 tons.ha-1 of PM had the most seedling emergence and the least seedling diseases. However, the highest and lowest Alternaria leaf infection were scored in 10 tons.ha-1 of PM and 30 tons.ha-1 of cow manure (CM), respectively. The 30 tons.ha-1 of CM had also the lowest disease severity. The greatest verticillium wilt incidence and severity was scored in 30 tons.ha-1 of PM and the highest wilt infection and disease severity index were scored in 10 tons.ha-1 sheep manure (SM) and 10 tons.ha-1 of CM, respectively. In conclusion, application of poultry manure in the infected cotton field to the verticillium wilt improved agronomic performance and yield of cotton as well as reduced verticillium wilt incidence and severity.