The loss of dying pima cotton after a rainfall in August 1987 made apparent the different responses pima and upland cottons have to stress. A trial compairing pima S-5 and DP 77 found more response of pima to treatment of rootknot nematodes with 1,3-Dichloropropene than the upland variety. A second trial found more response of DP 77 to 1,3-Dichloropropene treatment than from fenamiphos injection on sandy loam.

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Two years after sterilizing a sandy loam soil in Marana, we measured significant yield responses of short staple cotton. The yield response was significant in the first year as well, but was not enough to pay the cost of sterilization. This second year of yield response made the treatment economically feasible.

Incidence of Black Root Rot of cotton and soil inoculum potential of the causal agent Thielaviopsis basicola were monitored throughout the season in two adjacent fields planted in mid April, 1987 in Duncan, Arizona. Mean inoculum potential in Field 1 soil was 65 cfu/g and 20 % of the seedlings were infected. In Field 2 the inoculum potential and percentage of infected plants were 225 cfu/g and 93, respectively. No cortical decay was noted after June 6 in either field. Yields were similar in both fields.

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Experiments were performed at the Yuma Valley Agricultural Center to determine how timely harvest of cotton may affect aflatoxin contamination of cottonseed As the cotton was held in the field between the final irrigation and harvest, the quantity of aflataxin in the crop increased. Significant reductions in aflatoxin contents of seed were realized by harvesting in early September.

High population levels of Rhizoctonia solani in a field in Coolidge, AZ which also contained Thielaviopsis basicola failed to cause the expected infection by R. solani in untreated seeds of Gossypium hirsutum. Growth chamber experiments with autoclaved soil amended with inoculum of both R. solani, and T. basicola had a significantly lower infection rate by R. solani than did the control soil with R. solani alone.

Mapping aflatoxin contamination in the field reveals that most toxin occurs in relatively few, highly contaminated, bolls. Several studies suggest that protection of early bolls from pink bollworm damage will eliminate many of these highly contaminated bolls. Early harvest will also help reduce aflatoxin contamination. However, the crop must still be carefully managed after harvest because toxin content of mature bolls can increase very rapidly.

The overall goal of our study is to find effective and environmentally sound methods to reduce pre -harvest aflatoxin contamination of cottonseed in Arizona. The specific objectives are: 1) to screen a large number of bacteria for their ability to destroy the aflatoxin producing fungus, Aspeigillus flavus; 2) to test the efficacy and consistency of the recovered antagonistic bacterial isolates to reduce aflatoxin contamination of cottonseed in field trials; 3) to study the survival and competitiveness of the antagonists on cotton plants under prevailing field conditions; 4) to find innovative procedures to enhance survivability and competitiveness of the antagonists on cotton plants; and 5) to test the potential of the bacterial antagonists to reduce the population of A. flavus in field soils. Over 800 bacterial isolates, recovered from cotton field soils, cotton leaves, stems, and immature as well as opened bolls, were tested for ability to inhibit the growth of A. flavus on cottonseed. Six isolates partially or totally inhibited the fungus. All of these effective isolates prevented the fungus fioin infecting simulated pink bollworm exit holes in immature bolls in the field.

A serious virus disease of cotton in Pakistan is distantly related to cotton leaf crumple in Arizona. It is much more destructive on cotton than leaf crumple, and has never been found in the western hemisphere. Cotton leaf crumple in Arizona causes only modestly damaging midseason infections, while leaf curl, has had a major impact on the crop in Pakistan. Modern transportation and the increasing movement of living plants in global trade has resulted in them recent introduction of a similar disease of another crop to the western hemisphere.