Two planting dates, March 28, and April 28 were used to study the effect of soil temperature during planting on black root rot of cotton. Also, several cotton varieties were evaluated for response to the disease under varying soil temperatures and inoculum levels.

Eight short staple varieties were evaluated for severity of symptoms, percent of plants infected and yield while being grown in a Verticillium nursery on the Safford Agricultural Center. Delta Pine 90 showed the least severe symptoms, had the least number of infected plants and also yielded the highest. Another Delta Pine variety, DP 77, showed moderate symptoms and a 96% infection rate, but it still managed to come in third in yield, only 49 pounds per acre behind DP 90. Yield potential and varietal adaptability must be considered along with Verticillium wilt resistance in deciding what variety to plant, even in a field infested with Verticillium.

Residual effects from methyl bromide applied in 1986 showed increased yields in 1987. Increases from 115 to 281 pounds of lint per acre were observed, depending on the rate applied in 1986. This residual effect increases the possibility that this soil sterilant will be a useful tool to combat Texas root rot. Differences were also noted between 1986 and 1987 applications.

Methyl bromidelchloropicrin, a soil sterilant, was deep-injected into cotton beds ten days before planting. Within the kill areas of the Texas Root Rot, the soil sterilant had some significant effects on the mortality and yield of the cotton.

Weather conditions leading to the development of southwestern rust on cotton were evaluated at 3 locations in southeastern Arizona. Rust appeared following an extended period of wet, humid weather. In excess of 16 hours of wet canopy/high humidity conditions were observed on two consecutive days between 5 and 7 days prior to the appearance of rust. Temperatures during the wet canopy/high humidity periods were moderate, ranging from 65 F to 76 F. Afternoon rain showers initiated these extended periods of wet canopy /high humidity conditions.

Cultivars and germplasm lines of cotton, Gossvpium hirsutum L., differed in response to infection by the cotton leaf crumple virus (CLCV). The most widely grown cultivars in Arizona and southern California, 'Deltapine 90' and 'Deltapine 61', are susceptible, while ' Cedix', developed in El Salvador, and 'Coral', developed in Nicaragua, are highly resistant or immune. Nineteen other lines from a resistance breeding project in Nicaragua showed highly variable responses.

Methyl bromid/chloropicrin formulations were applied to strips in the verticillium nursery at the Safford Agricultural Center where two varieties of short staple cotton were subsequently planted. More robust plant growth and reduced incidence of disease were noted with some of the treatments. Yield increases over the check plots were also seen. A study of the residual effects of the treatments will be performed in 1989.

Aflatoxin contamination of cottonseed from bolls damaged by the pink bollworm was compared with contamination of cottonseed from undamaged bolls. Cottonseed produced in pink bollworm damaged bolls was the predominant source of aflatoxin contaminated cottonseed.

Methyl bromid/chloropicrin, a soil sterilant, was deep injected into cotton beds 10 days before planting in 1987. The 1987 cotton lint yields were significantly increased by injecting the sterilant into the Texas root rot kill areas. Cotton yield and mortality data were taken in the same plots in 1988 to measure the carry-over of the treatments. Lint yields trended higher and plant mortality trended lower in the sterilant- treated plots, but no significant differences were detected.

Methyl bromide/chloropicrin (MB/C), a soil sterilant, was deep injected into cotton beds 6 days before planting in 1988. Application rates were zero, 300, 400, and 500 pounds of MB/C per acre, injected 18-inches deep into the sandy loam soil. Short staple lint yields in all of the MB/C treatments were significantly higher than the untreated check. MB/C at all application rates was 100% effective in preventing the plants from dying from the disease, while 86% of the plants in the untreated check plots died.