Three cotton cultivars (DPL 41, 90 and 775) were planted at 3 seeding rates (5, 10 and 20 lbs/A). These variables were evaluated under 5 drip irrigation treatments, which included 23.3, 25.7, 28.0, 30.7 and 31.4 inches of water applied over the growing season. There were 3" of precipitation over the growing season. Only the lowest irrigation level showed significantly reduced yields. DPL 90 had superior yields as compared to DPL 775, with DPL 41 having an intermediate response. The 10 lb/a seeding rate resulted in higher yields as compared to the other 2 rates.

Three cotton cultivars (DPL 41, 90 and 775) were planted at 3 seeding rates (5, 10 and 20 lbs/A). These variables were evaluated under 5 fertilizer treatments which included increasing nitrogen levels and one treatment with nitrogen (N), phosphorus (P), potassium (K) and zinc (Zn). Residual soil N was high and variable and no clear response to applied N was found, although generally higher yields were found with the high N rate. The plots receiving P, K and Zn yielded less than plots receiving an equal amount of N. Increased seeding rates significantly increased yields which was probably an effect of early weed competition. Delta Pine 90 produced significantly more than 41 which was greater than 775. Petiole and soil nitrate values reflected the high and variable available soil N.

No description available.

No description available.

No description available.

The Crop Water Stress Index (CWSI) was used to schedule irrigations on drip irrigated cotton research plots in Tucson and on eight acre furrow irrigated fields at the Marana and Maricopa Agricultural Centers. Scheduling irrigations when plots reached 0.30 CWSI units resulted in highest yields with 1403 lbs/acre cotton lint using 33.8 inches of water. The Marana and Maricopa fields yielded 1322 lb/acre on 28 inches and 1767 lb/acre on 58 inches of water, respectively.

A quantitative technique has been developed to assay cotton soils for populations of Thielaviopsis basicola, a soil occurring fungus that causes the seedling disease of cotton known as Black Root Rot. The procedure utilizes a soil dilution technique with a carrot extract agar containing etridiazol, Mystatin, streptomycin sulfate, chlortetracycline, calcium carbonate and PCNB. Populations of the fungus have been monitored from April to December, 1986 in a heavily infested Pima S-6 field in cooperation with Bob Cockrill, a Coolidge grower. When field soils containing approximately 600 propagules of the fungus per gram of air dry soil were planted to Pima S-6 in the laboratory, 75-100% and 50-75% cortical decay occurred at 20 and 28 C, respectively. This seedling damage was related to subsequent reduced seedling vigor.

Application of two systemic fungicides, propiconazole (Tilt) and triadimenol (Summit), through subsurface drip irrigation resulted in a significant reduction in the number of dead plants in a Phymatotrichum-infested cotton field. The percent reductions in Tilt treatments were 72% in 1985 and 66% in 1986 and in Summit treatments were reduced 90% in 1985 and 70% in 1986.

Greenhouse techniques were developed to evaluate cotton cultivar susceptibility to Alternaria leaf spot. Results indicate that Deltapine Acala 90 is more susceptible to Alternaria leaf spot than other Gossypium hirsutum varieties tested but that it is less susceptible than the G. barbadense varieties Pima S-5 and Pima S-6.

During the past two years we developed an egg sampling plan for the pink bollworm (PBW) to provide a more accurate index of moth (target stage) activity than conventional larval sampling. The plan requires that only the presence or absence of eggs laid on bolls be determined to decide when insecticide treatments are needed. Our objective in 1986 was to determine whether egg sampling vs. conventional treatment criteria (e.g., larval infestations, trap catches of male moths, and /or fixed -spray intervals) provided more optimal timing of insecticide applications in a 640-ac field test. Implementation of the egg sampling method in 8 of the 16 fields resulted in an average 35 percent seasonal reduction in insecticide use when compared to conventional methods. Despite the reduction in insecticide use, PBW larval infestations were not significantly different (P = 0.45) in fields samples for eggs vs. fields sampled for larvae from June to September. Yields were also not significantly different (P = 0.40) between the two sets of fields.