Search

A cultural system for short-season cotton, Gossypium spp., incorporating narrow rows (two rows ca. 36 cm apart on beds spaced ca. 102 cm apart) and early irrigation cutoff resulted in early-maturing cotton in Imperial Valley, Calif., with harvests completed by 24 August 1978. Yields were over 4,000 kg of seed cotton per ha with no insecticide applied for insect control. Cotton yields in systems with full-season, conventional-row (one row on a bed, 102 cm between rows) cultivation without insecticide treatments but with five additional irrigations were significantly lower than those in the short-season system in August and after full-season production on 15 November 1978. The early maturation of the crop in the short-season system avoided infestations of late-season, Pectinophora gossypiella (Saunders), reduced larval population in the bolls, trash, and soil (75%) in the fall, and reduced spring emergence of moths from overwintered larvae (81%) relative to the same parameters from the conventional full-season cotton crop. Cotton yields in full-season narrow-row and conventional-row systems were significantly higher when the top crop was protected from pink bollworm losses with insecticides. Cotton yields of several short-season and full-season cotton varieties and cultivars, grown under the narrow-row, short-season system, were not significantly different. Thus, currently available commercial cultivars and short-season variety genotypes are adaptable to short-season cotton growing conditions in the Southwest.

Applications of plant growth regulators in late August effectively terminated the fruiting of cotton and significantly reduced populations of diapausing larvae of Pectinophora gossypiella (Saunders) (by 90% or more) in Arizona during 1972–74. As a result, fewer overwintered moths (39%) emerged the following spring from terminated plots. Applications in mid-, or late August were more effective than applications in early September. Yields were not significantly reduced by most treatments. The most effective materials tested were 2.4-D (amine salt of 2,4-dichlorophelloxy) acetic acid + chlorflurenol (methyl 2-chloro-9-hydroxyfluorene-9-carboxylate) and 2, 4-D + chlormequat ((2-chloroethyl) trimethylammonium chloride).

Improving cotton (Gossypium spp.) heat tolerance (ability to set bolls in high temperature environments) has been an important aspect of the American Pima (Pima) cotton (G. barbadense L.) breeding program for over 25 years. However, heat tolerance is difficult to quantify. This report estimates change in heat tolerance of Pima cotton through yield response over 30 years in six Arizona counties that differ in elevation and mean summer temperatures. Pima cotton/upland cotton (G. hirsutum L.) lint yield percentages were compared for each county by regression with year of production. County mean yield percentages were also compared with elevations. Pima cotton yields as percentages of upland cotton yields increased in five of the six counties over the 30-year period. Pima lint yield increased from 57 % of upland yield in 1956 to 75 % in 1985 when averaged over the six counties. This increase represents an estimated 206 kg lint ha-1 in addition to any upland yield increase. Comparison of regression coefficients suggest that nearly 50 % of the 30-year lint yield increase of Pima cotton at lower elevations was the result of increased tolerance to high temperature in improved cultivars. County 30-year mean Pima cotton lint yields as percentage of upland cotton yield increased significantly (P < 0.001) from 52.2% to 82.1 % as county elevations increased from 37 m to 1273 m (cooler summer temperatures). These results support reports of greater heat tolerance for upland cotton than Pima cotton, but also show that the difference between species has been reduced substantially by breeding in the last 30 years.

The numbers of diapausing larvae of Pectinophora gossypiella (Saunders) found in soil and trash in the fall after harvest in cotton were reduced by early irrigation cut-off and chemical termination treatments. Also, the number of moths that emerged the following spring was reduced by the combination of the 2 treatments. The early irrigation termination reduced pink bollworm infestations in bolls and Heliothis spp. oviposition in the fall, but there was no effect due to the chemical termination.

The effects of the numbers of pink bollworm (PBW), Pectinophora gossypiella (Saunders), per boll of Deltapine 16, a cultivar of upland cotton, Gossypium hirsutum L., and Pima S-5, a cultivar of American Pima cotton, G. barbadense L., were evaluated. For each PBW per boll, lint losses were 14 and 24%, and seed weight losses were 12 and 22%, in Deltapine and Pima, respectively. The relationship between PBW per gram seed-cotton and boll dry weight was the same in both cultivars, which indicated that the infestation susceptibility was the same in both cultivars. However, in the smaller bolls with equal larval densities, the percentages of damaged seed were greater in Pima than in Deltapine. In both cultivars, the lint per seed was negatively correlated to the percentage of damaged seed. The percentage of fluorescent seed (an index of aflatoxin-forming fungus) increased with the number of larvae per boll. Lint quality decreased as the infestation level increased.

Fewer Bucculatrix thurberiella Busck were present and less leaf damage was done in plantings of nectariless cotton, Gossypium hirsutum L., than in plantings of nectaried cotton. Also, numbers of Lygus spp. were reduced, as well as total predator populations. Consistently fewer Chrysopa spp. and Geocoris spp. were present.

Substantial mid- and late-season topping of American Pima cotton (Gossypium barbadense L.) plants occurs in field plantings. Lygus bug (Lygus hesperus Knight) feeding is the apparent cause of topping. The effects of mid to late.season topping on lint yield and several yield components of ‘Pima S-4’ cotton were examined. Topping of Pima S-4 cotton in mid-July, early.August, and mid-August reduced plant height, reduced the number of main stem nodes, increased boll set on top fruiting branches, and resulted in additional branch nodes on top fruiting branches. Plants topped 17 July produced 300%, 100%, and 60% more bolls on the first, second, and third branch, respectively, below the point of topping than did the check plants. The effect was less when topping was later in the season. The yield patterns in lower branches were not different from the checks. Topping did not affect: 1) lint yield (3 years), 2) number of bolls set, seed/boll, 4) lint/boll, 5) lint/seed, 6) seed weight, days to boll maturity, or 8) pink bollworm infestation. Fruit set was not delayed by topping. Fruiting points, which aborted on normal plants, produced bolls on topped plants up to the potential for the cultivar and environment. This has important implications for studies on insect damage to plants and for efforts to increase lint yield by reducing boll abscission.