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Harvest-aid chemicals are used on more than three-quarters of the cotton acreage in the United States. They are considered to be a necessity if cotton is stripper-harvested before frost and to be advantageous if high-quality fibre is spindle-picked from rank, heavily fruited plants with a lot of green leaf. Economic benefits do not always follow their use, however; the degree of success depends largely on relationships between chemicals, techniques, plant conditions and climate.

Greenhouse and field studies were conducted to evaluate the effects of multiple applications of chlordimeform on the growth and development of cotton, Gossypium hirsutum. L., plants, and on early season insect populations. Plants were sprayed six times with chlordimeform either alone or in combination with fenvalerate at 5- to 7-d intervals, beginning at the six-leaf stage of plant development. In the absence of early season insects and when insect populations were maintained at a relatively low level, no increases in lint yield occurred on the chlordimeform-treated plants. However, yield increases did occur and insect populations became lower in these treated plots when early season insect populations in the test area were relatively high. None of the treatments influenced the boll components boll Size, seed index, lint index, and lint percentage, or the fiber properties length, strength, and micronaire.

The effects of foliar application of potassium 3,4-dichloroisothiazole-5-carboxylate (TD-1123) and S,S,S-tributyl phosphorotrithioate (DEF) on some physiological events that occur in cotton (Gossypium hirsutum L.) leaves are reported. Transport of 14C from cotton leaves was significantly reduced as soon as 1 day after treatment with DEF. In addition the DEF-treated leaves exhibited reductions in water potential recovery values (predawn measurements), stomatal conductance, specific weights, soluble N content, and an alteration in free amino acid distribution. Little change in any of these parameters was noted in leaves treated with TD-1123 alone. A sequential treatment of TD-1123 followed in 10 days with DEF had an apparent synergistic effect in that the effect on most parameters measured was more pronounced and occurred earlier in such leaves than in those treated with either chemical alone.

The phosphate defoliant DEF (S,S,S-Tributylphosphorothrithioate) was sprayed on presquaring greenhousegrown cotton (Gossypium hirsutum L.) plants. Plant water status and leaf area data were taken at 3-hour intervals during the 1st day and daily thereafter. Stomatal diffusion resistance was measured during the 1st day only. Leaves were analyzed for total N, soluble N, and distribution of free amino acids. Little change in any of the parameters measured was noted the 1st day. On subsequent days the DEF-treated leaves had lower leaf water potential recovery values (predawn measurement) and lower specific weights (fresh weight basis). DEFtreated leaves, however, had a higher specific leaf weight on a dry weight basis. Leaf N percent did not change as a result of the DEF treatment. Soluble N increased up to twice that of the controls by the 3rd day. The distribution of free amino acids in DEF treated leaves was altered. The concentrations of all amino acids except aspartic acid, glutamic acid + glutamine, proline and valine were significantly increased in the DEF treated leaves. The exceptions remained stable or tended to decrease. The results indicated that DEF-treated leaves may be mobilizing the leaf protein prior to abscission, but that transport out of the leaf is impeded. Further experiments are needed to substantiate this notion.

Greenhouse and laboratory studies were conducted to determine if chlordimeform affected percent egg hatch of Lygus lineolaris (Palisot de Beauvois). Pole bean ( Phaseolus vulgaris L.) pods and cotton ( Gossypium hirsutum L.) plants in which L. lineolaris adults had deposited eggs were treated with chlordimeform; nymphs were counted 7 days after adults were removed. When pole bean pods were sprayed with or immersed in a 0.09% solution of chlordimeform, nymphal emergence was not significantly reduced. When cotton was sprayed with chlordimeform, emergence of nymphs was significantly reduced in two of three tests.