Three annual applications of glyphosate [N-(phosphonomethyl)glycine] with three ropewick applicators were compared to hoeing and cultivation for the control of johnsongrass [Sorghum halepense (L.) Pers. ♯3 SORHA] in cotton (Gossypium hirsutum L. ‘Acala SJ-2′) in 1980 and 1981. The three applicators provided about equal control of johnsongrass. Averaged over treatments, years, and dates of application, plots treated with glyphosate contained 83% fewer live johnsongrass shoots (14/m2) than cultivated control plots (84/m2) 2 to 3 weeks after each application. Glyphosate-treated plots yielded an average of 81% more seed cotton (2010 kg/ha) than cultivated control plots (1110 kg/ha). However, yields of treated plots averaged 33% less than plots maintained weed-free by hoeing. Although applications of glyphosate reduced johnsongrass populations 83%, the competitive effect of johnsongrass on cotton prior to the initiation of treatments, plus the competition from escape plants between treatments, prevented cotton from yielding normally.

Ivyleaf morningglory [Ipomoea hederacea (L.) Jacq. # IPOHE], planted in 1984 and 1985 the first of each month from April through August, began emerging in cotton (Gossypium hirsutum L. ‘Acala SJ-2’) 1 week after planting. Morningglory, at a density of 1 plant/2 m of row, emerging in April and May became so competitive to cotton by harvest in September that the total crop was lost. June plantings, although less competitive than earlier plantings, still reduced yields by 11%. Later plantings did not reduce yields of cotton. Morningglory plantings that produced seed (April through July) began flowering within 7 weeks, and viable seed was collected for the first time 9 weeks after planting. Ivyleaf morningglory plants that emerged in April and May produced about 11 000 seed/plant by cotton harvest. This compared to 3000 and 93 seed/plant for morningglory that emerged in June and July, respectively. The earliest that morningglory might be expected to produce seed in cotton planted in early April would be late May to early June, and morningglory emerging as late as the first of July could produce some seed by cotton harvest.

Several herbicide-based weed management programs for glyphosate-tolerant cotton were compared in eight field studies across Alabama during 1996 and 1997. Weed management programs ranged from traditional, soil-applied residual herbicide programs to more recently developed total postemergence (POST) herbicide programs. Pitted morningglory and sicklepod control was best achieved with fluometuron applied preemergence (PRE) followed by (fb) a single POST over-the-top (POT) application of glyphosate fb a POST-directed application of glyphosate. Annual grass control was better with the preplant incorporated (PPI) programs at two of three locations in both years. Treatments that included at least one glyphosate POT application gave increased grass control over no glyphosate or pyrithiobac POT. Velvetleaf control was improved with the addition of glyphosate POT. A herbicide program using no POST herbicides yielded significantly less seed cotton than any program using POST herbicides at one location. PRE- and POST-only weed management programs at another location produced more seed cotton and gave greater net returns than PPI programs. Similarly, net returns at that same location were equivalent for both PRE- and POST-only programs, and less for PPI programs. POST-only programs yielded highest amounts of seed cotton and netted greater returns.