Morningglory species are among the most troublesome weeds in cotton. Their presence at harvest often results in lint staining and increased leaf trash, thereby causing dramatic reductions in cotton quality. Nine treatments, including an untreated check and weedfree check, defoliants and herbicide/defoliant combinations were evaluated for their efficacy on defoliation and desiccation of pitted morningglory (PMG), Ipomoea lacunosa L., in cotton. Additionally, the effects of PMG on fiber properties and lint quality were quantified.

The experiment was established at the Pee Dee Research and Education Center, Florence, S.C., on a Goldsboro loamy sand in 1988 and at an on-farm site in Calhoun County, S.C. on a Greenville sandy loam in 1990. A naturally occurring PMG infestation existed at these sites. Plots were four rows wide in 1988 and two rows wide in 1990, 30 ft long, and were arranged in a randomized complete block design with four replications in 1988 and three replications in 1990. The row spacing was 38 inches. Treatments were applied Sept. 14, 1988 and Sept. 19, 1990. Visual ratings of percent PMG defoliation and desiccation were recorded two weeks later. The aboveground portion of PMG plants was harvested from two square meters from the center of each plot. Leaves and vines were separated and fresh weights were recorded. Dry weights were recorded after drying for two weeks at 150 F. The two center rows of each plot were harvested with a spindle picker, and a portion of the harvested cotton was ginned on a laboratory gin to obtain lint for quality determinations.

In 1988, Roundup(RU)+Folex(F)+Surfactant(S) @ 32+16+14 oz/ac and RU+Harvade(HAR)+S @ 32+8+14 oz/ac were more effective in defoliating PMG (83 and 98%, respectively) than the other harvest aids evaluated [F @ 24 oz/ac (O%), HAR+Crop Oil Concentrate(COC) @ 8+16 oz/ac (50%), Gramoxone Super(GS)+F+S @ 11+12+14 oz/ac (40%), GS+HAR+S @ 11+8+14 oz/ac (56%), GS+Prep(P)+S @ 11+21+14 (51%)], and the untreated check (O%) and the weed-free check [defoliated with F+Dropp(D)+P @ 16 oz+o.l lb+21 oz/ac].

In 1990, no treatment provided satisfactory defoliation of cotton. A cool, wet period following treatment application may have contributed to poor defoliation. Leaf desiccation was highest for HAR+GS and P+GS treatments with 11 and 10%, respectively. Boll desiccation ranged from 19 to 25% for the three treatments containing GS and for the F+D+P treatment.

Satisfactory desiccation of PMG vines in 1988 was not provided by any treatment evaluated. RU+HAR+S had a visual rating of 85%, which was almost twice the rating of any other treatment. However, ratios of vine fresh wt/dry wt indicated no desiccation of vines with any treatment except RU+F+S. Vine desiccation with RU+F+S may be due to greater translocation of RU by PMG leaves when F was used and no defoliation occurred.

PMG defoliation and vine desiccation responses in 1990 were similar to those obtained in 1988. RU+HAR+S and F+RU+S defoliated 98 and 85% of the PMG leaves, respectively. However, vine desiccation was not as great as that obtained in 1988. F had no activity on defoliation or vine desiccation of PMG.

Slight variations in fiber properties were observed each year, but differences were attributed to variations in weed populations rather than treatments. Trash content as measured by high volume instrumentation (HVI) was similar in the weed-free check (F+D+P) and where cotton was treated with RU+HAR+S, reflecting the excellent (98%) defoliation of PMG in 1988. The trash content for other treatments was greater than that observed in weed-free cotton. Fiber color as measured by HVI indicated no difference between the weed-free check (F+D+P) and RU+HAR+S. However, the reflectance of the weed-free cotton was significantly higher than the other treatments. These differences were not evident in 1990. Poor cotton defoliation may have been a factor contributing to these results.

RU+HAR+S appeared to offer potential for defoliating and providing some vine desiccation of PMG after evaluation in 1988. However, results in 1990 indicate harvest aids are not a satisfactory means of limiting quality reductions of cotton fiber caused by PMG.

Slight variations in variations in weed populations rather than treatments. Trash content as measured by high volume instrumentation (HVI) was similar in the weed-free check (F+D+P) and where cotton was treated with RU+HAR+S reflecting the excellent (98%) defoliation of PMG in 1988. The trash content for other treatments was greater than that observed in weed-free cotton. Fiber color as measured by HVI indicated no difference between the weed-free check (F+D+P) and RU+HAR+S. However, the reflectance of the weed-free cotton was significantly higher than the other treatments. These differences were not evident in 1990. Poor cotton defoliation may have been a factor contributing to these results.

RU+HAR+S appeared to offer potential for defoliating and providing some vine desiccation of PMG after evaluation in 1988. However, results in 1990 indicated harvest aids are not a satisfactory means of limiting quality reduction of cotton fiber caused by PMG.