Cotton fields were surveyed in late season, either immediately before or after harvest. A total of 74 fields were surveyed (54 in central and western counties and 20 in eastern counties). This survey sampled 5600 acres of cotton. The total acreage of cotton planted in Arizona in 1989 was approximately 485,000 acres. The weed numbers shown below represent mature weeds only. These weeds were not controlled by herbicides, cultivation, or hand weeding. The survey technique consisted of counting all mature weed on two adjacent rows (76 to 80 inches wide) for 50 feet, or a total of 100 row feet. Four areas were randomly sampled in each field for a total of 400 row feet in each field. Fields were also randomly selected across the sample area. Adjacent fields were avoided.

A total of 17 weed species were identified. Nutsedge represented the most serious weed problem in Arizona. Purple and yellow nutsedge were present in 65% of the western counties and yellow nutsedge was present in 45% of the eastern counties. Some infestations of nutsedge reduced cotton stands. Johnsongrass and field bindweed were also serious weed problems in the eastern counties. Annual morningglory was the most widespread annual broadleaf weed throughout the state. Red sprangletop, a late season annual grass, was the most prevalent annual grass at harvest time.

This survey gives further evidence of the increasing importance of perennial weeds in Arizona cotton fields. Purple and yellow nutsedge were present in over 50% of the acreage surveyed. The density of the nutsedge infestation was more severe in the central and western counties. About 40% of the fields infested with nutsedge had populations exceeding 1 stem/ft² and some contained infestations of over 20 stems/ft². Only 10% of the nutsedge infestation in eastern Arizona exceeded 1 stem/ft². There is every reason to believe that this infestation level will continue to increase in the central and western counties.

Bermudagrass and johnsongrass were not controlled in some fields especially in the eastern counties. There are effective control measures available such as Poast and Fusilade 2000, but these weeds remain as a problem to some growers. Field bindweed is a very serious problem in Graham county.

Annual morningglory was the most widespread annual broadleaf weed in all areas. Very few fields were completely covered with this vine; however, an average of 2 plants/100 row feet in the eastern counties indicates that it is a very serious problem. Control programs do exist for this weed problem, but require timely application of herbicides, cultivation, and some hand weeding. Unless growers are willing to follow a careful, full-season program, from preplant to layby, annual morningglory will continue to be a problem.

Red sprangletop is a late season annual grass that has become widespread throughout the cotton growing area. It appears to be a serious problem only in thin or partial cotton stands and, perhaps, after the preplant "yellow herbicide" has begun to breakdown in the soil.

My general impression was that, except for perennials, most growers are achieving acceptable control of weeds in cotton.