A 16-YR SURVEY ON LEVELS OF JOHNSONGRASS (SORGHUM-HALEPENSE) IN ARKANSAS, LOUISIANA, AND MISSISSIPPI

A survey was conducted in Mississippi from 1976 and in Arkansas and Lo uisiana from 1977 through 1991 to determine annual variation of johnso ngrass infestation in cotton and soybean fields. The survey route was 1534 km long. Levels ofjohnsongrass infestation were estimated in 752 +/- 296 cotton fields and 884 +/- 407 soybean fields in each year of t he survey. The area of fields surveyed annually was 47 000 +/- 21 000 ha of cotton and 52 000 +/- 19 000 ha of soybeans. Johnsongrass was pr esent in 55 to 90% of the cotton fields. The percent of cotton fields with johnsongrass was about the same in 1991 as in 1976-77. About 90% of the soybean fields in Mississippi and Louisiana had johnsongrass, b ut only 70 to 80% of soybeans fields in Arkansas had johnsongrass. Soy bean fields with 1 to 5% levels of infestation increased slightly in M ississippi but remained about the same in Arkansas and Louisiana. Soyb ean fields with infestations of 6% or more slightly decreased in Arkan sas and Louisiana but not in Mississippi. It was estimated that johnso ngrass reduces the average annual value of harvested cotton $5.8 +/- 1 .9 million and soybeans $23.7 +/- 0.6 million in the three states.