EFFECT OF HERBICIDES ON IVYLEAF MORNINGGLORY (IPOMOEA-HEDERACEA) INTERFERENCE IN SOYBEAN (GLYCINE-MAX)

Ivyleaf morningglory weed-free period, weedy period, and density studi es were conducted in 1993 and 1994 to determine the effects of soil-ap plied imazaquin and chlorimuron plus metribuzin on ivyleaf morningglor y interference in soybean. A weed-free period of 4 wk was needed to ma intain soybean yield equivalent to weed-free season long when herbicid es were not used, but treatment with either chlorimuron plus metribuzi n or imazaquin maintained yield comparable to weed-free at all interva ls. Ivyleaf morningglory biomass was reduced by both herbicides across all weed-free periods. The period nontreated ivyleaf morningglory pla nts were tolerated without yield loss was only 2 wk, but this interval was extended to 8 wk after treatment with chlorimuron plus metribuzin or imazaquin. Without herbicides, soybean yield was reduced by four i vyleaf morningglory per m of row but the highest population evaluated in this study (eight per m of row) did not reduce soybean yield after treatment with chlorimuron plus metribuzin or imazaquin. Ivyleaf morni ngglory biomass was reduced at all densities after treatment with eith er herbicide.