Three herbicide treatments were evaluated for use under clear polyethylene mulch and three types of row covers (spunbonded polyester, double-slitted polyethylene, and perforated polyethylene). Treatments included combinations of bensulide {O,O-bis(1-methylethyl)-S-[2-[(phenylsulfonyl)amino]ethyl]phosphorodithioate} and naptalam {2-[(1-naphthalenylamino)carbonyl]benzoic acid}, and cinmethylin {exo-1-methyl-4-(1-methylethyl)-2-[(2-methylphenyl)methoxy]-7-oxabicyclo [2.2.1] heptane} alone and in combination with naptalam. In 1985 and 1986, all herbicide treatments controlled more than 95% of carpetweed (Mollugo verticillata L. # MOLVE) and large crabgrass [Digitaria sanguinalis (L.) Scop. # DIGSA], except for the combination of bensulide plus naptalam in 1986, which controlled only 73 to 85% of these weeds. In both years, all herbicide treatments reduced crop vigor at 3 weeks but not at 7 weeks after transplanting. Total yield was not different with any of the herbicide treatments in 1985 and 1986. However, in 1986, yields were greater from the bensulide plus naptalam treatment than for the weed-free control. Herbicide treatment did not affect early yields in 1985, but the bensulide plus naptalam treatment was greater than all others in 1986. The use of row covers did not increase herbicide-induced crop injury over that of clear mulch alone. Greenhouse studies indicated that soil-applied cinmethylin reduced muskmelon root and shoot weight. Foliar applications reduced muskmelon shoot weight.

Purple and yellow nutsedge are the most troublesome weeds of vegetable crops in the southeast United States. Elimination of methyl bromide use will require alternative management programs to suppress nutsedge growth and interference in vegetables. Polyethylene mulch is an effective barrier for most weeds; however, nutsedges can proliferate in beds covered with polyethylene mulch. The influence of polyethylene mulch on shoot production and lateral expansion patterns of single tubers of purple nutsedge and yellow nutsedge over time was evaluated in field studies. Purple nutsedge patch size was similar in the black mulch treatment and nonmulched control after 8 and 16 wk after planting (WAP). By the end of the growing season, purple nutsedge patch size in the black mulch treatment was nearly twice that in the nonmulched control. At 32 WAP, there were 1,550 shoots in the 16.1 m2 patch in the black mulch treatment and 790 shoots in the 8.1 m2 patch in the nonmulched control. In contrast, yellow nutsedge growth was suppressed in the black mulch treatment, relative to the nonmulched control. Compared with the black mulch treatment at 16 and 24 WAP, the nonmulched control produced nearly three times as many yellow nutsedge shoots (140 shoots at 16 WAP and 210 shoots at 24 WAP) and patches that were twice the size (0.10 m2 at 16 WAP and 0.18 m2 at 24 WAP). These data indicate that there are significant differences in the growth habits of the two nutsedges species in mulched vegetable systems. The differences in response to black mulch will likely lead to purple nutsedge becoming a greater problem, relative to yellow nutsedge, in vegetable systems. The rapid expansion of a single purple nutsedge shoot to form a patch that is 22.1 m2 and containing 3,440 shoots at 60 WAP illustrates the importance of managing this species.