Yellow nutsedge infests a large number of hectares in the Treasure Valley of eastern Oregon and western Idaho. Much of its continued expansion appears to be related to onion production in the valley. Fall applications of metham often produce inconsistent results when used to control yellow nutsedge before planting an onion crop. Trials were conducted in the laboratory to determine the influence on yellow nutsedge control of metham dose, duration of exposure, temperature during exposure, and tuber conditioning by washing and chilling at 3 C. All factors influenced metham efficacy against yellow nutsedge tubers. The dose causing 50% reduction in sprouting tubers (I 50) for metham ranged from 22 to 76 mg kg−1 of soil and was lower for conditioned tubers than nonconditioned tubers across all conditions, except when tubers were exposed at 25 C for 3 d. Nonconditioned tubers were unaffected by metham after 1 d exposure at 5 C. Increasing exposure temperature or increasing exposure duration decreased sprouting for nonconditioned tubers. As exposure duration and exposure temperature increased, differences among conditioned and nonconditioned tubers were less. Temperature and exposure duration affects metham efficacy against yellow nutsedge, and the condition of the tubers at the time of treatment also has a significant effect. Applications of metham at a time when yellow nutsedge tubers are not dormant may improve yellow nutsedge control.

Metham has been reported as an acceptable weed control alternative to methyl bromide. However, modified application equipment is required to allow its effective use in crops that are grown on polyethylene-covered seedbeds. A power tiller was modified using commonly available materials to apply metham in a 61-cm band and shape seedbeds for laying a black polyethylene tarp. Additional modification allowed the implement to be used in strip tillage and conventional tillage systems. Metham applied using this modified power tiller effectively controlled many species of weeds, including yellow nutsedge, in transplanted watermelon.

Field trials were conducted to determine the effect of fumigant-pebulate combinations on purple nutsedge density in fresh market tomato. Treatments consisted of methyl bromide plus chloropicrin (MBr plus Pic) [67:33] at rates of 270 and 130 kg/ha, respectively; Pic plus pebulate at 400 and 4.5 kg/ha, respectively; metham (MNa) plus pebulate at 485 and 4.5 kg/ha, respectively; dazomet plus pebulate at 950 and 4.5 kg/ha, respectively; and 1,3-dicholopropene plus Pic (C-17) [87:13] plus pebulate at 392 and 4.5 kg/ha, respectively. At 12 wk after treatment, MBr plus Pic controlled purple nutsedge more effectively (10 plants/m2) than the fumigant-pebulate combinations (50 to 70 plants/m2). Compared to MBr plus Pic, Pic plus pebulate had a 14% lower marketable yield. No differences in marketable yield were noted with dazomet plus pebulate or C-17 plus pebulate compared to MBr plus Pic. However, MNa plus pebulate produced a 15% higher yield than MBr plus Pic. Additionally, MNa plus pebulate had 15% higher marketable fruit weight than MBr plus Pic.

Field trials were conducted to compare the effect of various soil fumigants along with in-bed pebulate and row-middle metribuzin applications on purple nutsedge control and on tomato and bell pepper growth and yield. Treatments consisted of combinations of soil fumigants, pebulate, and metribuzin. Fumigants levels were (1) untreated control, (2) methyl bromide (MBr) + chloropicrin (Pic) (67 + 33%, respectively), (3) Pic, (4) metham, (5) dazomet, and (6) 1,3-dichloropropene (1,3-D) + Pic (83 + 17%, respectively). Pebulate levels were either applied in-bed or not applied. Row middles were either sprayed with metribuzin or untreated. In both crops, purple nutsedge populations were independently influenced by fumigants and pebulate applications, with the highest number of purple nutsedge plants in the untreated control. The addition of pebulate reduced purple nutsedge populations in all treatments. In tomato trials, the yield was affected by fumigants, with the highest losses (53 and 50% reductions in fruit number and weight) observed in the nonfumigated control. In pepper trials, fruit number and weight were individually influenced by fumigants and metribuzin sprayings. Application of metribuzin to row middles increased yields 10% relative to nontreated plots.

Studies were conducted from 1998 to 2001 in Tifton, GA, on weed management systems in transplanted cantaloupe and watermelon grown on polyethylene-covered seedbeds. Soil fumigants were metham (748 L/ha) and a nonfumigated control. All metham applications were sprayed in a 61-cm band and incorporated with a modified power tiller. Herbicide treatments were ethalfluralin (0.8 kg ai/ha) premergence (PRE), ethalfluralin plus halosulfuron (36 g ai/ha) PRE, ethalfluralin PRE followed by glyphosate (1.1 kg ai/ha) postemergence POST-SHIELDED, ethalfluralin plus halosulfuron PRE followed by glyphosate POST-SHIELDED, and a nontreated control. Premergence herbicides were directed to row middles not covered in polyethylene, without contacting the transplants. Glyphosate was applied to row middles using a hooded sprayer, just before vine running. Overall weed control was not improved with soil fumigation in either cantaloupe or watermelon, and there was no yield response in either crop. There may be minimal benefit in transplanted cantaloupe and watermelon on polyethylene-covered seedbeds from preplant soil fumigation for weed control, in the absence of other pests. Herbicide systems that included halosulfuron PRE or glyphosate applied POST-SHIELDED improved control of yellow nutsedge compared with ethalfluralin alone. Control of Texas panicum, southern crabgrass, Florida pusley, and smooth pigweed was not improved by halosulfuron or glyphosate. Polyethylene-covered seedbeds provide a mechanical barrier to weed infestation for many species. Integration of these weed control practices gives cantaloupe and watermelon growers effective options for weed management, particularly for a troublesome species such as yellow nutsedge.