Evaluation of Isothiocyanates and Herbicide Programs as Methyl Bromide Alternatives for Weed Control in Polyethylene-Mulched Tomato and Bell Pepper

Methyl bromide (MeBr), a Class I ozone –depleting substance, has been banned for ordinary agricultural uses. In the absence of an effective MeBr alternative, weed control is a major challenge for commercial tomato and bell pepper production. Field trials were conducted at Fayetteville, AR, to compare allyl isothiocyanate (ITC), metam sodium, and herbicide programs with the standard MeBr application (mixture of MeBr plus chloropicrin at 67% plus 33%, respectively, hereafter referred to as MeBr) for crop injury, weed control, viable yellow nutsedge tubers, and marketable yield in low–density polyethylene (LDPE) mulched tomato and bell pepper production. In addition, herbicide programs were evaluated for cost of production, gross return, net return, and net return relative to MeBr in LDPE–mulched tomato and bell pepper production. Allyl ITC and metam sodium did not injure tomato. Weed control and yield in tomato plots treated with allyl ITC at 750 kg ha -1 or metam sodium at 360 kg ha-1 were comparable to plots treated with MeBr at 390 kg ha-1. Likewise, metam sodium at 360 kg ha-1 and MeBr–treated bell pepper plots were similar for weed control and yield. Tomato or bell pepper injury was ≥13% in PRE-applied imazosulfuron or S–metolachlor plots after POST-applied trifloxysulfuron plus halosulfuron at 0.008 and 0.027 kg ha-1, respectively. Herbicide programs consisting of PRE–applied S–metolachlor followed by (fb) POST–applied trifloxysulfuron plus halosulfuron provided comparable weed control to MeBr in LDPE–mulched tomato and bell pepper. Tomato or bell pepper plots treated with the S–metolachlor–containing herbicide program yielded total marketable fruits equivalent to the plots treated with MeBr. The S–metolachlor herbicide program also provided a net return of 3,758.50 and 9,912.05 dollars ha-1 in tomato and bell pepper production, respectively. Moreover, the S–metolachlor herbicide program added a net return of $173.34 ha-1 relative to net return with MeBr treatment in bell pepper. In conclusion, metam sodium at 360 kg ha-1 or PRE-applied S–metolachlor at 1.6 kg ha-1 fb POST–applied trifloxysulfuron plus halosulfuron at 0.008 and 0.027 kg ha-1 are viable MeBr alternatives for weed control in LDPE–mulched tomato and bell pepper.