Comparing Fumigant Retention of Polyethylene Mulches for Nutsedge Control in Florida Spodosols

Although methyl bromide (MBr) has been phased out in developed countries, limited amounts will still be available in the United States for the next few years through critical-use exemptions. Therefore, production practices reducing MBr use are desirable from the grower and environmental standpoints. Fumigation efficacy depends on the duration of fumigants in the soil and mulch permeability; thus, field trials were conducted to compare MBr retention of low- and high-density polyethylene (LDPE and HDPE respectively) mulches with seven metallized mulches and virtually impermeable films (VIF) from different manufacturers, and to assess the effect of MBr retention on nutsedge ( Cyperus rotundus and C. esculentus ) control with these mulches. The compared mulches were 1) white VIF; 2) black VIF; 3) white-on-black VIF; 4) cowound VIF, which has a clear nylon layer that covers the bed and is superimposed with a layer of black HDPE mulch; 5) metallized; 6) metallized heat trap with a black stripe on the bed center; 7) metallized with a black stripe on the bed center; 8) black LDPE mulch; and 9) black HDPE mulch. All treatments received 175 lb/acre of MBr + chloropicrin (Pic; 67:33 v/v). A nonfumigated control plot covered with LDPE mulch, and a treatment covered with HDPE mulch and fumigated with 350 lb/acre of MBr + Pic were also established. Nutsedge emergence through mulches increased rapidly beginning 18 days after treatment (DAT). Nutsedge populations at 28 DAT in the nonfumigated control covered with LDPE mulch had the greatest emergence (88.8 plants/ft 2 ), followed by LDPE and HDPE mulches with 175 lb/acre of MBr + Pic (67.0 plants/ft 2 ), HDPE mulch with 350 lb/acre of MBr + Pic (25.0 plants/ft 2 ), and VIF and metallized mulches with 175 lb/acre of MBr + Pic (<2 plants/ft 2 ). There were no significant differences in fumigant retention between the metallized mulches and VIF. These mulches retained 3.7 and 1.8 times more MBr than HDPE and LDPE mulches fumigated with 175 and 350 lb/acre of MBr + Pic, respectively.