POTENTIAL OF COMBINATION TREATMENTS OF METHYL DISULFIDE AND METAM SODIUM FOR WEED CONTROL R. Rodriguez-Kabana and Lee Simmons Department of Entomology and Plant Pathology Auburn University & Alabama Agricultural Experiment Station Auburn, Alabama 36849, U.S.A. rrodrigu@acesag.auburn.edu The herbicidal properties of combinations of methyl disulfide [(CH 3 ) 2 S 2 ; MDS] and metam- sodium [MS] were studied in greenhouse experiments with a sandy loam soil [pH 6.5; org. matter <1%; C.E.C.< 10 meq./100 gms soil] from a cotton field. The soil was infested with a variety of weed species principal among which were: crabgrass [ Digitaria sanguinalis ] and other gramineae, pigweed [ Amaranthus spp.], morning glories [ Ipomea spp.], sicklepod [ Cassia tora ], and yellow nutsedge [ Cyperus esculentus ]. MDS and MS were delivered as a drench in water equivalent to 1" acre. MS was applied using the Vapam HL R formulation at rates of: 6.4, 13.1, 26.2, and 39.2 mgs a.i./Kg soil. These rates were applied with MS alone and in combination with MDS [Aldrich, Milwaukee, WI, U.S.A.] at 750 mgs a.i./Kg soil. MDS was also applied alone at rates of 250, 500, 750, and 1000 mgs a.i./Kg soil. The experiment included no treatment controls. Each treatment was represented by 7 replications [pots] in a randomized complete block design. Each pot contained 1 kg soil. The pots with soil were covered with transparent polyethylene bags [1 mil] immediately after treatment. The bags were removed after10 days and the number of weeds were counted at 10, 18, 25, and 39 days after application of the chemicals. . Combination treatments resulted in superior control of all weed species compared with or MS alone as shown in Fig. 1 for yellow nutsedge. Applications of MDS were ineffective against yellow nutsedge and crabgrass [Fig. 2] but resulted in satisfactory control of pigweed and other broad leaf weeds when applied at rates > 500 mgs [Fig. 3]. Results suggest strong synergy for herbicidal activities between the two compounds. The data support the possibility of combining MDS and MS for development of alternatives to methyl bromide for soil fumigation 14-1
8 10 YELLOW NUTSEDGE 7 YELLOW NUTSEDGE � � CYPERUS ESCULENTUS � � � CYPERUS ESCULENTUS 8 6 � � WEEDS PER POT NO MDS � T NO MDS 5 � O WITH MDS � P WITH MDS 6 R E 4 P S 10-DAY COUNT D 18-DAY COUNT � E 4 3 E W FLSD[p0.05] = 2.38 FLSD[p0.05] = 2.60 � 2 � 2 1 � � � � � � � � � � � 0 0 MDS MDS 0 6.5 13 19.5 26 32.5 39 0 6.5 13 19.5 26 32.5 39 (750 MGS/KG) (750 MGS/KG) METAM SODIUM RATE [MGS/KG SOIL] METAM SODIUM RATE [MGS/KG SOIL] 10 10 � � YELLOW NUTSEDGE YELLOW NUTSEDGE � � � CYPERUS ESCULENTUS CYPERUS ESCULENTUS 8 8 � � � WEEDS PER POT NO MDS WEEDS PER POT NO MDS � � WITH MDS � WITH MDS 6 6 � 25-DAY COUNT 39-DAY COUNT 4 4 � � FLSD[p0.05] = 2.50 FLSD[p0.05] = 2.42 � 2 2 � � � � � � � � � 0 0 MDS MDS 0 6.5 13 19.5 26 32.5 39 0 6.5 13 19.5 26 32.5 39 (750 MGS/KG) (750 MGS/KG) METAM SODIUM RATE [MGS/KG SOIL] METAM SODIUM RATE [MGS/KG SOIL] Figure 1. Effect of metam Na [Vapam HL R ] applied by drenching alone and in combination with methyl disulfide [MDS]on the incidence of yellow nutsedge [ Cyperus esculentus ] in a greenhouse experiment 10, 18, 25, and 39 days after delivery into soil in 1" acre of water. 14-2
� 10-DAY [FLSD(p0.05) = 2.38] 11 � 18-DAY [FLSD(p0.05) = 2.60] YELLOW NUTSEDGE � 25-DAY [FLSD(p0.05) = 2.50] CYPERUS ESCULENTUS � 39-DAY [FLSD(p0.05) = 2.42] � � � WEEDS PER POT 9 � � � � � � � � � � 7 � � � � 5 � � � 3 0 250 500 750 1000 METHYL DISULFIDE RATE [MGS/KG SOIL] 2 � 10-DAY [FLSD(p0.05) = 0.59] CRABGRASS � 18-DAY [FLSD(p0.05) = 0.78] DIGITARIA SANGUINALIS � 25-DAY [FLSD(p0.05) = 1.07] � � � 39-DAY [FLSD(p0.05) = 1.14] 1.5 � � � T � � � � O P R � E � � � � P 1 S D E E � W � 0.5 � � � � 0 0 250 500 750 1000 METHYL DISULFIDE RATE [MGS/KG SOIL] Figure 2. Relation between numbers of yellow nutsedge and crabgrass and dosage of methyl disulfide applied by drenching in 1" acre of water in a greenhouse experiment. 14-3
7 � � PIGWEED � 6 AMARANTHUS SPP. � 5 WEEDS PER POT � 10-DAY [FLSD(p0.05) = 1.47] � 18-DAY [FLSD(p0.05) = 1.59] 4 � 25-DAY [FLSD(p0.05) = 1.80] � � � 39-DAY [FLSD(p0.05) = 1.76] 3 � 2 1 � � � � � � � � � � � � � 0 0 250 500 750 1000 METHYL DISULFIDE RATE [MGS/KG SOIL] Figure3. Relation between numbers of pigweed and dosage of methyl disulfide applied by drenching in 1" acre of water in a greenhouse experiment. 14-4
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