Submitted to: Pest Management Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/29/2006
Publication Date: 4/2/2007
Citation: Candole, B.L., Csinos, A.S., Wang, D. 2007. Distribution And Efficacy Of Drip-Applied Metam-Sodium Against The Survival Of Rhizoctonia Solani And Yellow Nutsedge In Plastic-Mulched Sandy Soil Beds. Pest Management Science, 63:468-475. Interpretive Summary: Increasing the rate of metam-sodium application increased the methyl isothiocyanate levels in treated beds but did not increase this to a level that was biologically active against R. solani and yellow nutsedge at sites laterally away from the point of application (or towards the bed shoulders). In the absence of methyl bromide, the most promising alternative fumigants that possess all the properties of methyl bromide are methyl isothiocyanate, 1,3-dichloropropene and chloropicrin. As such they are widely used for a number of target pests and diseases, either alone or in combinations with other alternatives. These chemicals have lower vapor pressures than methyl bromide, so they are primarily distributed in the soil bed by water movement. Because of this, they have been widely studied for improved efficacy and improved distribution through drip irrigation systems. Previously published research data suggested improved efficacy arising from bed configuration (i.e. narrower beds) and drip tape configuration (i.e. emitter spacing and number of drip tapes per bed) for pest and disease control. With the reluctance of crop growers to incorporate this information into their production systems, additional work is needed to (1) enhance the lateral distribution of the active material at effective concentrations throughout the soil bed and (2) educate growers on the benefits of incorporating useful previous research data in terms of improved efficacy in controlling pests and diseases.
Technical Abstract: The effects of metam-sodium application rate on soil residence time, spatial and temporal distributions of methyl isothiocyanate and pest control efficacy were studied in a Georgia sandy soil. Metam-sodium 420 gL-1 SL was drip applied at rates of 147 and 295Lha-1 in plastic-mulched raised beds. Methyl isothiocyanate concentrations in soil air space were monitored from four preselected sites: 10 and 20 cm below the emitter, and 20 and 30cm laterally away from the emitter at 3, 12, 24, 48, 72, 120 and 240 h after chemigation. A higher rate of metam-sodium application resulted in higher methyl isothiocyanate concentrations in the soil. Highest methyl isothiocyanate concentrations were found at 20cm below the emitter, and lowest at 30 cm laterally away from the emitter. Methyl isothiocyanate concentrations decreased with time and distance from the emitter. Lower methyl isothiocyanate concentration × time product values at 20 and 30cm away from the emitter resulted in lower mortalities of Rhizoctonia solani Kuhn and yellow nutsedge (Cyperus esculentus L.). The results monstrated that methyl isothiocyanate can be delivered at lethal doses with drip-applied water downward within the beds. Lateral diffusion of methyl isothiocyanate from the point of application did not reach biologically active concentrations to affect the survival of R. solani or yellow nutsedge. Further studies on the lateral distribution of methyl isothiocyanate in sandy soils are needed to circumvent this limitation.