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Soil Fumigation after Methyl Bromide: Managing Concentrations of Drip-Applied Metam Potassium for Nutsedge Control
http://edis.ifas.ufl.edu/ ( Publisher's URL )
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Permanent Link: http://ufdc.ufl.edu/IR00000904/00001
 Material Information
Title: Soil Fumigation after Methyl Bromide: Managing Concentrations of Drip-Applied Metam Potassium for Nutsedge Control
Physical Description: Fact Sheet
Creator: Santos, Bielinski M. 1968-
Gilreath, J. P (James Preston), 1947-
Publisher: University of Florida Cooperative Extension Service, Institute of Food and Agriculture Sciences, EDIS
Place of Publication: Gainesville, Fla.
Publication Date: 2012
 Notes
Abstract: This 2-page fact sheet presents the results of studies conducted to determine the influence of metam potassium concentrations on purple nutsedge control.
Acquisition: Collected for University of Florida's Institutional Repository by the UFIR Self-Submittal tool. Submitted by Diana Hagan.
Publication Status: Published
General Note: "Publication #HS1201"
 Record Information
Source Institution: University of Florida Institutional Repository
Holding Location: University of Florida
Rights Management: All rights reserved by the submitter.
System ID: IR00000904:00001

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HS1201 Soil Fumigation after Methyl Bromide: Managing Concentrations of Drip-Applied Metam Potassium for Nutsedge Control1Bielinski M. Santos and James P. Gilreath2 1. This document is HS1201, one of a series of the Horticultural Sciences Department, Florida Cooperative Extension Service, Institute of Food and Ag ricultural Sciences, University of Florida. Original publication date April 2012. Visit the EDIS website at http://edis.ifas.u.edu 2. Bielinski M. San tos, assistant professor, and James P. Gilreath, professor, Horticultural Sciences Department, UF/IFAS Gulf Coast Research and Education Center, Wimauma, FL 33598. All chemicals should be used in accordance with directions on the manufacturers label. Use pesticides safely. Read and follow directions on the manufacturers label.The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or aliations. U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A&M University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Millie Ferrer-Chancy, Interim DeanIsothiocyanate-Generator Fumigantse search for methyl bromide alternatives has been a vast source of research during the last two decades. Hundreds of trials have been conducted nationwide to examine the ecacy of dierent soil fumigants on soilborne pests in polyethylene-mulched tomato (Lycopersicon esculentum ), pepper (Capsicum annuum ), strawberry (Fragaria x ananassa ), cucurbits, cut ower, and other commodities. Although a great deal of progress has been achieved in this eld, currently there is not a single molecule to replace methyl bromide. Instead, ongoing research focuses not only on the ecacy of the combination of certain fumigants and herbicides, but also on application techniques and formulations. Purple (Cyperus rotundus ) and yellow (C. esculentus) nutsedge are the most troublesome weeds to control in polyethylene-mulched vegetable crops and have the ability to emerge through the mulch, causing yield and quality losses (Figure 1). In the past, methyl bromide applications were used to eectively control nutsedge populations below damage thresholds. However, other fumigants do not have consistent ecacy against these weeds. Isothiocyanate-generator fumigants break down as either allyl or methyl isothiocyanate (ITC), which are potent biocides. Commercially, they can be found either as synthetic active ingredients, such as dazomet, metam sodium, and metam potassium, or as natural extracts from mustard seed and oil. ey are formulated mostly as solid granules, powder, and liquid products. e solid formulations need to be incorporated into the soil to initiate activation. e fumigants metam sodium and metam potassium are Figure 1. Nutsedge sprouting through white polyethylene mulch. Credits: B.M. Santos

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2 available in liquid formulations, which provide application exibility because they can be either directly sprayed on the soil and incorporated or drip injected. In Florida, the ecacy of these fumigants against soilborne diseases, nematodes, and weeds has been tested with mixed results, especially with regard to nutsedge (Cyperus spp.) control in vegetables and strawberry. An extensive revision of that research is available elsewhere and escapes the scope of this publication. However, various reports have suggested that performance of drip-applied metam fumigants against nutsedge can improve by applying concentrations that expose sprouting tubers to lethal rates. ese concentrations are the result of combinations of fumigant rates and water volumes. us, studies were conducted to determine the inuence of metam potassium concentrations on purple nutsedge control. Metam Potassium Concentration LevelsStudies were conducted in deep, sandy soil at the University of Florida. e soil was low in organic matter (%) and had a pH of 7.3. Selected elds were heavily infested with purple nutsedge ( plants/2). Planting beds were 8 inches high by 28 inches wide and covered with low-density polyethylene mulch (1.25 mil thick). Two drip irrigation lines (0.45 gal/100 per min; T-Tape Systems) were buried 1 inch deep in the bed center under the mulch lm. Irrigation emitters were 12 inches apart. Besides drip irrigation, continuous subsurface irrigation maintained the water table at 18 inches deep in order to reduce water stress on weed populations. e applied metam potassium concentrations were 2000, 3000, 4000, 5000, and 6000 ppm, and these were obtained by mixing a rate of 120 gal/acre with 3, 2, 1.5, 1.2, and 1 acre-inch/acre of water, respectively. A nonfumigated control was added. Purple nutsedge densities were determined at 4, 6, and 10 weeks aer treatment (WAT). A nontreated control was included. Metam potassium was injected with electric water pumps, which were connected to mixing tanks where the solutions were prepared and constantly agitated. Purple nutsedge was counted at 2, 10, and 15 WAT over the entire experimental area. e results indicated that metam potassium concentrations aected purple nutsedge densities at 4, 6, and 10 WAT. At 4 WAT, purple nutsedge densities decreased as metam potassium concentrations increased, with a maximum weed density of 12 plants/2 when no fumigant was applied and declining to 3.5 and 1 plants/2 when metam potassium concentrations reached 3000 and 6000 ppm, respectively (Figure 2). Two weeks later, a similar relationship between metam potassium concentration and purple nutsedge densities persisted. However, in the nonfumigated control, weed density reached 23 plants/2 and decreased to 9 and 4 plants/2 with 3000 and 6000 ppm, respectively (Figure 2). A linear regression model characterized the purple nutsedge density response to applied concentrations of metam potassium at 10 WAT, which translates into approximately 42% and 85% nutsedge control. SummaryPrevious studies on purple nutsedge interference in vegetable crops have shown that a density of 5 plants/2 causes relatively marginal yield reductions in tomato and bell pepper, whereas a nutsedge density of more than 10 plants/2 can reduce tomato yield by 51%. In this study, application of metam potassium decreased purple nutsedge populations, resulting in densities below 5 plants/2 with 6000 ppm for up to 10 WAT. However, this concentration can be achieved with a metam potassium rate of 60 gal/ acre, which is the labeled rate, dissolved in 0.5 acre-inch/ acre of water. is is within the recommended rates in the label of the commercial formulation of the product. e results indicated that with the appropriate metam potassium concentrations and uniform delivery throughout planting beds, it is likely to cause longer and more eective exposure of purple nutsedge tubers and other underground structures to the fumigant, thus increasing its ecacy. Figure 2. Eects of metam potassium concentrations on purple nutsedge (Cyperus rotundus) densities at 4, 6, and 10 weeks after treatment. Credits: B.M. Santos