Use of organic mulch as an alternative to the plastic mulch-methyl bromide system for suppressing purple and yellow nutsedges in tomato production Shabana, Yasser1, Charudattan, R.1, Abou Tabl, A.H.1, Klassen, W.2, Rosskopf, E.3, and Morales-Payan J.P.4 1Department of Plant Pathology, University of Florida, 1453 Fifield Hall, PO Box 110680, Gainesville, FL 32611; 2Tropical REC, 18905 SW 280 St., PO Box 111569, Homestead, FL; 3USDA, ARS, USHRL, 2001 South Rock Road, Fort Pierce, FL 34945; 4Department of Horticulture, University of Puerto Rico - Mayaguez Campus, PO Box 9030, Mayaguez, PR 00681. Introduction Cyperus rotundus and C. esculentus (purple nutsedge and yellow nutsedge, respectively) are among the most serious weed problems in many cropping systems in Florida and other parts of the world. They have been reported to cause yield losses of 20-89% in various horticultural crops. Production systems based on plastic mulch and methyl bromide soil fumigation are used for nutsedge suppression in many conventional vegetable cropping systems. When methyl bromide is fully phased out, the losses due to nutsedges are expected to increase in conventional horticultural crops. Organic production will continue to suffer due to a lack of effective weed control measures. Objective To use organic mulches as an alternative to the plastic mulch-methyl bromide system for suppressing purple and yellow nutsedges in tomato production. Materials & Methods 10 Organic hays (shoot straw of bahiagrass, cogongrass, cowpea, millet, nutsedge, sorghum Sudangrass, sunnhemp, rye, corn, and sugarcane bagasse), four green mulches (cowpea, millet, sorghum Sudangrass, and sunnhemp), and two plastic mulches (black and IRT) were tested for their efficacy in suppressing purple and yellow nutsedge growth in a raised bed tomato (cv. Tygress) field. The beds were fumigated with methyl bromide prior to treatment establishment and a randomized complete block design was used with four replications. Tomato seedlings were transplanted in a single row in all plots at a rate of six tomato seedlings per plot with 18” plant spacing. The following day, nutsedge tubers were seeded, with yellow and purple nutsedge tubers seeded alternately at 1″ depth and 3″ space in two lines parallel to tomato rows (one line on each side with 2″ spacing from tomatoes). Only the plot of weed-free control treatment in each block was not seeded with nutsedge. After seeding the nutsedge tubers, the hay, green or plastic mulches were spread in each plot. Summary The black plastic consistently reduced nutsedge emergence and growth more than the IRT plastic mulch and most of the organic mulches. Green organic mulches, except the green sunnhemp, were more suppressive to nutsedge emergence and growth than hay mulches. IRT plastic was more suppressive to yellow nutsedge than to purple nutsedge. Green sorghum, green millet, and cogongrass hay had the greatest suppressive effect on nutsedge. Sugarcane bagasse and corn hay had the least suppressive effect on nutsedge but had no negative effect on tomato yield. Although cogongrass hay did not promote higher total yield of tomato, it enhanced the yield of extra-large tomato per plant. Results & Discussion Number of nutsedge shoots in cogongrass-mulched vs. bare soil (control) plots Untreated Control Cogongrass Yasser Shabana Dry weight of purple & yellow nutsedge shoots/plot C AB CD A DE E Total yield of tomato per plant BC B Acknowledgements Funding for this research was provided by a USDA-CSREES TSTAR grant. We thank the UF/IFAS Center for Aquatic and Invasive Plants for support. Dry weight of purple nutsedge tubers per plot D BCD Objective: Dry weight of yellow nutsedge tubers per plot 20 40 60 80 100 Black Sorghum-G Millet-G Cogongrass Cowpea-G IRT Corn Sugarcane Bagasse Untreated Control Dry wt. (g) / plot A C BC AB