Evaluation of Yellow Mustard Seed Meal for Weed Control D.T. Earlywine, T.C. Teuton, J. C. Sorochan, B. S. Fresenburg, R. J. Smeda, and L. E. Sweets Division of Plant Sciences, University of Missouri, Columbia, MO and Department of Plant Sciences, University of Tennessee, Knoxville, TN INTRODUCTION________ ______ _____________ Since the early 1990’s, methyl bromide production has been slowly phased out by the Environmental Protection Agency due to ozone depletion. With the phase out, turf professionals have been searching for a soil fumigant that will effectively control soil pathogens, diseases, insects, and weeds. Many mustard species (Brassica spp.) have fumigant characteristics. Mustard seed meals and/or mustard green manures release gaseous allyl isothiocyanates (AITC) when incorporated into a moist soil profile (Matthiessen and Kirkgarrd 2006). AITC is similar to methyl isothiocyanate, the active ingredient in dazomet and metam-sodium (Neal 1999; Matthiessen and Kirkegarrd 2006). In previous research, mustard seed meals and/or mustard green manures have suppressed germination of chickweed, Kochia, shephard’s-purse, green foxtail, large crabgrass, Texas panicum, and sicklepod (Al-Khatib et al. 1997; Norsworthy and Meehan 2005). However, little research has been conducted evaluating weed control in turfgrass systems using yellow mustard (Sinapis alba L.) seed meal as a fumigant. OBJECTIVES _______________ ___ To evaluate control of common turfgrasses and weed species using yellow mustard seed meal (MSM) as a fumigant. MATERIALS AND METHODS_______________ ___ Greenhouse experiments were conducted University of Missouri-Columbia Ashland Road Greenhouse Facility during the fall of 2006 and summer of 2007. Each experiment had 4 replications and was conducted twice. Treatments, listed in Table 1, include MSM at increasing rates from 170 to 3360 kg/ha, an untreated check, and dazomet as an industry standard. All treatments were mixed thoroughly with 7900 cm3 of Menfro silt loam soil and were put in pots that were 51-cm long, 31-cm wide, and 6-cm deep (Figure 1). Turfgrass and weeds were planted 0.5-cm deep in eight separate rows that were 25-cm long. Following planting, each pot was irrigated and the tarped treatments were immediately sealed in clear polyurethane plastic bags. Untarped treatments were watered daily for the next week to maintain adequate soil moisture and to insure soil capping. After one week, all polyurethane bags were removed from the tarped treatments. All pots were then irrigated as needed to maintain adequate soil moisture for germination and emergence. Plants were counted four weeks after planting. During the fall of 2006 and summer of 2007, the greenhouse was maintained at 22 C and 29 C ± 5 C. Data were analyzed in SAS using Mixed model analysis. Trials, treatments, and there interaction were significant for each turfgrass and weed species, therefore data were separated by trial. RESULTS AND DISCUSSION_____ _____________________ In the first experiment in 2006, tarped MSM treatments at 1680 kg/ha controlled all weeds >73%, except tall fescue at 1680 and 2020 kg/ha and perennial rye at 1680 and 3030 kg/ha (Table 1).  Also in 2006, the untarped MSM treatments were inconsistent; however untarped MSM at 3360 kg/ha controlled all weeds >60%.  In 2007, bermudagrass control with MSM was no different from the untreated untarped (Table 1). However, MSM controlled large crabgrass >72 % at rates >2700 kg/ha. Dazomet controlled all weeds >97% (Table 1). __________________________ ______________________ Table 2. Control, based on plant populations, of turfgrass and weed species four weeks after planting using mustard seed meal (MSM) as a soil fumigant in the second experiment during 2006 and 2007. a Abbreviations: CYNDA = ‘Riviera’ bermudagrass , DIGSA = large crabgrass, FESAR = ‘Rembrandt’ tall fescue, LOLPE = ‘Evening Shade’ perennial ryegrass, LSD= Fisher’s least significant difference, MSM= yellow mustard seed meal, PLALA = narrow leaf plantain, POAAN = annual bluegrass, STEME = common chickweed, TRFRE = white clover. b Plant populations were normalized to percent control based on the untreated untarped mustard seed meal treatments. The untreated untarped plants populations were: bermudagrass = 20, crabgrass = 8, tall fescue = 33, perennial ryegrass = 37, narrow leaf plantain = 24, annual bluegrass = 36 , common chickweed = 25 , and white clover = 16. In the second experiment in 2006, tarped MSM treatments >1350 kg/ha provided >73% control for all weeds except white clover (63%) at 1680 kg/ha.  Also, the untarped treatments >2350 kg/ha controlled weeds >73% except white clover (< 60%) . In 2007, bermudagrass was not controlled by any MSM treatment (Table 2). However, large crabgrass control was inconsistent (<73%) for all MSM treatments. Similar to the first experiment, dazomet controlled all species 100%.  In previous research, large crabgrass plant densities were reduced 98 and 100% with aliphatic isothiocyanates such as allyl and 3-methylthiopropyl isothiocyanate (Norsworthy and Meehan, 2005). Although crabgrass was not controlled as well in our experiments, MSM shows promise as a soil fumigant. Conclusion__________ ____________________________ Turfgrass and weed control increased as yellow MSM increased from 0 to 3360 kg/ha, with the exception of bermudagrass. Overall, the standard dazomet provided the highest control. However, weed control with higher MSM rates was not different for many of the species tested. Also, tarped treatments tended to control weeds better than untarped treatments. MSM has potential as a soil fumigant, however more testing is needed to determine it’s efficacy in field situations, establish use rates, and crop plant-back intervals. Literature Cited__________________________________ Al-Khatib, K., C. Libbey, and R. Boydston. 1997. Weed suppression with Brassica green manure crops in green pea. Weed Sci. 45:439-445. Matthiessen, J.N., J.A. Kirkegaard. 2006. Biofumigation and enhanced biodegradation: opportunity and challenge in soilborne pest and disease management. Critical Reviews in Plant Sci. 25:235-265. Neal, N. J. 1999. Weed management in conifer seedbeds and transplant beds. North Carolina State University Horticulture Information Leaflets. HIL-449. Norsworthy, J.K. and J.T. Meehan. 2005. Herbicidal activity of eight isothiocyanates on Texas panicum (Panicum texanum), large crabgrass (Digitaria sanguinalis), and sicklepod (Senna obtusifolia). Weed Sci. 53:515-520. Treatment Rate Tarped/ _________________________________ 2006 ________________________________ ______ 2007 ______ (kg/ha) Untarped FESAR LOLPE PLALA POAAN STEME TRFRE CYNDA DIGSA ___________________________________________ Controlb________________________________________________ Untreated - MSM 1350 66 68 43 59 58 -39 -15 27 2350 93 82 81 86 60 20 33 3360 88 95 73 80 52 2 62 Dazomet 390 100 Tarped 30 47 22 5 -42 -25 170 -2 26 34 13 45 -26 -52 340 23 53 55 -129 -71 -5 670 38 48 39 44 -105 12 1010 49 42 56 -51 77 90 83 76 -47 57 1680 87 85 63 -1 2020 96 98 -10 89 75 91 7 2700 84 -6 3030 99 92 17 -9 65 100f LSD0.05 18 16 21 24 46 Table 1. Control, based on plant populations, of turfgrass and weed species four weeks after planting using mustard seed meal (MSM) as a soil fumigant in the first experiment during 2006 and 2007. a Abbreviations: CYNDA = ‘Riviera’ bermudagrass , DIGSA = large crabgrass, FESAR = ‘Rembrandt’ tall fescue, LOLPE = ‘Evening Shade’ perennial ryegrass, LSD= Fisher’s least significant difference, MSM= yellow mustard seed meal, PLALA = narrow leaf plantain, POAAN = annual bluegrass, STEME = common chickweed, TRFRE = white clover. b Plant populations were normalized to percent control based on the untreated untarped mustard seed meal treatment. The untreated untarped plant populations were: bermudagrass = 20, crabgrass = 9, tall fescue = 47, perennial ryegrass = 47, narrow leaf plantain = 44, annual bluegrass = 71, common chickweed = 44, and white clover = 93. Treatment Rate Tarped/ _______________________________________ 2006 _____________________________________ _________ 2007 ________ (kg/ha) Untarped FESAR LOLPE PLALA POAAN STEME TRFRE CYNDA DIGSA _______________________________________________ Controlb________________________________________________ Untreated - MSM 1350 20 28 93 13 58 10 42 2350 51 52 70 77 82 68 -3 44 3360 66 60 90 73 6 81 Dazomet 390 100 97 Tarped 1 7 35 4 17 -45 170 -5 34 24 40 -13 56 340 -10 9 32 -23 670 -6 3 30 -123 39 1010 61 47 -46 69 29 87 85 -54 78 1680 54 43 94 92 79 -15 67 2020 63 76 89 99 98 -29 2700 75 95 83 72 3030 88 5 96 -19 LSD0.05 19 15 22 Figure 1. Various stages of the first greenhouse experiment. Figure 2. Comparisons of tarped and untarped treatments in the first experiment between a) untreated check, b) MSM at 3360 kg/ha, and c) Dazomet at 392 kg/ha. a. b. c. Tarped Untarped Turfgrass Science University of Missouri-Columbia