Effects of Soil vs. Foliar Application of Mesotrione on Yellow Nutsedge and Large Crabgrass James D. McCurdy, J. Scott McElroy, and Greg K. Breeden; Plant Sciences Department, The University of Tennessee, Knoxville, TN Introduction Yellow nutsedge (Cyperus esculentus L.) and large crabgrass (Digitaria sanguinalis (L.) Scop.) are problematic turf weeds. Mesotrione, a carotenoid biosynthesis inhibitor, is currently being evaluated for use in turfgrass systems. Mesotrione controls large crabgrass and varies in its control of yellow nutsedge. Young et al. (1999) demonstrated that foliar applications of mesotrione were more effective than soil applications. However, it is necessary to evaluate the soil activity of mesotrione in these turf weeds. Table 1. Foliar, soil, and soil + foliar applied mesotrione control of yellow nutsedge and large crabgrass 28 and 56 DAT. Data was subjected to ANOVA (P = 0.05). Means were separated by Fisher’s protected LSD (P = 0.05).   Yellow Nutsedge Large Crabgrass %Control Rate Placement 28 DAT 56 DAT 0.14 kg/ha Foliar 39 b 28 c 19 e 13 d Soil 57 a 81 a 60 c 91 ab Soil + Foliar 41 b 54 b 38 d 62 c 0.28 kg/ha 64 b 71 bc 58 a 96 a 71 b 90 ab 65 a 84 a 83 a 98 a Objective Compare the effects of foliar, soil, and soil + foliar applied mesotrione on yellow nutsedge and large crabgrass. Materials and Methods Greenhouse studies were conducted at the University of Tennessee, Knoxville, during fall 2006 and spring 2007. Weeds were grown under natural lighting in 12 cm diameter plastic pots (3 plants/pot) containing native silt-loam soil [Sequatichie loam soil (fine-loamy, siliceous, semi-active, thermic Humic Hapludult) with pH 6.2 and 2.1% organic matter]. Plants were overhead irrigated twice daily and were fertilized (Howard Johnson’s 20-20-20 plus minors) on a bi-weekly basis prior to treatment and resuming 7 days after treatment (DAT). Mesotrione was applied at 0.14 or 0.28 kg ai/ha plus 0.25% v/v NIS to pots in three ways: foliar alone, soil alone, or soil + foliar. Foliar alone and soil + foliar treatments were applied with a CO2 pressurized sprayer at 280 L/ha. Soil of foliar alone treated pots was covered with 1.0 cm of peat moss to intercept the mesotrione before it reached the soil surface. Peat moss was removed 15 min after application. For soil applications, the amount of mesotrione that normally contacts the soil was diluted in 10 mL of water and syringed onto the soil. Plants were sub-irrigated until 7 DAT; after which, overhead irrigation resumed. Yellow nutsedge and large crabgrass injury was evaluated visually for phytotoxicity on a 0 (no phytotoxic response) to 100 (complete plant death) % scale at 28 and 56 DAT. At 28 DAT, plant foliage was harvested by clipping plants 1.5 cm above the soil. Plants were subsequently allowed to grow new foliage. At 56 DAT, foliage was harvested to the soil level and roots were washed free of soil. All plant biomass was oven dried and weighed. Data was subjected to ANOVA (P = 0.05). Means were separated by Fisher’s protected LSD (P = 0.05). Table 2. Foliar dry weights (DW) 28 and 56 DAT and root DW 56 DAT of yellow nutsedge and large crabgrass treated with mesotrione applied foliar, soil, and soil + foliar at either 0.14 and 0.28 kg/ha. Data was subjected to ANOVA (P = 0.05). Means were separated by Fisher’s protected LSD (P = 0.05).   Yellow Nutsedge Large Crabgrass Foliar DW (g) Root DW (g) Foliar Dry Weight (g) Root DW(g) 28 DAT 56 DAT Rate Placement Fall Spring 0.14 kg/ha Foliar 0.5 b 3.1 cb 0.2 a 5.3 ab 1.1 b 2.5 abc 0.8 b 7.0 b 0.4 a 4.8 a 9.1 a Soil 3.9 b 0.0 b 4.4 ab 0.7 b 3.9 ab 0.0 c 2.6 d 0.9 b Soil + Foliar 3.1 b 3.4 b 2.8 a 1.3 bc 0.3 c 1.4 d 0.1 b 1.2 b 0.2 c 0.28 kg/ha 0.4 b 1.3 cd 2.9 b 0.1 c 4.5 cb 1.5 ab 4.5 ab 0.1 bc 2.4 d 2.5 ab 1.6 b 1.0 d 1.0 b 0.6 bc 3.0 cd Non Treated 2.5 a 6.3 a 9.8 a 6.0 a 2.0 c 5.0 a 1.3 a 5.4 ab Results Mesotrione treatments applied at 0.28 kg/ha were more effective than treatments applied at 0.14 kg/ha at controlling both yellow nutsedge and large crabgrass. Soil and soil + foliar applications controlled yellow nutsedge and large crabgrass greater than foliar alone application. Mesotrione control of yellow nutsedge and large crabgrass was greater 56 DAT than 28 DAT. Figure 1. Yellow nutsedge and large crabgrass response 56 DAT to soil, foliar, and soil + foliar applied mesotrione at 0.14 and 0.28 kg/ha. 0.14 kg/ha 0.28 kg/ha Control Foliar Soil Soil + Foliar Yellow Nutsedge Large Crabgrass Conclusion Mesotrione absorbed by roots from soil is required for complete control of both yellow nutsedge and large crabgrass. Mesotrione application methods that target foliage alone may result in inadequate control of yellow nutsedge and large crabgrass. Future Research Examine the impact of soil moisture on the root absorption of mesotrione. Study the effects of post-application precipitation/irrigation on the efficacy of mesotrione. Explore the efficacy of root absorbed mesotrione in other weeds and turfgrass species. Sources Young, B.G., B.C. Johnson, and J.L. Matthews. 1999. Preemergence and sequential weed control with mesotrione in conventional corn. North Cent. Weed Sci. Res. Rep. 56: 226-227. Mitchell, G., D.W. Bartlett, T.E.M. Fraser, T.R. Hawkes, D.C. Holt, J.K. Townson, and R.A. Wichert. 2001. Mesotrione: a new selective herbicide for use in maize. Pest Manage. Sci. 57: 120-128.