Summer annual grassy weeds such as goosegrass (Eleusine indica L. Gaertn.) continue to be problematic to control selectively with postemergence (POST) herbicides within turfgrass stands. In recent years, reduced performance by certain herbicides (e.g., foramsulfuron), cancellation of goosegrass-specific herbicides (e.g., diclofop-methyl), and cancellation and/or severe use reductions of other herbicides [e.g., monosodium methanearsonate (MSMA)] have limited the options for satisfactory control and maintenance of an acceptable (≤30% visual turfgrass injury) turfgrass quality. Currently available herbicides (e.g., topramezone and metribuzin) with goosegrass activity typically injure warm-season turfgrass species. The objectives of this research were to evaluate both ‘Tifway 419’ bermudagrass [Cynodon dactylon (L.) Pers. ×Cynodon transvaalensis Burtt-Davy] injury after treatment with POST herbicides, and to determine whether irrigating immediately after application reduces turfgrass injury. Treatments were control (± irrigation); topramezone (Pylex 2.8C; ± irrigation); carfentrazone + 2,4-D + dicamba + 2-(2-methyl-4-chlorophenoxy) propionic acid (MCPP) (Speedzone 2.2L; ± irrigation); carfentrazone + 2,4-D + dicamba + MCPP in combination with topramezone (± irrigation); metribuzin (Sencor 75DF; ± irrigation); mesotrione (Tenacity 4L; ± irrigation); simazine 4L (±irrigation); and mesotrione + simazine (± irrigation). Irrigated treatments were applied immediately with a hand hose precalibrated to apply 0.6 cm or 0.25 inch (≈6.3 L). Visual turfgrass injury for combined herbicide treatments for the irrigated plots was 6% 4 days after treatment (DAT), 12% 1 week after treatment (WAT), 17% 2 WAT, and 6% 4 WAT, whereas nonirrigated plots had turfgrass injury of 14% at 4 DAT, 31% 1 WAT, 35% 2 WAT, and 12% 4 WAT. Irrigated pots had normalized differences vegetative indices (NDVI) ratings of 0.769 at 4 DAT, 0.644 at 1 WAT, 0.612 at 2 WAT, and 0.621 at 4 WAT, whereas nonirrigated plots had the lowest (least green) turfgrass NDVI ratings of 0.734 at 4 DAT, 0.599 at 1 WAT, 0.528 at 2 WAT, and 0.596 at 4 WAT. These experiments suggest turfgrass injury could be alleviated by immediately incorporating herbicides through irrigation.
Robert Andrew Kerr, Lambert B. McCarty, Philip J. Brown, James Harris, and J. Scott McElroy
Robert Andrew Kerr, Lambert B. McCarty, Matthew Cutulle, William Bridges, and Christopher Saski
Goosegrass (Eleusine indica L. Gaertn.) is a problematic C4 weedy grass species, occurring in the warmer regions of the world where it is difficult to selectively control without injuring the turfgrass. Furthermore, control efficacy is affected by plant maturity. End-user options for satisfactory goosegrass control has decreased; thus, the need for developing management techniques to improve the selectivity of POST goosegrass control options in turfgrass systems is ever increasing. One possible means of providing control, yet maintaining turf quality is immediately incorporating applied products via irrigation. Greenhouse and field trials were conducted in Pickens County, SC, with the objectives of 1) evaluating turfgrass injury following use of POST goosegrass control options; 2) assessing if irrigating (0.6 cm) immediately following the herbicide application reduces injury of ‘Tifway 419’ bermudagrass [Cynodon dactylon (L.) Pers. × Cynodon transvaalensis Burtt-Davy]; and 3) determining if immediate irrigation influences goosegrass control at one- to three-tiller and mature growth stage. Following the application of herbicide treatments, irrigation was applied (+) or not applied (−). Treatments included the following: control (+/− irrigation); topramezone at 12.3 g a.i./ha (+/− irrigation); metribuzin at 420 g a.i./ha (+/− irrigation); and topramezone plus metribuzin (+/− irrigation) at 12.3 and 420 g a.i./ha. Irrigation treatment had minimum effect on greenhouse-grown goosegrass biomass, all treatments provided >85% control of 1- to 3-tiller goosegrass plants. However, control for mature plants was <50% for topramezone- and 60% to 70% for metribuzin-containing treatments. In field studies, at 1 week after treatment (WAT), the irrigated metribuzin and topramezone plus metribuzin had ≈37% and ≈16%, respectively, less goosegrass control vs. nonirrigated treatments. At 2WAT, irrigated metribuzin and irrigated topramezone plus metribuzin–treated plots, had ≈50% less mature goosegrass control vs. nonirrigated treatments. Irrigated herbicide treatments, however, experienced ≈23% less turfgrass injury at this time. At 4 WAT, irrigated metribuzin- and irrigated topramezone plus metribuzin–treated plots experienced reduced mature goosegrass control by ≈65% and ≈59%, respectively. Overall, incorporating POST herbicide applications via 0.6 cm of irrigation reduced turfgrass injury by at least 20% for all herbicide treatments, while maintaining goosegrass control.
Jeffery W. Marvin, Robert Andrew Kerr, Lambert B. McCarty, William Bridges, S. Bruce Martin, and Christina E. Wells
Clarireedia jacksonii sp. nov. formerly Sclerotinia homoeocarpa F.T. Bennett, one of the causal agents of dollar spot, is the most widespread pathogen in turfgrass systems. Dollar spot (DS) affects both cool- and warm-season grasses, during a wide range of environmental conditions. Field studies were conducted at Clemson University, Clemson, SC, on a creeping bentgrass [Agrostis stolonifera L. var. palustris (Huds) cv. Crenshaw] putting green for 2 consecutive years from August to October in year 1 and July to September in year 2. The objective of the studies was to evaluate biological control agents (BCAs) and synthetic fungicides at reduced rates for their efficacy controlling dollar spot. Four replications of 1.5 × 1.5-m plots were used in the experimental design. Treatments included the following: Bacillus subtilis (BS); plant extract oils (EO) including clove oil + wintergreen oil + thyme oil; extract of Reynoutria sachalinensis (RS); Bacillus licheniformis (BL); chlorothalonil (CL); and azoxystrobin + propiconazole (AzP). Synthetic fungicides were used at reduced rates in combination with biological control agents, to evaluate curative control efficacy of various combinations. All reduced synthetic programs, except CL + EO, provided acceptable disease severity (≤15%) at the end of year 1 and acceptable (≥7) turfgrass visual quality. Azoxystrobin + propiconazole, CL, AzP + BL, AzP + EO, AzP + BS all provided ≤15% disease severity and ≥7 visual turfgrass quality 14 days after the last application in year 2.