Evaluation of best management practices for bermudagrass (Cynodon spp.) control in zoysiagrass (Zoysia spp.) turf

Abstract

Zoysiagrasses (Zoysia spp.) are a popular choice as turfgrasses in the transition zone of the United States. When managing zoysiagrass, one of the most problematic weeds to control is bermudagrass [Cynodon dactylon (L.) Pers.]. Bermudagrass is typically more competitive and faster growing than any zoysiagrass cultivars currently available, thus contamination is a major problem. Currently, there are few options for turfgrass managers who wish to effectively control bermudagrass in zoysiagrass. Research conducted at Auburn University focused on efficacy of bermudagrass control during turfgrass renovation and selective control in established turfgrass systems. Fairway conversion studies were initiated in May of 2008 and 2009 on an established Tifway bermudagrass stand. Treatments included: glyphosate, EPTC, dazomet, siduron, glyphosate plus ETPC, glyphosate plus dazomet, EPTC plus siduron, and dazomet plus siduron. Results indicate that dazomet plus glyphosate or siduron and EPTC plus glyphosate or siduron were equally effective at controlling Tifway bermudagrass, yielding ≤12% bermudagrass cover 15 weeks after zoysiagrass establishment. Comparing EPTC- and dazomet-alone, EPTC yielded significantly less bermudagrass cover (32%) than dazomet (71%). Field studies were conducted to determine the influence of nitrogen and trinexapac-ethyl on zoysiagrass competiveness with bermudagrass. Trinexapac-ethyl alone was the only treatment to result in decreased Tifway spread throughout the study, relative to the nontreated. In contrast, all rates of nitrogen applied alone resulted in statistically equivalent common bermudagrass spread as trinexapac-ethyl applied alone. In general, nitrogen fertilizer applied with trinexapac-ethyl reduced the efficacy of bermudagrass suppression. Field experiments were conducted to evaluate new aryloxyphenoxypropionate herbicides for the selective control of Tifway bermudagrass in zoysiagrass. Treatments included: clodinafop, triclopyr, clodinafop plus triclopyr, fenoxaprop, fenoxaprop plus triclopyr, metamifop, and metamifop plus triclopyr. Three sequential applications were made at 21-d intervals. Results indicate the addition of triclopyr to clodinafop, fenoxaprop, and metamifop increased bermudagrass control and reduced injury to zoysiagrass. Additive competition experiments were conducted to determine the competitive effects of smooth crabgrass and goosegrass on Zenith zoysiagrass establishment. Zoysiagrass development was reduced at all seeding densities by both weed species 8 weeks after seeding. At the highest neighbor density, goosegrass inhibited zoysiagrass tillering entirely, whereas >20% of zoysiagrass plants developed tillers when grown with smooth crabgrass. Overall, zoysiagrass drymatter yield was reduced from 38 to 99% with increasing weed density. Regression analysis indicated that goosegrass caused greater yield loss per weed unit and maximum yield loss compared to smooth crabgrass.