Investigating low-dose herbicide programs for goosegrass (Eleusine indica) and smooth crabgrass (Digitaria ischaemum) control on creeping bentgrass greens

Abstract

Only four herbicides are registered for smooth crabgrass or goosegrass control on creeping bentgrass golf putting greens. None of the four herbicides control weedy grasses for the entire season or control weeds postemergence when applied once at labeled rates. Three of these have product labels that prohibit repeated use or application during stressful summer conditions. We hypothesized frequently applying herbicides at low doses could provide season-long control of summer grasses while minimizing turf injury. Seven field experiments were conducted on creeping bentgrass putting greens to evaluate various herbicides applied monthly, biweekly, or weekly for postemergence and residual control of goosegrass and smooth crabgrass as well as creeping bentgrass putting green tolerance. Metamifop applied twice monthly at 200 g ai ha−1, topramezone applied eight times weekly at 1.5 g ae ha−1, and siduron applied weekly at 5.6 kg ai ha−1 or four times biweekly at 11 kg ha−1 did not injure creeping bentgrass greater than 10% and maintained creeping bentgrass quality and cover equivalent to nontreated turf. Weekly or biweekly programs of fenoxaprop or quinclorac caused unacceptable injury and quality decline. Metamifop applied monthly and either fenoxaprop program controlled both smooth crabgrass and goosegrass 97 to 99% throughout the growing season. Programs containing either quinclorac or siduron controlled smooth crabgrass 99 to 100% but did not control goosegrass greater than 39%. All topramezone programs controlled smooth crabgrass 69 to 77% and goosegrass 93 to 98%. In additional studies, siduron applied five times biweekly did not injure creeping bentgrass putting greens and controlled smooth crabgrass greater than 90% at seasonal, cumulative rates between 17 and 65 kg ai ha−1. This method of frequent, low-dose herbicide treatment to control smooth crabgrass and goosegrass on golf putting greens is novel and could be legally implemented currently with siduron.

Evaluation of goosegrass response to combinations of topramezone and chlorothalonil

“…Although the mechanism for reduction in topramezone goosegrass control by chlorothalonil-containing products cannot be ascertained through this research, Lancaster et al (2005a) found that chlorothalonil reduces sethoxydim and clethodim absorption by approximately 14% when applied in mixture. A similar reduction in topramezone absorption would be expected to reduce goosegrass control based on rate responses in other studies (Brewer et al 2021). However, researchers have not evaluated topramezone absorption when applied with chlorothalonil.…”

“…However, the reduction in goosegrass control may be potentially overcome by increasing the total number of topramezone applications. Previous studies indicate that multiple topramezone applications are typically needed to control goosegrass (Brewer et al 2021; Cox et al 2017). When topramezone and chlorothalonil applications coincide, applying additional topramezone to overcome the reduced goosegrass control caused by mixing the two products may be more economical than the labor and fuel involved with applying topramezone and chlorothalonil separately.…”

“…Due to this potential for injury, turfgrass managers have employed a variety of methods to mitigate creeping bentgrass injury from topramezone, including frequent low-dose applications. Frequent, low-dose applications of topramezone can effectively control goosegrass without unacceptably injuring creeping bentgrass (Brewer and Askew 2021), but frequent topramezone applications increase the likelihood that herbicide treatments will be mixed with other agrochemicals for practicality.…”

“…Turf managers often mix multiple agrochemicals in a single tank to reduce application costs and compaction caused by spray equipment. Chemical admixtures can alter herbicide uptake, translocation, or metabolism due to changes in plant biochemistry (Akobundu et al 1975), and chemical admixtures have been exploited to decrease turf injury by topramezone (Boyd et al, 2021; Brewer et al 2021). Bermudagrass ( Cynodon dactylon L.…”

“…phytotoxicity was reduced when chelated iron (Boyd et al 2021) was mixed with topramezone. An admixture of metribuzin improved bermudagrass response to topramezone by reducing white discoloration and enabling lower topramezone rates to achieve goosegrass control (Brewer et al 2021). The addition of quinclorac alone, or triclopyr, 2,4-D + dicamba + MCPP + carfentrazone can also reduce bermudagrass bleaching associated with topramezone (Brewer et al 2016; Carroll et al 2021; Cox et al 2017).…”