Influence of posttreatment irrigation timings and herbicide placement on bermudagrass and goosegrass (Eleusine indica) response to low-dose topramezone and metribuzin programs

Abstract

Immediate, post-treatment irrigation has been proposed as a method to reduce hybrid bermudagrass [Cynodon dactylon (L.) Pers. x Cynodon transvaalensis Burtt Davy] phytotoxicity from topramezone. Immediate irrigation is impractical since it would take a turfgrass sprayer 10 to 15 minutes to cover an average golf course fairway or athletic field. There is also insufficient evidence regarding how post-treatment irrigation, immediate or otherwise, influences mature goosegrass [Eleusine indica (L.) Gaertn.] control from topramezone or low-dose topramezone plus metribuzin programs. We sought to investigate bermudagrass and E. indica response to immediate, 15-minute, and 30-minute post-treatment irrigation compared to no irrigation following topramezone at 12.3 g ae ha−1, the lowest labeled rate, or topramezone at 6.1 g ha−1 plus metribuzin at 210 g ai ha−1. We also evaluated placement of each herbicide and their combination on soil, foliage, and soil plus foliage to help elucidate the mechanisms involved in differential responses between species and herbicide mixtures. Responses were largely dependent on trial due to bermudagrass injury from high-dose topramezone being nearly eliminated by immediate irrigation in one trial and only slightly affected in another. When post-treatment irrigation was postponed for 15 or 30 minutes, topramezone alone injured bermudagrass unacceptably in both trials. Bermudagrass was injured less by low-dose topramezone plus metribuzin than by high-dose topramezone. All post-treatment irrigation timings reduced E. indica control compared to no post-treatment irrigation. The herbicide placement study suggested that topramezone control of E. indica is highly dependent on foliar uptake and phytotoxicity of both bermudagrass and E. indica is greater from topramezone than metribuzin. Thus, post-treatment irrigation likely reduces topramezone rate load with a concomitant effect on plant phytotoxicity of both species. Metribuzin reduced 21-d cumulative clipping wt and tiller production of plants, and this may be a mechanism by which it reduces foliar white discoloration from topramezone.

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.…”

“…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).…”

“…An admixture of metribuzin improved bermudagrass response to topramezone by reducing white discoloration and enabling lower topramezone rates to achieve goosegrass control ). The addition of quinclorac alone, or triclopyr, 2,4-D þ dicamba þ MCPP þ carfentrazone can also reduce bermudagrass bleaching associated with topramezone (Brewer et al 2016;Carroll et al 2021;Cox et al 2017). Creeping bentgrass turf was injured less when topramezone was mixed with the herbicide safener cloquintocet-mexyl (Elmore et al 2015).…”