Abstract: Suppression of grass encroachment of one warm-season grass into another species is an important management tool. Two field studies were conducted in Georgia to determine the timing, rates, and frequency of ethofumesate plus flurprimidol applications needed to suppress three bermudagrass cultivars and determine what effects these treatments have on tolerance of three seashore paspalum cultivars during 1998 and 1999. Tank-mixes of ethofumesate and flurprimidol applied at the 1× rate (1.7 0.8 kg/ha) on April 1 suppressed ‘TifEagle’ bermudagrass effectively (≥ 78%) by late September. However, the suppression of ‘Tifway’ bermudagrass (≤ 39%) and ‘common’ bermudagrass (≤ 67%) was not acceptable at the same rates and timing. Ethofumesate plus flurprimidol applied at the 1× rate in April severely injured all paspalum cultivars 61 to 65% within a 2- to 6-wk period, but the cultivars recovered to an acceptable level (≤ 30%) by 10 wk. In most instances, reduced ethofumesate plus flurprimidol rates (¼× and ½×) following the 1× rate in April did not injure the paspalum cultivars as severely as did the initial 1× rate. However, bermudagrass suppression was improved from the multiple treatments. When the chemicals were applied initially at the 1× rate and followed by four timely ¼× rates, bermudagrass suppression by late September was ≥ 72% for all bermudagrass cultivars, with the exception of common bermudagrass in 1998 (52%). Maximum injury to the paspalum cultivars during 1998 and 1999 from the four repeated ¼× rates ranged from 16 to 45% for ‘Sea Isle 1’, to 33 to 37% for ‘Sea Isle 2000’, and 21 to 52% for ‘K-3’. Ethofumesate plus flurprimidol applied initially at the 1× or 2× rate on June 30 and followed by a repeated application on July 25 did not effectively suppress (≤ 70%) common bermudagrass either year or Tifway bermudagrass in 1999. However, the suppression of common bermudagrass (≥ 83%) and Tifway bermudagrass (≥ 90%) was effective when the chemicals were applied initially at the 2× rate on June 30, followed by a 2× rate on July 25 and a 1× treatment on August 14. TifEagle bermudagrass was effectively suppressed (≥ 85%) when applied initially on June 30 and July 25 at the 1× rate. Ethofumesate plus flurprimidol applied once at the 1× rate on June 30 caused ≤ 46% injury to paspalum cultivars. The injury was generally ≥ 50% when the chemicals were applied in two or more applications.
Nomenclature: Ethofumesate; flurprimidol, α-(1-methyl-ethyl)-α-[4-(trifluoromethoxy)-phenyl]-5-pyrimidine-methanol; bermudagrass, Cynodon dactylon (L.) Pers. #3, CYNDA ‘common’; hybrid bermudagrass, Cynodon transvaalensis × C. dactylon ‘Tifway’, ‘TifEagle’; seashore paspalum, Paspalum vaginatum Swartz #3 PASVA ‘Sea Isle 1’, ‘Sea Isle 2000’, ‘K-3’.
Additional index words: Turfgrass injury, turfgrass tolerance.
