Timing and frequency of ethofumesate plus flurprimidol treatments on bermudagrass (Cynodon spp.) suppression in seashore paspalum (Paspalum vaginatum)

Suppression of grass encroachment of one warm-season grass into another spe cies is an important management tool. Two field studies were conducted in G eorgia to determine the timing, rates, and frequency of ethofumesate plus f lurprimidol applications needed to suppress three bermudagrass cultivars an d determine what effects these treatments have on tolerance of three seasho re paspalum cultivars during 1998 and 1999. Tank-mixes of ethofumesate and flurprimidol applied at the 1x rate (1.7 + 0.8 kg/ha) on April 1 suppressed 'TifEagle' bermudagrass effectively (greater than or equal to 78%) by late September. However, the suppression of 'Tifway' bermudagrass (less than or equal to 39%) and 'common' bermudagrass (less than or equal to 67%) was no t acceptable at the same rates and timing. Ethofumesate plus flurprimidol a pplied at the 1x rate in April severely injured all paspalum cultivars 61 t o 65% within a 2- to 6-wk period, but the cultivars recovered to an accepta ble level (less than or equal to 30%) by 10 wk. In most instances, reduced ethofumesate plus flurprimidol rates (1/4x and 1/2x) following the 1x rate in April did not injure the paspalum cultivars as severely as did the initi al 1x rate. However, bermudagrass suppression was improved from the multipl e treatments. When the chemicals were applied initially at the 1x rate and followed by four timely 1/4x rates, bermudagrass suppression by late Septem ber was greater than or equal to 72% for all bermudagrass cultivars, with t he exception of common bermudagrass in 1998 (52%). Maximum injury to the pa spalum cultivars during 1998 and 1999 from the four repeated 1/4x rates ran ged 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 th e 1x or 2x rate on June 30 and followed by a repeated application on July 2 5 did not effectively suppress (less than or equal to 70%) common bermudagr ass either year or Tifway bermudagrass in 1999. However, the suppression of common bermudagrass (greater than or equal to 83%) and Tifway bermudagrass (greater than or equal to 90%) was effective when the chemicals were appli ed initially at the 2x rate on June 30, followed by a 2x rate on July 25 an d a 1x treatment on August 14. TifEagle bermudagrass was effectively suppre ssed (greater than or equal to 85%) when applied initially on June 30 and J uly 25 at the 1x rate. Ethofumesate plus flurprimidol applied once at the 1 x rate on June 30 caused less than or equal to 46% injury to paspalum culti vars. The injury was generally greater than or equal to 50% when the chemic als were applied in two or more applications.