Russell, D.P.1; Quick, H.B.2; Byrd Jr., J.B.3
1Assistant Research and Extension Professor, Alabama Cooperative Extension System, Auburn University, Belle Mina, AL, 35615
2Extension Associate I, Mississippi State University, Mississippi State, MS, 39762
3Extension/Research Professor, Mississippi State University, Mississippi State, MS, 39762


Dallisgrass (Paspalum dilatatum Poir.) has potential as a desirable livestock forage, but is often viewed as an unwanted weed in high quality bermudagrass (Cynodon dactylon (L.) Pers.) systems. Nonselective chemical control options are available, but the potential loss of desirable species proves too great to utilize in-season applications. Prior field observations have found dallisgrass to maintain green leaf tissue longer into the winter months compared to bermudagrass, thus providing a possible window for effective control with minimal injury to bermudagrass. Using cooling degree days (CDD) beginning August 1 and/or field observations are two methods that exist in the mid-South for determining that application window. Therefore, the aim of this study was to evaluate effects of herbicide and application timing on dallisgrass when applied following autumn frost and bermudagrass dormancy, but prior to dallisgrass quiescence. A two (application time) by four (treatment) factorial arrangement was established in a randomized complete block design with three replications near Starkville, MS in 2018. Applications were made following at least two frosts (below 0 °C) and again in mid-February before bermudagrass emergence with 840 and 1,680 g ae ha-1 of glyphosate (Roundup Powermax) and 105 and 210 g ai ha-1 imazapic (Plateau). December application was equivalent to CDD of at least 460 using a base temperature of 22 °C and the formula CDD = 22 - [(Tmax+Tmin)/2]. Visual control of dallisgrass at 113/31 DAT was greatest (>90%) from either rate of glyphosate or imazapic during December and either rate of glyphosate during February. December application of glyphosate also resulted in the largest reduction (>67%) in dallisgrass occurrence by 166/84 DAT. In order to achieve the greatest amount of bermudagrass coverage during spring emergence, at least 840 g ae ha-1 glyphosate could be applied in December or February or 210 g ai ha-1 imazapic in December. This data indicates effective dallisgrass control and bermudagrass safety are achieved when herbicide applications are made above CDD = 460. It is suggested that field observations should accompany CDD measurements to ensure bermudagrass dormancy. February applications of imazapic were ineffective at reducing dallisgrass stand occurrence. 

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