Submitted to: Applied Turfgrass Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/13/2010
Publication Date: 2/22/2011
Citation: Umeda, K., Shaner, D.L. 2011. How Rapidly Do Fall-Applied Prodiamine And Dithiopyr Disperse In Established Bermudagrass Turf In Arizona? Applied Turfgrass Science. DOI:1094/ATS-2011-0207-01-RS. Interpretive Summary: Annual bluegrass is a major turf weed. Prodiamine and dithiopyr are pre-emergent herbicides that are used to control annual bluegrass in turf. In Arizona, these herbicides are applied in late August to control annual bluegrass but to also allow time for the herbicides to dissipate before overseeding with perennial ryegrass. In this study we compared the rate of dissipation of prodiamine and dithiopyr and found that dithiopyr dissipated almost twice as rapidly as prodiamine. The results indicate that prodiamine should be applied earlier in the year to allow more of the herbicide to be degraded before overseeding with perennial ryegrass whereas areas treated with dithiopyr should be overseeded sooner to allow the perennial ryegrass to outcompete the annual bluegrass.
Technical Abstract: Annual bluegrass is a major weed in turf. In Arizona, prodiamine and dithiopyr are applied in late August to provide pre-emergent control of annual bluegrass and to allow the herbicides to dissipate enough to allow overseeding with perennial ryegrass in October. This study was done to compare the rates of dissipation of prodiamine and dithiopyr in Bermuda grass turf from the time of application until overseeding at two different sites in Arizona. Neither herbicide leached out of the turf/thatch layer throughout the time course of the experiment. Dithiopyr dissipated approximately twice as rapidly as prodiamine at both sites. At the time of overseeding 30-40% of the prodiamine remained in the turf whereas only 12-16% of the dithiopyr remained. This resulted in some injury to the overseeded perennial ryegrass in the prodiamine treated areas and the loss of annual bluegrass control in the dithiopyr treated areas the following spring. These results suggest that prodiamine should be applied earlier in the year to allow time for the herbicide to dissipate before overseeding while dithiopyr treated areas should be overseeded earlier to allow the perennial ryegrass to outcompete annual bluegrass seedlings.