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Post-dormancy Growth of Bermudagrass as Influenced by Low Temperatures and Selected Preemergence Herbicides¹

Turf managers in the upper south of the USA must often contend with slow recovery of bermudagrass (Cynodon sp.) following winter dormancy. It is, therefore, essential to identify factors which may contribute to reduced. recovery from dormancy if bermudagrass is continued to be grown in this region. In this study, three experiments were conducted to determine the influence of the herbicides DCPA (dimethyl tetrachloroterephthalate), benefin (N-butyl-N-ethyl-,,-trifluoro-2,6 dinitro--toluidine) and oxadiazon [2-tert-butyl-4 (2,4-dichloro-5-isopropoxyphenyl) -²,3,4-oxadiazolin-5-one] on cold temperature tolerance and post-dormancy growth of three bermudagrass cultivars, ‘Tifway,’ ‘Vamont,’ and ‘Midiron.’

Two laboratory studies were designed to determine the influence of different rates of herbicides on the recovery of dormant bermudagrass that was subject to low temperatures. Herbicides were applied immediately before dormancy was initiated or prior to post-dormancy growth. A field acclimated study was also conducted to ascertain the effects of herbicide application on post-dormancy growth of two bermudagrass.

From these experiments it was found that the preemergence herbicides DCPA, benefin, and oxadiazon reduce the cold temperature tolerance of Tifway bermudagrass. Post-dormant root growth of Tifway bermudagrass was inhibited when new roots came into contact with a herbicide residue from an application prior to dormancy. The most severe root reduction occurred by applications of herbicides to dormant bermudagrass turf made after a laboratory freeze.

Less phytotoxicity was obtained when low dosages of herbicides were applied to dormant Vamont bermudagrass that was not frozen. However, when herbicides were applied after Vamont bermudagrass was frozen, both low and high dosages produced similar results.

Midiron and Vamont bermudagrass differed in their susceptibility to herbicide injury following freezing conditions. Vamont post-dormancy recovery was decreased by the herbicides applied in this study, but Midiron was not.

Key Words: Cynodon sp. • Freezing • Cold injury • Turfgrass

² Ph.D. candidate and research assistant, The Pennsylvania State Univ. and associate professor of agronomy, Virginia Polytechnic Institute and State University, respectively.

Received for publication August 14, 1980.