Effects of Metribuzin on Net Photosynthesis of Goosegrass (Eleusine indica) and Bermudagrass (Cynodonspp.)

Abstract

The influence of metribuzin [4-ammo-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] on net photosynthesis of goosegrass [Eleusine indica(L.) Gaertn. ♯3ELEIN] and six cultivars of bermudagrass [Cynodon dactylon(L.) Pers. ♯ CYNDA cvs. ‘Common’, ‘Tufcote’, ‘Vamont’, and ‘Midiron’,Cynodon transvaalensisDavy., andCynodon dactylonXCynodon transvaalensis‘Tifway’] was evaluated. Metribuzin rapidly inhibited carbon dioxide (CO2) uptake within 1 h after application in both goosegeass and bermudagrasses. Very often, net photosynthesis was completely inhibited. Net photosynthesis in goosegrass was inhibited by lower rates of metribuzin than those required for similar reduction in bermudagrasses. Common, Tufcote, Tifway, andC. transvaalensisbermudagrasses were less sensitive to metribuzin than Midiron and Vamont based upon the degree of inhibition of net photosynthesis, the rate of its recovery, and the level of foliar injury. Recovery from inhibition of net photosynthesis was observed in both species 24 h after treatment with low metribuzin rates. High rates caused several days lag period before net photosynthesis resumed. After 10 days, 95% of the goosegrass foliage was injured (either chlorosis or necrosis) from 2 kg ai/ha metribuzin treatment. The threshold concentration for inducing leaf injury in bermudagrasses was 1 kg ai/ha. Inhibition of photosynthesis was initially rapid in both grasses; however, recovery was evident earlier and there was less foliar injury in bermudagrasses than in goosegrass. Selective control of goosegrass in bermudagrass may therefore be partially dependent upon rapid metabolism and/or inactivation of metribuzin in the bermudagrass.