D. HAWTON

Abstract

Seed yields from herbicide screening experiments confirmed that atrazine selectively controls many weeds in Panicum maximum cv. Gatton (Gatton panic) and Brachiaria decumbens cv. Basilisk (signal grass) better than the other chemicals tested. A range of atrazine rates indicated that 2.2 kg ai ha^-1 was optimum for Gatton panic while 3 kg ai ha^-1 gave best results with signal grass. All rates of atrazine tested (from 1 to 5 kg ai ha^-1) reduced the population of Gatton panic. Atrazine at 1.25 and 2.5 kg ai ha^-1 did not significantly reduce the population of signal grass, but a significant reduction in population occurred when atrazine was applied at 5 kg ai ha^-1. Under dry, cool conditions when germination of Gatton panic was reduced, atrazine treated plots yielded less than handweeded but more than untreated plots. Signal grass yields were not reduced when atrazine was used under these conditions.