An evaluation of 1, 8-naphtholic anhydride as a chemical antidote to prevent alacholar injury to grain sorghum

A study was conducted to determine: (1) the tolerance of grain sorghum to 2-chloro-2', 6'-diethyl-N-(methoxymethyl) acetanilide (alachlor) applied at rates commonly used for weed control, (2) the effectiveness of 1,8-naphthalic anhydride (hereafter referred to as anhydride) seed treatment in protecting grain sorghum from alachlor injury, and (3) the differential response of various grain sorghum (Sorghum bicolor (L.) Moench.) cultivars to alachlor and anhydride. In a greenhouse experiment, the effects of four anhydride rates and five alachlor rates on grain sorghum cultivar AKS 614 were studied. The effects measured were percent vigor reduction, percent emergence, height, and dry weight of seedlings. Anhydride protected grain sorghum from severe alachlor injury; however, rates above 0.5% w/w did not provide significant additional protection. The lowest rate of alachlor (2.24 kg/ha) resulted in a sig-nificant decrease in each measurement from the untreated control and there was a trend for further reduction as the alachlor rate was increased to 3.36 and 4.48 kg/ha. The effects of anhydride at two rates and alachlor at four rates on three grain sorghum cultivars (AKS 614, BR 64, and McNair 546) were studied in an experiment conducted at the Plant Science Farm, Knoxville, Tennessee during 1971. The parameters measured were percent vigor reduction, plant population, plant height, whole plant weight, whole panicle weight, and seed yield. The plant vigor of grain sorghum cultivar BR 64, without an anhydride seed treatment was reduced more severely than cultivars AKS 614 and McNair 546. Anhydride seed treatment protected all three cul-tivars from alachlor injury to some extent; however, the injury grad-ually became worse as the alachlor rate increased. Without anhydride, there was a trend for the plant population, whole plant weight, whole panicle weight, and seed yield of cultivar BR 64 to be lower than those of cultivars AKS 614 and McNair 546. Cultivar McNair 546 was shorter than the other two cultivars at all alachlor rates regardless of anhydride seed treatment. This height dif-ferential was probably due to the genetic differences between the cultivars. The anhydride seed treatment protected all three grain sorghum cultivars from severe alachlor injury. Cultivars AKS 614 and McNair 546 appeared to be more promising for commercial use than cul-tivar BR 64.