Yaupon response to tebuthiuron and fire

Abstract

A study was initiated in April 1978 to examine the response of yaupon (Ilex vomitoria Ait.) to various rates of tebuthiuron {N-(5-1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl)-N,N'-dimethylurea} applied at various seasons, evaluate the influence of soil characteristics on tebuthiuron efficacy, examine yaupon susceptibility to fire, and evaluate the regrowth rate of yaupon following burning at various seasons. Tebuthiuron at 2 or 4 kg/ha significantly reduced yaupon canopy cover 2 years following application in the spring. Live stem densities of yaupon greater than 1.8 m tall were reduced 75% by 2 years following tebuthiuron applications of 2 or 4 kg/ha in the spring. Tebuthiuron applied at 2 kg/ha in the spring generally resulted in the same yaupon control as did 4 kg/ha applied at other seasons. Tebuthiuron phytotoxicity (% defoliation, % mortality) to huisache (Acacia farnesiana (L.) Willd.) and soil clay or organic matter content were inversely related. Tebuthiuron at 1 or 2 ppmw resulted in 100% mortality of huisache 287 days following application, regardless of clay or organic matter contents. However, tebuthiuron applied at 0.12 or 0.25 ppmw killed huisache only when applied to soils with less than 15% clay or 2.5% organic matter. A greater proportion of variation in tebuthiuron phytotoxicity to huisache was caused by the amount of variation in clay than by the amount of variation in organic matter content of the soils. ...