Tebuthiuron Formulation and Placement Effects on Response of Woody Plants and Soil Residue

Abstract

Tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea} in various formulations and placements was applied to honey mesquite (Prosopis glandulosaTorr. # PRCJG), huisache [Acacia farnesiana(L.) Willd. # ACAFA], live oak (Quercus virginianaMill.#QUEVI), Macartney rose (Rosa bracteataJ. C. Wendl. # ROSBC), and Texas whitebrush [Aloysia gratissima(Gillies & Hook.) Troncoso # ALYLY]. There was little difference in a species response to the various tebuthiuron formulations. Pellets (20%) at 2 g ai/tree base reduced the canopy 85% and killed 50% of the honey mesquite. At 1 g ai/plant, two briquettes at 0.5 g ai each or pellets (5.14 g, 20%) killed 37 and 80% of the huisache, respectively. Pellets were no more effective at 2 g than at 1 g ai on huisache. Basal treatments of 0.25, 0.5, 0.5, 1, and 2 g ai tebuthiuron/tree killed from 8 to 22, 48 to 62, 62 to 85, and 92% of the live oak, respectively. Pellets at 2 g ai placed at the base reduced the canopy 83% and killed 59% of the Macartney rose. On Texas whitebrush, 0.25, 0.5, 1, and 2 g ai tebuthiuron/tree killed from 68 to 85, 75 to 100, 90, and 100% of the plants, respectively. Tebuthiuron persisted mainly in the upper 30 cm of soil for at least 15 months.