Postemergence Weed Control In High Density Olive (Olea europaea L.) Production.

Field experiments were conducted at the Central Texas Olive Ranch in Walburg, TX in the summer of 2011 to evaluate the efficacy of postemergence herbicides for weed control in high density olive (Olea europaea L.) production. Studies were conducted on three year old olive trees grown on Houston Black (fine, smectitic, thermic Udic Haplusterts) soil. Plots measured 1.8 x 4.8 m and were arranged in a randomized complete block design with four replications of treatments. Each plot contained four olive trees spaced 1.2 m apart. Herbicide treatments were applied using a CO₂ backpack sprayer equipped with XR8003VS nozzle tips and calibrated to deliver 304 L/ha at 275 kPa. Treatments were initiated on 4/29/2011 and consisted of single or sequential applications of quinclorac (0.42 kg ai ha^-1), metsulfuron (0.042 kg ai ha^-1), thiencarbazone + iodosulfuron + dicamba (0.18 kg ai ha^-1), aminocyclopyrachlor (0.052 kg ai ha^-1), glyphosate (1.16 kg ai ha^-1), and mesotrione (0.21 kg ai ha^-1). Thiencarbazone + iodosulfuron + dicamba treatments were applied with a methylated seed oil at 0.5% v/v. Sequential treatments were applied four weeks after initial treatment (WAIT). A non-treated check was included for comparison purposes. O. europaea phytotoxicity ratings and % weed control were recorded 1, 2, 4, 5, and 8 WAIT. Data were subjected to analysis of variance and means were separated using Fisher’s Protected LSD (α = 0.05). No O. europaea phytotoxicity was observed throughout the length of the trial. Single applications of metsulfuron and glyphosate exhibited 35 and 37% weed control respectively, 4 WAIT. All other single application treatments exhibited ≤ 20% control 4 WAIT. Single applications of metsulfuron and aminocyclopyrachlor exhibited 55 and 31% weed control respectively, 8 WAIT. All other single application treatments exhibited ≤ 4% control 4 WAIT. Sequential applications of metsulfuron, mesotrione, and aminocyclopyrachlor exhibited 60, 47, and 46% weed control, respectively, 8 WAIT. All other sequential treatments exhibited ≤ 30% control 8 WAIT. Low humidity, high temperatures, and high winds may have contributed to reduced herbicide efficacy. This trial will be replicated over time.