Evaluation of Mulch and Preemergence Herbicides for 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 spring and summer of 2011 to evaluate the efficacy of mulch and/or preemergence 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 4/1/2011 and consisted of isoxaben (2.2 kg ai ha^-1), oryzalin (4.5 kg ai ha^-1), oxadiazon (3.36 kg ai ha^-1), and mesotrione (0.14 kg ai ha^-1). Plots were irrigated following herbicide application with approximately 0.6 cm of water to ensure activation of herbicides in the soil profile. Hardwood mulch (to a depth of 6 cm) was applied to half of each plot immediately following irrigation.  A non-treated check was included for comparison purposes. O. europaea phytotoxicity ratings and percent weed control were recorded 1, 2, 4, 8, and 12 weeks after treatment (WAT). Data were subjected to analysis of variance and means were separated using Fisher’s Protected LSD at the 0.05 significance level. No O. europaea phytotoxicity was observed throughout the length of the trial. All preemergence herbicides exhibited ≥ 90% weed control 4 WAT. Mulch alone provided 72% weed control 4 WAT, however, preemergence herbicide efficacy was not enhanced by the addition of mulch. A similar trend was observed 2 months later. All preemergence herbicides exhibited 87 to 97% weed control 12 WAT. Weed control with mulch alone decreased to 50% 12 WAT, while preemergence herbicide efficacy was not enhanced by the addition of mulch. This trial will be replicated over time.