Drew Wolter, UCCE Junior Specialist Horticulture Intern & M.S Student, University of California, Davis, Department of Weed Science
Weeds impact orchard productivity and health by competing with young trees for water, light, and nutrients, and may act as hosts for a variety of pests. The primary objective of a successful weed management program is to optimize tree growth, health, and/or yield by minimizing the impact of weeds. Preemergent (PRE) herbicides can be an effective tool in orchard weed management. When a PRE is properly selected, timed and applied, weed pressure can be significantly reduced during the onset of each growing season.
If you decide to replant into a mature orchard, you must be extremely cautious with your preemergent (PRE) herbicide applications. Carefully read the label before applying PRE applications near newly planted trees and to the surrounding orchard. There are currently twelve preemergent herbicides registered in California for use in prunes. All of the labels list replant restrictions (listed below) ranging from 30 days to 4 years from replant, along with guidelines to avoid phytotoxicity to young trees.
The residual weed control following PRE herbicide applications are affected by herbicide selection, application rate, soil texture, organic matter, and environmental conditions. If active PRE herbicides come in contact with young tree roots, significant injury can occur. Avoid backfilling planting holes with previously treated soil. Ensure the soil has completely settled before applying PRE herbicides if large cracks and holes are present in unsettled soil.