Weed Management Considerations When Replanting Trees in an Established Orchard
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.
|Preemergent Herbicides Registered in California for Prunes |
|Active Ingredient (Trade Name) ||Label Restrictions ||WSSA MOA2 |
|flumioxazin (Chateau) ||Do not apply to trees established less than one year. ||14 |
|indaziflam (Alion) ||Herbicide can ONLY be applied to established trees, minimum of three years after transplant, exhibiting normal growth and good vigor. ||29 |
|isoxaben (Trellis) ||Do not apply to newly transplanted trees until soil has been settled by packing and irrigation or rainfall with no cracks present. ||21 |
|mesotrion (Broadworks) ||Applications can ONLY be made to trees that have been established for one full growing season and are in good health and vigor. ||27 |
|norflurazon (Solicam) ||Applications can ONLY be made 18 Months after planting OR replacement of tree. ||12 |
|oryzalin (Surflan) ||Can be used on new transplants. Exposure of transplant roots to treated soil should be minimized to avoid any possibility of crop injury. ||3 |
|oxyfluorfen (Goal, GoalTender) ||May be applied to transplanted trees as a single or split application once soil has settled. ||14 |
|pendimethalin (Prowl H2O) ||Do not apply to newly transplanted trees until ground has settled and no cracks are present. ||3 |
|penoxsulam/oxyfluorfen (Pindar GT) ||Do not apply Pindar GT to bearing and non-bearing stone fruit trees that have been established less than 4 years. Apply only to tree crops in good health and vigor. Use trunk guards to protect plants until adequate bark has developed. ||2 |
|pronamide (Kerb) ||Do not apply to fall transplanted stock when transplanted less than 1 year or to spring transplanted stock when transplanted less than 6 months. ||3 |
|rimsulfuron (Matrix) ||Apply only to trees that have been established for one full growing season. ||2 |
|trifluralin (Treflan) ||May be applied to transplanted trees once soil has settled and trees are in good health and vigor. ||3 |
|1) Registration status as of January 2019 |
|2) Weed Science Society of America mechanism of action (MOA). It is critical to use herbicide MOAs in rotation or in sequence to minimize/delay development of herbicide resistance. ||2Weed Science Society of America mechanism of action (MOA). It is critical to use herbicide MOAs in rotation or in sequence to minimize/delay development of herbicide resistance. ||2Weed Science Society of America mechanism of action (MOA). It is critical to use herbicide MOAs in rotation or in sequence to minimize/delay development of herbicide resistance. |
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