Planning Your Weed Management Strategy for Orchards and Vineyards

The exact Critical Weed-free Period for bearing trees and vines is difficult to define, but it appears that controlling weeds from bud break until about 30 days after bloom will maximize your yields. So how can we accomplish this?

Fruit tree growers tend to take one of two approaches:

Apply a soil residual herbicide before weeds emerge in the spring, and plan to follow with a 2^nd treatment in about 8 weeks (early June).

Advantages:

• Maximizes yields by controlling weeds through the critical weed-free period.
• Frees up time for important bloom disease sprays.
• Removes overwintering weeds harbouring tarnished plant bugs.
• Allows pruning and early hand thinning to proceed.
• Allows late season weeds for beneficial insects.
• Works best for early harvested crops e.g. cherries, apricots, summer plums, early peaches.

Disadvantages:

• Need to apply very early - before weeds emerge. Difficult in an early year.
• May require a 3^rd treatment by early August to prevent harvest problems.
• May allow weed seedbank increase due to late summer escapes.
• The 2^nd treatment may be required before spring jobs are finished.

Allow early season weeds to grow for a couple of weeks, before applying a burndown treatment. May include a soil residual herbicide. Plan to follow with a 2^nd treatment in about 4-8 weeks (early July).

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Advantages:

• Flexible for time of application for 1^st treatment.
• Allows scouting to identify what weed species are present.
• Usually does not require a 3^rd treatment.
• Can avoid soil residual herbicides - safer for soils > 2% organic matter.
• Provides refugia for beneficial insects early in spring.
• Allows late season weeds for beneficial insects.

Disadvantages:

• May reduce yields by allowing weed competition during critical period.
• May not control winter annual weeds that have bolted at time of application.
• May allow build-up of tarnished plant bugs or other pests.
• 1^st treatment timing coincides with many other operations.
• Crop loads pull branches down when 2^nd treatment is required.

Grape growers will have similar options, but their season is pushed back by several weeks. However, the later harvest season for grapes may increase the need for late season weed control to enhance harvest operations. Grape growers need to assess the need for August treatments, depending on weed escapes. Growers who hill vines for winter protection will control early weeds when they begin to dehill, and will control late weeds when they start to build the hill in late summer. Hilling compresses the time to control weeds to about 8 weeks.

Planning the timing of the required 2 or 3 treatments, and integrating them into your other work plans, should ensure that weeds are in control during the Critical Weed-free Period and will not rob yields from your crops.

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