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Selecting a Weed Management Strategy for Tree Fruit and Grapes

Early season weed control (bud break until 30 days after bloom) is the most important time to control weeds under fruit trees. It's not easy to find time to apply herbicides or cultivate during this time. Now is the time to plan the timing of these operations.

Fruit tree growers tend to take one of two approaches:

1. Apply a soil residual herbicide before weeds emerge in the spring. Plan to follow with a 2nd 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 eg. cherries, apricots, summer plums, early peaches.
  

  Disadvantages:
  

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

2. 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 2nd treatment in about 4-8 weeks (early July).

Advantages:

• Flexible for timing of 1st treatment.
  
• Allows scouting to identify weed species present.
  
• Usually does not require a 3rd 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 well.
  
• May allow build-up of Tarnished plant bugs or other pests.
  
• 1st treatment timing coincides with many other operations.
  
• Crop loads pull branches down when 2nd treatment is required.

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.

Weed Management Strategy for Grapes

Grape growers have similar options to those listed for tree fruit above, 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. This is another advantage of hilling - compressing the need for weed control to about 8 weeks.