California Prunes: Fall Orchard Management Considerations

Pruning Cautions:

  • It is critical to avoid timing pruning activities near rainfall events, whereby rain-splash can result in costly disease spread to freshly cut branches (see article in this newsletter).
  • In addition to avoiding new infections, it is important to prune out existing Cytospora cankers by cutting several inches to a foot into the healthy wood below any symptoms. The pruned out wood should be removed from the orchard and burned (if permitted).

Nutrition:

  • Potassium is the most critical nutrient in prune production and a band application in late fall can be
    one way to correct any deficiency and replace the potassium removed by the previous year’s crop.
  • Foliar zinc (36% zinc sulfate) can be applied at the beginning of leaf drop in late October or early
    November at about 20 lbs/acre in 100 gal water/acre. Zinc may drop leaves and disrupts aphid
    reproduction.
  • Once leaves drop, trees don’t absorb nitrogen until bud break in the spring. Any nitrogen applied in
    the fall won’t be in the root zone come spring, especially if we have a wet winter. Put another
    way,do not apply nitrogen until after growth begins next spring.

Aphid and Scale Control:

  • Aphids can be controlled with low rates of pyrethroid (Asana, etc.) or organo-phosphate (diazinon, etc.) pesticides when applied in November (pyrethroids) or December through February (organophosphates.). The proactive November timing is chosen when orchard history indicates a chronic problem, whereas later sprays should be warranted by the presence of any aphid eggs in the dormant spur sampling.
  • The dormant spur sampling conducted once between mid-November and mid-January, monitors for aphid eggs (only if not controlled in November), San Jose scale, European fruit lecanium and mites. Clip off 2-3 spurs from 35 to 50 randomly selected trees (for 100 total spurs) in each orchard and then carefully examine 20 random spurs with a hand lens or dissecting microscope, recording the number of spurs with any scales or aphid/mite eggs.

Weed management:

  • Following your postharvest weed survey (ipm.ucdavis.edu/PMG/C606/prune-fallweeds.pdf), apply
    mid to late fall preemergence herbicide applications shortly before rainfall events that move the
    material into the soil. Include a postemergence herbicide if rains have already stimulated weed
    growth. See article on weed management in prunes in this newsletter.



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