What can be done to avoid oil burn in prunes during 2009?

Young “red” wood or shoots are most sensitive to damage from dormant oil sprays. Oil burn can severely damage prune trees and can kill young prune trees in extreme cases. Exactly how oil damages wood in dormant prunes is not clearly known.

1) Use no oil or a very low oil rate of oil. Oil is not needed for excellent aphid or peach twig borer control. Oil is a very important material for scale control — with or without synthetic pesticide such as diazinon, Lorsban, Seize WP, etc.. Take a dormant spur sample to find out if you have a scale problem. Many prune blocks will not need scale control.

2) Wait until just before bloom to spray for dormant pests. The closer to bloom, the smaller the chance of oil burn.

Delayed dormant is a much safer timing than dormant for using oil in prunes. Note: Certain pesticides are very toxic to bees. If spraying pesticides just prior to prune bloom, make sure to follow all guidelines to protect bee health. Contact your local County Ag Commissioner’s office to determine local bee safety regulations. No bees = no prunes.

3) Irrigate your orchard before spraying. Dry soil is very strongly related to oil damage in prunes.

4) Wait until tree bark is moist (wet conditions). I have seen significant oil damage when trees on wet ground are sprayed on the first calm day after several days of dry north winds. Once rain or fog rewets trees, the risk of oil damage is greatly reduced. Be sure you understand what can lead to oil damage and know what conditions are like in your field.

Don’t take chances. Oil can damage or kill several years of growth.