The trend in SJV orchards has been to eliminate the insecticide from dormant sprays and use only oil and a copper formulation. This is due in part to environmental concerns various levels of Lorsban and diazinon have been detected in streams and rivers by EPA and the desire to reduce costs. In most cases, such a program, when combined with spring Bt sprays has been successful. Some of the damage was due to leaf rollers but PTB almost always contributed to the rejects. Growers who had significant amounts of damage from PTB last year may need to return to a traditional full dormant spray program that includes both oil and an insecticide.
Growers can take precautions to avoid transport of pesticides from the orchard.
Avoiding spraying on foggy or breezy days will reduce airborne transport. If you are not going to apply a dormant insecticide you need to carefully asses what your risk is and monitor now and in the spring. This will be the primary source for spring infestations. Continue to monitor for strikes throughout the spring and summer and be prepared to treat the second summer brood if needed. Damage in prunes is not as common as in peaches.