Treating for Peach Leaf Curl and Peach Twig Borer from San Francisco to San jose and from Santa Cruz to Monterey:
Peach Twig Borer
This is an insect pest. The culprit is the larvae from a moth that lays her eggs on peach trees. The larvae hatch and bore into the stems and branches of trees causing damage and allowing pathogens to enter. The point of entry where the larvae overwinter is often near a pruning wound, crotch or deep bark fissure. There may be frass (sawdust) where the borer has made its entry. This frass is often washed off after first rains and therefore not a good telltale of infection later in the year. Larvae emerge in spring just before move up twigs to feed on new leaves & blossoms. Larvae mine the inside of new shoots causing dieback.
The best management of twig boer is well timed insecticides around bloom time. They can also be controlled by spraying in the dormant season to kill overwintering larvae. For organic control of beach twig borer, application of Bacillus thuringiensis spray, or Entrust formulation of spinosad, as well as some horticultural narrow range oils, can have good results.
Peach Leaf Curl
Peach leaf curl is caused by a fungus called Taphrina deformans. Peach leaf curl infects blossoms, fruit, leaves, and shoots of peaches and nectarines. Though this disease appears to be mainly cosmetic, severe infection can effect fruit production.
How Leaf Curl infects Peach and Nectarine Trees
Fungal spores survive the summer on the trees bark. With the onset of cool, moist weather the spores come out of dormancy get splashed onto new leaves in raindrops.
Peach leaf curl prevention:
Selecting resistant peach and nectarine varieties. Treat with a fungicide during dormant season. In a particularly wet winter, apply a second application of fungicide late in the dormant season, near bud-swell.
Pruning out diseased tissue is not an effective method for control.