The pistachio tree appears to be very well adapted to our weather conditions in the San Joaquin Valley. The tree normally blooms after all danger of frost is passed, so in the past, unlike the almonds, peaches, apples, and other stone fruits, pistachios were not affected by late season freezes. However, if the trees are sprayed by winter oil, pistachio trees may bloom into freezing temperatures . One grower in the northern rolling-hill country of Kern County, lost 40 acres of production in the swales of a large orchard due to an early April freeze in combination with the early blooming trees. If the grower does not have his or her own harvest equipment, the early bloom and earlier harvest can present an additional problem.
Many growers are dependent on the prune shakers for harvesting their crop.
If the prune harvest is running late, and their nuts are ready earlier than usual as a result of the oil spray, increased navel orangeworm damage, sticking hulls, and stained nuts may be significant problems. Early evidence suggests that continual oil spraying may delay the down cycle of alternate bearing for up to three years, but an off year, when it returns, may be very off indeed. The following section is reprinted from an earlier newsletter. I have made additions and other changes in response to communication with growers, chemical representatives and others. This list is intended as a general guide only.