Why is fruiting important in an IPM program?

nutlets beginning to swell

Nutlets beginning to swell.

Developing fruit panicle (cluster)

Developing fruit panicle (cluster).

Early split nuts

Early split nuts.

Fruit development generally occurs between mid-April and the start of shaking, but dates may vary according to region, variety, and weather. This is an important time to monitor irrigation practices, hull split, invertebrates, diseases and weeds.

Fruiting is also a time to take into account pesticide residue levels at the time of harvest before a treatment is made.


While it is important to avoid severe water stress during rapid shell growth in order to reduce the incidence of early shell split and thus navel orangeworm infestations, it is also important to adjust irrigation if Alternaria blight is serious so that the period from August 1 to 10 is irrigation-free.

Hull splitting

It is important to look for "early splits". Typically the internal pistachio shell splits before harvest while the protective outer hull stays intact until after harvest. Early split nuts are when both the outer hull and internal shell split while still on the tree, exposing the kernel to invasion by insects and molds, including Aspergillus flavus which produces aflatoxins.

To make navel orangeworm treatment decisions, consider early splits, historic navel orangeworm problems, the abundance of old "mummy" nuts, the projected harvest date, and the presence and condition of surrounding orchards, especially almonds. More than 2 early splits per 100 nuts signals potential problems from navel orangeworm and treatment is recommended. If harvest is planned for mid-September to October, a second application will be needed.

Invertebrates monitoring

Citrus flat mite, navel orangeworm, leaffooted plant bugs, and stink bugs are key pests at this time. If unchecked, increasing citrus flat mite populations can arrest fruit development and growth. Navel orangeworm infests the nut meat and leaffooted bugs and stink bugs can transmit stigmatomycosis under moist conditions.

  • Navel orangeworm
    Check egg traps to identify the first and second generations; use degree-days and egg trap monitoring to identify the treatment timing, which is at the beginning of the third generation.
  • Obliquebanded leafroller
    Hang pheromone traps by late April in Kern and King counties, or April 25 in Fresno and northward. Note biofix (the first date when male moths are consistently caught in traps). Continue monitoring traps to determine treatment timing.
  • Bugs
    Use a beating tray to monitor clusters for nymphs of small plant bugs, stink bugs, and leaffooted plant bugs; cut open black nuts to confirm if there is bug feeding; check for stink bug and leaffooted bug eggs on leaves or fruit; sample for Calocoris norvegicus and lygus bugs with a sweep net in ground cover and weeds.
  • Mealybugs
    Check trees where mealybug infestations were noted after harvest or at budbreak.

Disease monitoring

Weed monitoring

Statewide IPM Program, Agriculture and Natural Resources, University of California
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