Hull split is approaching the the central San Joaquin Valley. In Kern COunty, hullsplit of almonds has been observed on the edges of blocks and tops of the trees, and will progress rapidly from this point forward. Hullsplit is a traditional time of making an application of insecticide to reduce navel orange worm damage and late season mite pressures. Blanks, or unpollinated or aborted fruit, will split first before the rest of the crop.
So, as a grower, what do we need to keep in mind during hull split?
1. Insect pest management, which includes Navel Orange Worm and Spider Mites.
2. Water Management to reduce the incidence of hull rot.
We will cover point 1 today, and the disease hull rot later this week.
1. Insect Pest Management practices for Hull split.
Spider Mites: A miticide will be necessary if a pyrethroid was used within the orchard. Pyrethroids target both spider mites and predator mite populations. Once the predator mites are reduced, the faster reproducing problematic spider mites can flare up, causing tree defoliation. It is essential to include a miticide tank mixed if spraying a pyrethroid. If not using a pyrethroid, scouting the trees can give you an idea if you need to include a miticide. Scouting for mites is simple, should be done in the morning when it is cool, and can give a good idea about the ratio of predator mites to spider mites in your orchard. Please refer to the University of California Integrated Pest Management page for information on how to scout for mites: UC IPM Scouting for Spider Mites.
There are several miticides to choose from at hull split. The most commonly used include Acramite, Envidor, Fujimite, Kanemite, Oil, Omite and Zeal. Each of these products can be effective, depending upon populations of spider mites present. The products need to be used before webspinning occurs. Webs that are spun within the leaves will repel the miticide, and will render it ineffective.
Navel Orange Worm:
Navel Orange Worm moths has been observed laying eggs on traps around the state, indicating that the next generation is about to begin. During this flight, eggs are laid on the suture and surface of the nut, and inside of a split-hull. The spray should be timed for the beginning of hull split if laid eggs are found on the egg traps. If eggs are not found on the traps at hull split, attempt to time the spray for the initiation of egg laying following hull split. Be aware that once hull split occurs, egg laying on traps will decrease. If you are not seeing eggs on traps, use degree-day information and apply a treatment at 1200 degree-days from spring biofix.
At hullsplit, a knockdown insecticide targeting navel orangeworm will reduce populations of adults, hatched larvae (worms), and eggs. Any in season use of a broad spectrum insecticide (AZINPHOSMETHYL(Guthion), CHLOROPYRIFOS (Lorsban), PHOSMET (Imidan), and ESFENVALERATE (Asana)) during this period or previously in the season to control navel orangeworm (or other insects) could possibly flare up spider mites, and thus a miticide should be included in the tank mix.
Use of softer, target specific chemicals (METHOXYFENOZIDE (Intrepid), SPINETORAM (Delegate), or SPINOSAD (Entrust or Success) will target navel orangeworm, and reduce the need for a miticide application. These insecticides are target specific, break down quickly in the environment, and lesser impacts on non-target organisms.
This season, it appears that the second twig borer flight will coincide with the flight of the navel orangeworm. This is good news as both pests will be targeted with a single spray!
More information on navel orangeworm and peach twig borer can be found at UC IPM Overview of Pests and Disease for Almonds
A link for Day Degree Hours from various locations around California from throughout the season can be found at Trece Field Reporter.
Let me know if you have any questions!