As an incredible rainy season has allowed, orchard sanitation should be complete in most orchards, marking the beginning of the next chapter of insect management for California tree nut operations.
While some areas in the Sacramento Valley may still be in late bloom or petal drop, only days remain before warm weather begins to set in marking the return of more normal spring conditions. But the season for an influx of damaging insects is just ramping up.
Trap placement should have been set for Oriental fruit moth, and if weather has allowed, navel orangeworm (NOW) egg traps should be set out my mid-March in the San Joaquin Valley and by April 1 for more northern areas at a rate of about one trap per 10 acres. Almost no sanitation effort can eliminate all mummy nuts, and any remaining mummies are vulnerable to NOW females before new nuts are available.
Monitor traps twice a week for best results until a biofix is established. The biofix to start degree-day accumulation is established when egg numbers and number of traps with eggs increase for at least two consecutive sampling periods or when half of the traps have eggs.
Growers in the San Joaquin Valley are generally more at risk for the reintroduction of navel orangeworms for environmental reasons, even if cultural (sanitation) efforts were completed efficiently and on schedule, so the use of egg traps is especially helpful in determining NOW pressure in the weeks ahead as egg traps are valuable in estimating biofix and degree-day accumulation.
The placement of pheromone traps in the orchard is also an important tool in the control of male navel orangeworm, peach twig borer, and San Jose scale.
Hang pheromone traps for male navel orangeworms in tree canopies at approximately six to eight feet. Hang one trap for every 50 acres and at least two traps per orchard. Count the number of moths in the trap at least once per week and track the data to identify adult flight.
These traps are also useful in assessing whether mating disruption efforts are working properly.
Mid-March is also the right time to set traps for peach twig borer. Biofix in 2018 was near the end of March for some areas.
Additional information and recommended pheromone traps can be found at the University of California Statewide Integrated Pest Management Program’s resource page and for more information on recommended bait here.
According to UC-IPM, mating disruption is a relatively new technique for managing navel orangeworm in almonds. Disruption should be used as a supplemental management tool in conjunction with strategically applied insecticides and mostly in orchards with high numbers of navel orangeworm or in the first years of a mating disruption program.
Mating disruption dispensers should be hung from sturdy limbs midway up the tree in late March or early April according to manufacturer's guidance. In areas where the wind blows from one predominant direction, traps should be placed so there is a higher density of traps on the windward edge of the orchard.
In orchards with mating disruption, be aware that pheromone traps do not effectively monitor male flights.
Use pheromone traps to assure that suppression of mating is achieved. Pheromone-only traps in mating disruption blocks should usually capture no adults, and no more than a few weekly at most.
Use egg traps and monitoring of eggs on early-split nuts to determine the timing of insecticide treatments in orchards using mating disruption.
As a courtesy, consider informing your almond, walnut, and pistachio neighbors about mating disruption use in the area, as NOW pheromone monitoring trap catches may be affected in areas outside of the treated orchard.
Monitoring for other common winter/spring pests
March-May is also prime time for infiltration of spider mites into the orchard. Initially a bi-weekly scouting program is enough but that should increase to weekly scouting as summer approaches.
Early damage is indicated by lightly stippled leaves in the lower and interior portion of the canopy. Because of the difficulty of spotting spider mites, UCCE advisors recommend collecting about 15 leaves randomly from a number of trees in each acre and inspect them using a hand lens for easy detection. You should also be able to note spider mite predators using the same method.
Some tree nut orchards may wish to scout for overwintering leaffooted bug if they experienced pressure in previous years. These invasive insects also move into the orchard in March and April and can infest young nuts before shell hardening. While stink bug activity can begin in May, be careful not to confuse leaffooted bug with them as they can cause staining very similar to stink bug.
Scale pests (Walnut scale, frosted scale, European fruit lecanium)
Recent research has shown that there are two primary effective timing(s) for treating scale pests in walnuts: delayed-dormant and spring (crawler) timing.
Dormant observations are best for determining whether treatment is required, but for delayed-dormant timing, treat only if dormant monitoring indicates the need. This generally represents a stand-alone treatment. It is best to have this treatment complete before mid-April or the first week in May. This should be followed by spring crawler monitoring using double-sided sticky tape for walnut scale, visual observations of eggs/crawlers beneath frosted scale bodies.
Time treatment to the emergence of crawlers, typically one week after detection of the first crawlers. For walnut scale, look for the appearance of small, yellow, mite-sized crawlers to build up on the edges of sticky tapes. For frosted scale and European fruit lecanium, lift the adult female bodies and visually look for eggs.
For more information, follow more complete guidelines from UC-IPM.
Trap set timeline for common pests
San Jose Scale Feb 20-Mar 1
NOW males Mar 1-Mar 15
NOW eggs Mar 15–Apr 1
Oriental fruit moth Mar 15-Apr 1
Peach twig borer Mar 15-Mar 28
When it comes to late winter/early spring insect management, the above guidelines represent only a few of the more common concerns. For a complete list of pest management strategies, contact your local UC-IPM advisor.