May Spray

(originally published June 2017)

As almond growers prepare for hullsplit sprays, it is time to review best practices for the most effective treatment program that follows an IPM approach and resistance management for treating navel orangeworm (NOW) and spider mites.

David Haviland, UC Cooperative Extension entomologist in Kern County, said this approach includes monitoring to determine navel orangeworm treatment timing, monitoring of mites and natural enemies to determine the need for a miticide, using selective chemistries, and rotating among pesticide modes of action to minimize pesticide resistance.

Navel Orangeworm

Cultural practices are the first line of defense against NOW. Prompt harvest and pickup, followed by removal and destruction of mummy nuts, is an essential first step in controlling NOW; hullsplit sprays are generally only about 50% effective because larvae are protected once they enter the hull to feed. Growers may have gotten a boost in their cultural control this year following unprecedented moisture through spring.

Nearly all growers spray for NOW at hullsplit, and many spray a second application two or three weeks later, according to Haviland. The most common insecticides used for NOW include the three chemical classes: pyrethroids, such as Brigade, Warrior II, etc.; insect growth regulators, including Intrepid; and the diamides, such as Altacor.

Although efficacy is similar among the three groups, pyrethroid efficacy is slipping, and their use causes other concerns, said Haviland during a presentation at The Almond Conference last December. Almond Board of California (ABC)–funded research has documented decreased efficacy as a result of increased levels of NOW resistance.

“Pyrethroids are broad-spectrum insecticides that are also effective against leaffooted bug and stinkbug, but they also reduce biocontrol of spider mites and scale by eliminating beneficials,” he explained, cautioning that there are also concerns about off-site movement of pyrethroids into waterways.

Whether resistance to pyrethroids is present or not in a particular area, the potential is there, and growers are cautioned to practice resistance management by using pyrethroids prudently and by rotating chemistries.

“So while pyrethroids may still be effective, they are not as effective as when they were first released,” Haviland noted. “A second concern for pyrethroids is their impact on beneficials, including those that prey on spider mites. Because of this, application of pyrethroids can lead to mite flare-ups; therefore, they should not be applied prior to hullsplit.” In addition, because of resistance potential, pyrethroids should only be used once during the season at this ‘best fit’ hullsplit timing.

In areas with moderate or high pressure or a history of NOW damage, a second application is made two or three weeks later, when Nonpareil nuts are completely split, pollinators are beginning to split, and residues from first sprays are beginning to degrade. If making more than one spray, be sure to rotate among chemical classes.

Mating Disruption


Another management technique Haviland discussed at The Almond Conference is mating disruption, in which the NOW pheromone is dispensed in the orchard as an aerosol. The pheromone acts by confusing males and inhibiting their ability to find females. The bigger the area treated with the pheromone the better, but research shows a benefit in plots as small as 20 acres.

Mating disruption can be used as either a stand-alone management tool, especially in sensitive areas such as nearby schools or along roadways, or in addition to spray programs under high-pressure conditions. Typically, they provide about 50% reduction in damage. This year, mating disruption programs are available from Suterra, Semios and Pacific Biocontrol.

Before implementing a management program at hullsplit, Haviland urged growers to use all tools available to monitor for NOW to determine the number of treatments and treatment timing. Intrepid and Altacor should be used as the primary insecticides, with pyrethroids used “judiciously.”

Spider Mites

Web-spinning spider mites are a concern during the summer and throughout harvest. The hullsplit spray for NOW provides a cost-effective opportunity to apply a miticide if it is needed. Haviland said decisions about tank-mixing miticides with hullsplit sprays should be based on sampling for mites and their natural predators.

In many cases, there are sufficient natural enemies present in the orchard to provide excellent late-season mite control. In other cases, he pointed out, it may be necessary to apply a miticide in a tank mix with a first or second hullsplit spray.

A View from the North


Also presenting at The Almond Conference, Dr. Frank Zalom, entomology professor at UC Davis, provided a history of NOW in almonds. “Navel orangeworm became the key pest of almonds in the late 1960s,” he said, “with some Sacramento Valley growers harvesting loads that reached 30% NOW damage in the late 1970s and average industrywide damage reached 8.8% in 1978.” This number dropped to an average of 1.5% from 1998–2000 following implementation of the Four-Point Program for NOW control, which was developed by Almond Board of California’s Bob Curtis and first published in 1978. Today, NOW damage has dropped to an average of 1% or less.

The Four-Point Program includes:

  • • Winter sanitation
  • • Dormant spray for peach twig borer (PTB) control
  • • Hullsplit spray
  • • Timely harvest

“These are still the most important management practices for the key insects [navel orangeworm and peach twig borer,] and mites in the northern San Joaquin and Sacramento Valleys,” Dr. Zalom stated, adding that dormant sprays are an exception because of concerns about storm water runoff and potential effects on pollinators, depending on products used and their timing.

Peach Twig Borer


Because managing PTB is important to prevent damage to nuts that make them more attractive to NOW infestation, Zalom suggested these alternatives for dormant sprays:

  • An earlier treatment timing, in November or December, before winter rains commence;
  • Use of alternative bee-safe products, such as B.t., in bloom sprays; and
  • Switching to a spring (“May”) spray.

A spring spray timed according to PTB captures in pheromone traps and degree days provides some control of NOW as well. Altacor and Delegate are effective against both insects. Intrepid is effective for NOW, but less effective against PTB.

Do not include a miticide in the spring spray unless sampling shows it is necessary, and do not use pyrethroid insecticides in spring sprays and it is best to avoid them in  hullsplit sprays, Dr. Zalom warned, as this may lead to spider mite outbreaks.

Finally, remember that managing NOW does not end for the season after hullsplit; a timely harvest and rapid pickup of nuts are essential for protecting next year’s crop.


A spring spray timed for peach twig borer also provides some control of navel orangeworm.