California almond growers will need a new paradigm in managing Navel orangeworm (NOW) as the destructive pest population continues to increase amid climate conditions that favor the pest.

Mel Machado, member relations director with Blue Diamond Growers, says almond reject levels doubled on average across the cooperative's grower members. Still, those averages hide the real story, he says.

“There were growers who hadn’t seen 2 percent (rejects) in many years that were in the 8-12 percent range and these are good growers,” Machado says.

For growers who don’t know by now, the Navel orangeworm feeds on a variety of fruits and nuts and is the most damaging caterpillar in pistachios, according to the University of California Statewide Integrated Pest Management Program.

Almonds, walnuts, figs and pomegranates are also major hosts. Combined there are over two million acres of NOW habitat in California with a near contiguous band of tree nuts stretching from Red Bluff to Arvin, a distance 400-plus miles. Moreover, the changing climate and generally warmer nighttime temperatures have allowed the pest to increase reproduction and add a generation at a time of year when nut harvest is in full swing.

Machado is getting the word out to Blue Diamond growers about the real economic impacts of NOW – especially for those who think that another chemical treatment might be too costly.

At a recent grower meeting in Modesto, Machado explained losses in a Nonpareil crop making 2,500 pounds per acre at $2.50 per pound. On 10 percent losses, this equals a $1,700 per acre loss in grower revenue.

In some cases, Machado says almond farmers saw 30 percent reject levels.

During the grower meeting, Machado shared several videos - including an almond stockpile where barn swallows fed feed on moths and worms in the almonds. He’s never seen this before.

In another example, a video from a Blue Diamond member showed a bug zapper at a well with numerous moths in the lights of thew spray rig during a nighttime application. The bug zapper filled up with NOW moths during a single night.

Michael Kelley, chief executive officer of the Central California Almond Growers Association at Kerman, said he had seen similarly high levels of NOW damage in his hulling and shelling operation this last summer.

Research

Dr. Joel Siegel, research entomologist with the USDA Agriculture Research Service, said warm summer night temperatures across California had helped generate another generation of NOW.  He said growers should ignore previous seasons where one chemical spray was necessary, and cautioned growers that anything less than sterling field sanitation – eliminating all mummy nuts during the dormant season – just won’t cut it.

The entomologist says growers should be aggressive in NOW orchard treatments as eggs laid in new crop Nonpareil almonds require 700 degree days to cycle and just 500 degree days in new crop pistachios. This compares to about 1,100 degree days to cycle in mummy nuts.

Siegel data suggests that degree days have increased by about 700 in the past few years leading to the additional generation.

Growers are encouraged to shake trees at dormancy and eliminate all mummy nuts by late year. These nuts can be destroyed by sweeping the mummies into windrows and shredding into mulch that's incorporated into the soil. Machado says growers should be meticulous in ensuring that mummy nuts don’t remain in the crook of the trees, a practice one of his better growers employs with good success.

Siegel believes an excellent winter sanitation program can eliminate the need for up to four sprays during the season. As for the spray timing, Siegel was blunt with the growers in the room.

“Listen to and heed your PCAs,” Siegel said at the Blue Diamond meeting. “You’re paying them for advice - use it.”

Common issues Siegel saw in 2017 included growers with little to no winter sanitation and thought they could get away with one NOW spray. In many cases, growers were prohibited from returning to their orchards to shake in December as heavy rains kept them out of orchards.

Siegel also saw growers who after being told by their PCA to spray on July 1 waited another week, only to completely miss effective spray timings that caused the NOW population to explode.

Perhaps another factor Siegel says to consider is the synergistic impact between mating disruption used to control NOW and adult traps. A grower using mating disruption can completely cancel any impacts his neighbor is having on traps, leading the grower to the false conclusion that there are no NOWs in their orchard due to zero trap finds.

Also at the Modesto meeting was Matt Strmiska, chief executive officer and co-founder of the company Adaptive. He is studying sprayer technology to determine if ways exist to put more chemicals on the target when making insecticide applications.

Strmiska and Siegel have collaborated on studies which suggest that current sprayer technologies are not effective in placing chemical treatments where necessary to achieve effective control. Several of Strmiska’s recommendations include:

Machado encourages growers to work together on pest control across their orchard blocks.

Blue Diamond will hold more grower meetings through the winter months to emphasis the need for winter sanitation, plus other effective tools to control NOW in almonds.