It’s no secret that many almond and pistachio nut growers in California found much lower navel orangeworm (NOW) damage in their crops in 2019, but no one is guaranteeing that 2020 will bring a repeat of that good fortune.

Navel orangeworm populations in California’s pistachio and almond orchards can “turn on a dime” according to Joel Siegel, USDA-ARS research entomologist, without continuous attention to good control programs. Navel orangeworm damage in previous ‘bad’ years contributed not only to lower marketable yields, but also affected export opportunities.

A primary pest in almond and pistachio orchards, navel orangeworm is also prolific, producing three to four generations in one growing season. The larvae overwinter in mummy nuts left in the orchard after harvest. First instar larvae take advantage of hull vulnerability and early splits to bore into the kernels and feed. Larval feeding can also introduce fungal infections leading to aflatoxin contamination. In almonds some cultivars are more susceptible to damage, especially later-maturing softshell almonds with a lengthy hull split period or a poor shell seal. Early splits and pea splits in pistachios invite NOW infestations. Poor hull integrity also makes pistachio nuts vulnerable to NOW.

Though aflatoxin is a natural occurrence when growing almonds, and some variability in test results is expected. Managing the issue carefully is an important priority for the Almond Board of California, Julie Adams, the Almond Board’s Vice President of Global Technical and Regulatory Affairs, said at The Almond Conference 2018 in Sacramento.

Lower NOW damage in pistachio during the last two years was due to good hull integrity, Bob Klein, manager of California Pistachio Research Board said. Damage levels during the past two years are unprecedented in the industry and Klein warned growers not to expect a third year in 2020.

Good orchard sanitation is the cornerstone of NOW control, University of California farm advisors, and industry representatives strongly agree. Mating disruption is an effective tool as are timed insecticide sprays and early harvest.  However, Klein noted at the recent Pistachio Day event, that less than one in eight pistachio growers use all the tools available to them for NOW control.

“If 50 percent of growers are doing overwintering sanitation I would be surprised,” Klein said.

Almond and pistachio growers who cut back on NOW control efforts also put neighboring orchards at a higher risk of NOW infestation.

“At minimum look at your sanitation practices. They are the cornerstone of control – even if your damage is low,” Siegel said.

Siegel noted that in almonds, damage was not uniformly low up and down the Central Valley. North of Merced, NOW damage levels were higher, and aflatoxin was more of an issue. South of Merced, NOW levels never amplified in pistachio orchards over the season, he said, possibly because growers have taken orchard sanitation more seriously due to higher levels of NOW infestation in the past.

Besides orchard sanitation as a control, Siegel said growers would need a timely insecticide spray program. Mating disruption is not a stand-alone control, it needs insecticide support, Siegel said. Growers can decide if they want to eliminate one spray per season, but they need to understand that using all the NOW control tools available will help them achieve desired results.

Urged by their industries and buyers, more almond growers have performed orchard sanitation to reduce overwintering NOW populations and adopted mating disruption to protect developing nuts. Spray timing and techniques have also contributed to control efforts and cleaner nut crops.

A singular approach to NOW control is not effective, said UC IPM Extension advisor Emily Symmes. Without good orchard sanitation, numbers can be significantly reduced with mating disruption. If timing is not right or spray applications can’t be done within a short amount of time, populations will remain and build over the growing season, putting much more pressure on the crop at harvest.

Keeping an eye on the neighbors and their NOW control- or lack of- programs is also important, Siegel said. Navel orangeworm moths can fly in when one of their numerous host crops dries up or is harvested.

When infested trees of alternate hosts are harvested, navel orangeworm moths may migrate into almond orchards. Treating border rows (at least 10 rows) may be adequate to prevent the moths from infesting the almond crop when navel orangeworm numbers are low to moderate in a given area.

Constant vigilance in controlling NOW in almond orchards will keep reject levels down said Mel Machado, director of grower relations for Blue Diamond Growers.

The reason damage levels in almonds are down, Machado said is because more growers invested in sanitation. They should also be taking a serious look at mating disruption. Machado said use of this tool for NOW control would make hull split treatments more effective.

He said he is hearing from almond growers who have a good NOW control program that they have been able to cut one spray application- not eliminate altogether.

Zack Raven, ranch manager and grower services for Keenan Farms said securing export markets is vital for the pistachio industry. Lower prices for exported pistachio nuts or outright rejection of shipments due to aflatoxin contamination could be the outcome if pistachio growers are not vigilant every year in controlling NOW.

Considering the larger harvests that are on the horizon for the pistachio industry, Raven said taking orchard sanitation seriously is a must for all growers. If damage levels rise, customers are going to demand lower prices or not take the product at all.

When neighbors are on board with a control program, mating disruption is a NOW control tool that has proven to work. The plume of mating disruption pheromone expands and moves back and forth, he said, and has proven to be effective when coupled with orchard sanitation. Success with those two controls may allow a grower to skip a spray application after a year or two, he said.

Raven said depending on processor there is a potential to lose up to $0.20 per pound in quality bonuses due to insect damage, along with the damaged nuts in the load- which are not included in the grower’s total and not paid for.

Mating disruption cost ranges from $100-130 per acre. With an average size pistachio crop, it would only take about three cents per pound to cover the cost.

Raven said Keenan Farms is using one less spray due to our neighbors jumping on board with mating disruption and will continue to be vigilant with sanitation.

“Mating disruption has saved us $50 an acre and more importantly, helps secures our export markets for the future years to come,” Raven said.