Mating disruption for navel orangeworm (NOW) has been widely tested throughout California with numerous research studies, and peer-reviewed research has demonstrated its efficacy.

Mating disruption is a very simple process. Females emit pheromones, males use those pheromones to find the female. If an orchard is flooded with artificially produced pheromone the entire orchard smells like a female and the males struggle to find the real females. If they don’t find each other, they don’t mate, and if they don’t mate there are no eggs, no larvae, and less overall nut damage.

Mating Disruption in Almonds and Pistachios

Navel orangeworm is a major and costly pest of almonds and pistachios for growers and processors.

Currently, growers use winter sanitation and chemical sprays for control, but mating disruption is another important tool at their disposal.

How mating disruption works is dispensers contain an artificial pheromone. They are placed in the orchard and inundate the orchard with the female pheromone so that the males either can’t find or are delayed in finding the females.

There are two types of dispensers for NOW. “Three companies have dispensers that use pheromone in aerosol cans,” according to David Haviland, University of California Cooperative Extension  (UCCE) entomology and pest management farm advisor in Kern County.

“Those dispensers are displaced at a rate of one to two per acre depending on the product, and the dispensers spray pheromone at preplanned intervals when the moths are active,” Haviland said.

With the fourth product, the pheromone is impregnated into a plastic strip. They are hung at a rate of approximately 20 per acre, Haviland said, adding this is the only dispenser that is approved for organic use, and it offers organic growers an option for mating disruption.

The other products are not organically approved due to the solvents involved in their production, Haviland continued.

“The solvents that are used to put the pheromone in those aerosol cans are not currently approved for organic use. The pheromone itself is organic, but the solvents are not,” Haviland said, adding efforts are underway to find organically-approved solvents that would allow for organic approval for a pressurized pheromone dispenser.

Placement

“All four products contain the same pheromone and contain approximately very close to the same amount of pheromone on a per acre basis over the season,” Haviland said.

Dispensers are typically placed in the orchard prior to the first NOW flight—typically by the end of March.

“For the three aerosol based products, the dispensers are installed towards the end of March-beginning of April and are removed at the end of the season and new ones are put in the next season,” Haviland said, adding all products last one season.

Installation of the passive dispensers is a very simple process that is also done around the end of March. Passive dispensers do not need to be removed at the end of the season.

Research

Haviland has done evaluations of all the dispensers in almonds and pistachios.

“We used 40 acre replicated trials to evaluate all four of these products. Data showed that all four can be effective. On average, they reduced damage by approximately 50 percent,” Haviland said.

That was followed with a larger scale, two-year trial with six side-by-side demonstration projects in the San Joaquin Valley that also showed a 50-70 percent reduction in damage using mating disruption for navel orangeworm.

All of the trials except for one were done using mating disruption in conjunction with existing sanitation and spray programs. In the final trial, mating disruption was used instead of insecticides.

“We’re not typically using mating disruption to replace sanitation or insecticides at this point. It’s another tool in the toolbox being used in addition to other tools,” Haviland said, noting that replacing insecticides is a possibility for orchards that have excellent sanitation and historically low levels of damage.

“One concern is that some growers want to pay for mating disruption by saving money on sanitation. Unfortunately, growers who don’t sanitize and expect that mating disruption by itself is going to solve the problem are setting themselves up for problems. However, research has shown that using mating disruption in addition to existing management programs, including sanitation and insecticides, is effective and can reduce damage by another 50 percent,” Haviland said.

Chemical Options

With the almond industry’s drive towards increased sustainability and no new insecticides coming down the pike for navel orangeworm, mating disruption is the choice, Haviland said.

“So it’s not just a matter of looking to see if mating disruption can work. It’s an active, progressive, research program to try and figure out how to make mating disruption work, and how to make it work as good as it possibly can,” Haviland said.

There is also the potential that mating disruption can result in less chemical applications between hull split and harvest, Haviland said.

“At this point, as a general recommendation across the state, unless you’re in that category of naturally low pressure, we don’t recommend backing off on your existing program when using mating disruption,” Haviland said, noting that finding ways to use mating disruption to reduce insecticide sprays is an area of active research for the future.

Future Research

Two of the three phases to Haviland’s research have been completed.

• • Phase one—show mating disruption works.
• • Phase two—does mating disruption consistently work and work well enough to justify its use.
• • Phase three—is mating disruption working well enough that it can start to replace existing programs including pesticides.

Phase one and two are proven. Phase three, we’re just not quite there yet, Haviland said.

Haviland will continue conducting mating disruption research to further refine ways to use mating disruption as well as additional methods for application.

Most of the research at this point has been in almonds, but there was scaled down research done in pistachios.

“We did get the same level of trap shutdown in pistachios that we do in almonds on navel orangeworm, however, this year there was no damage in pistachios by navel orangeworm,” Haviland said.

Because there was such low damage in pistachios in 2018 good harvest data wasn’t available in those trials, Haviland said.

Haviland plans to do significant mating disruption research on almonds in the future.

“It’s not just that we’re going to do research on mating disruption in the future, it’s that mating disruption is becoming a significant part of the future,” Haviland said.

Walnuts and Mating Disruption

Walnut growers have a more complex challenge when it comes to mating disruption. They face not only NOW but also codling moth (CM), and their harvest nut grade is based on the “worm damage” combined of these two pests.

NOW attacks the new nut crop primarily in the preharvest period at husk-split. CM larvae penetrate the walnut shell and eat the nutmeat throughout the growing season. NOW finds these nuts attacked by CM and enters the damaged nut through the exit hole provided by the CM larvae.

A single CM larvae will feed on the walnut consuming only a portion of the nutmeat. Once a NOW female finds a CM-penetrated nut it will lay multiple eggs, resulting in as many as a dozen worms that enter the shell and devour the remaining nutmeat.

NOW populations will rapidly build up in the mid-season period, then emerge in August and attack walnuts at their most vulnerable—husk-split stage. This makes management of both moth pests extremely important.

Doug Light, United States Department of Agriculture (USDA)/Agricultural Research Service (ARS) Western Regional Research Center in Albany, California, has been conducting research on mating disruption since the early 2000s.

“Twenty years ago I discovered a potent host plant odor or kairomone attractant from pears and it is called the ‘pear ester’,” Light said.

Pear ester attracts both male and female CM. Moreover, when a trap is baited with pear ester combined with the CM pheromone, males are attracted in much higher numbers.

Research has shown this is due to a synergistic enhancement and greater stimulation of male brains when pear ester accompanies pheromone, Light explained.

Fifteen years ago this combination of pear ester and pheromone was developed as a “combo lure”, that allows for effective accurate monitoring of CM in both conventional and most importantly in mating disruption treated orchards, that had no effective lure. This combo lure is the standard lure for monitoring CM worldwide, Light said.

Light and Joe Grant, emeritus UCCE farm advisor in San Joaquin County, demonstrated that pear ester and pheromone combined in a dispenser significantly reduces mating and nut damage.

For the last nine years Light has been conducting cooperative research with Grant and two other UCCE tree nut specialists, Emily Symmes, University of California (UC) Area Integrated Pest Management Advisor (IPM) for the Sacramento Valley region, and Jhalendra Rijal, also an IPM Advisor with the UC Statewide IPM Program in the San Joaquin Valley.

This team has been experimenting with passive dispensers for mating disruption that is simultaneously effective for both codling moth and NOW.

Two dispensers, one for each moth, are co-hung together using a pole. They are placed at 20 per acre at mid-canopy. They are easy to hang and labor efficient, Light said.

Using passive dispensers, researchers have seen a reduction in mating and nut damage by both pests.

“Hanging them together, we get very high results—over 95 percent disruption and reduction in male moth capture in pheromone traps of both codling moth and naval orangeworm,” Light said.

All of the past and ongoing research efforts will allow mating disruption to become a practical and useful tool for growers to use in their IPM programs for tree nut production.