Navel orangeworm (NOW) is an early riser who stays late, making it the primary, season-long pest for California pistachios.
In research by Joel Siegel and others, NOW eggs have been found as early as January in Kern County. Siegel, USDA-ARS research entomologist at the Kearney Ag Center in Parlier, Calif., told more than 300 people at the statewide pistachio field day in Visalia, Calif., that NOW has four generations per season extending into early fall when it can be most damaging to splitting hull pistachios ready for harvest.
Those January eggs are not likely to develop into worm pests. However, the second generation eggs laid at the beginning of February produce the next generation that is currently well underway in the San Joaquin Valley. Siegel said growers should presently be monitoring for emerging worm populations and be ready to treat for them.
NOW is not just a grower problem, but it can impact marketing since NOW damage invites aflatoxin, which can make people ill. The niche market pistachio industry does not need another food recall after the industry was hit by a salmonella scare last season that resulted in the recall of 16 million pounds of nuts.
Pistachio production is expanding rapidly in California, where more than 90 percent of American pistachios are grown. With millions more pounds reaching consumers comes greater chances of a food-borne issue if the industry does not remain vigilant. The industry has stepped up with more stringent farming and auditing guidelines.
California’s pistachio industry has grown from the first commercial harvest in 1976 of 1.5 million pounds from 4,500 acres to the 2007 production of 416 million pounds from 103,000 acres. There are now about 112,000 bearing acres and 80,000 nonbearing acres which will come into bearing over the next five years.
According to the Administrative Committee for Pistachios, California produced about 354 million pounds last season. This was considerably lower than original crop estimates of more than 400 million pounds.
This year’s crop could be near the 2009 production due to the rapidly expanded acreage, even though 2010 will be an off year, according to some industry processors. The last off year was 2008 when 277 million pounds were produced.
Compounding the worm problem — NOW likes a lot of crops. It is a major pest of almonds. Although NOW emerges sooner in pistachios than almonds during the season, generations peak at the same time in both crops.
Navel orangeworms are travelers. Siegel said 2 percent NOW damage in pistachios has been recorded traceable to almonds 3 miles away. “Poorly managed almonds can impact neighboring pistachios.”
Sanitation is the first line of defense against NOW in pistachios, like it is in almonds. Yet, there are differences.
Sanitation involves getting rid of mummies, knocking them off trees and blowing mummies away from berms followed by disking and shredding. However, there are some questions about the value of shaking pistachio mummies from trees, since what is left in the trees may be mostly blanks and not as susceptible to harboring NOW.
More pistachio mummies are likely to be found on berms than almonds since this is the focal point of the pistachio harvest. Pistachios are harvested with catch frames, so the nuts do not touch the ground. Almonds are shaken to the ground without catch frames. Almonds are windrowed and swept up.
Pistachios not caught by the catch frames remain on berms where moisture can “glue” them to the ground, making it difficult to blow them into drive rows where they can be disked in or otherwise destroyed. Tree row irrigation systems are the prime source of this “glue.”
Siegel’s research has found that as many as half the nuts remain on the berm after blowers are used to push them into the drive row due to this glueing effect.
In a trial several years ago, more than 227,000 mummies were collected form the berms in an 80-acre block of pistachios. In another 160-acre block, almost 360,000 mummies were gathered. Obviously, not all spawned NOW in the spring, but enough did to support a stringent sanitation threshold of just 0.2 mummies per tree and a ground mummy threshold of just four nuts per tree. These numbers represent a sanitation level of 99.6 percent of the mummy nuts destroyed.
Even when buried as deep as 6 inches, research has discovered that NOW larvae can still survive and emerge.
Control is challenging. Overwintering immatures may emerge over a five-month period.
Insecticide control sprays can be applied from late April to July. Once NOW infects the open-hull nut, insecticides cannot penetrate the shell to kill the worms.
Speed does not kill when applying pesticides for NOW control. Siegel told the growers and others in Visalia that traveling at 3.5 miles per hour with a spray rig versus 2 miles per hour, reduces control by 90 percent.
Last year’s salmonella forced the industry to re-evaluate its Good Agricultural Practices (GAP) manual first written in 2000.
While not legally required, many pistachio handlers are asking growers for documentation of on-farm activities as part of their due diligence for consumers. Bob Klein of the California Pistachio Research Board said processors may require growers to adopt GAPs and document them with a self appraisal of farming practices.
These audits can cover a wide range of areas from the sources of irrigation water to fertilizer and pesticide use. The CPRB audit covers 35 to 40 areas. It is all about reducing risks, said Klein, who reminded growers to document all they do.
“If you did not document it, you did not do it,” said Klein.