Last year was a tough one for California’s pistachio growers in their ongoing battle to curtail navel orangeworm damage. Damage to their crop from this destructive pest was the most ever. Stemming these losses and ensuring high quality isn’t likely to get much, if any, easier this year.
Almost all insect damage found when growers deliver their pistachios to processors is caused by NOW. Last year, for the first time, insect damage to the Fresno County crop exceeded 1 percent, reaching 1.47 percent. That compares to the 1.72 percent damage figure for Kern County, 2.12 percent for Tulare County (down a tad from 2.18 percent in 2012) and 2.31 percent in Kings County. These figures reflect 25,918 loads from Fresno, Kern, Kings, Madera and Tulare counties.
Part of the problem was an unusually large population of the worms that survived the winter inside mummies hanging in the trees and lying on the orchard floors, reports entomologist Joel Siegel, with the USDA-Agricultural Research Service’s San Joaquin Valley Agricultural Sciences Center in Parlier, Calif. Hot summer weather that encouraged development of an extra generation of NOW also contributed to increased pest pressures in the orchards. As a result, the standing population of NOW, which had been increasing for the past few years, grew even bigger, adding to the number of worms overwintering in the orchards. Warm winter weather didn’t help matters, either.
“We’ve missed the opportunity to kill off part of the NOW population this past winter,” Siegel says. “So, were starting the 2014 season with higher numbers of the pest than usual. Also, water shortages this year would add to the stress on the trees and probably lead to more early splits than normal. This, in turn, would allow the worms to get into the new-crop nuts sooner.”
As a result, says Siegel, this year’s crop faces unusually high pressure from NOW.
The best defense, he emphasizes, is proper orchard sanitation in the winter to remove mummies from trees and berms and to destroy them with disking. But, the job doesn’t end there. The key to controlling NOW for the rest of this growing season lies in following basic, common sense orchard management practices. “Focus on the fundamentals,” Siegel advises.
More from WFP
Here’s what he means:
Meet with your PCA to review your chemical, equipment, custom applicator and other needs to keep on top of any emerging NOW threat.
“For example, talk with your insecticide distributor to make sure the product you want to apply will be available when you want it,” Siegel says. “If not, have an alternative or two that you can order instead. In several cases in recent seasons, demand for certain products by farmers in South America or commitments made to other growing regions in the United States limited the availability of some materials used by growers here.”
Invest in your infrastructure
In this case, Siegel is talking about having enough equipment to treat all your trees in a timely manner. As he points out, the continued strong pistachio market of the past few years has enabled some growers to expand their acreage significantly. Now is the time to make sure that the number of spray rigs and tractors you own have expanded along with your acreage, he notes.
Make every drop count
Unlocking the full potential of an insecticide to control NOW requires applying the chemical as efficiently as possible. The travel speed of the sprayer plays a critical role. For an air blast sprayer, University of California researchers have found that an air blast spray applies chemicals most efficiently when it is operated at no more than 2 mph. At speeds above 2 mph, the ability of the sprayer to adequately cover the upper canopy of the tree drops rapidly. This drop-off begins at 12 feet. Any faster wastes material and reduces coverage and effectiveness of the treatment.
Siegel’s studies confirm that the minimum effective rate for applying a NOW insecticide with an air blast sprayer is 150 gallons per acres. “Shoot for 150 to 200 gallons per acre,” he says. “A lower rate, of course, reduces the amount of time spent on refilling the tanks. But effectiveness of your spray suffers. This gets back to having the proper infrastructure in place. Maybe you’ll need a nurse truck in the orchard to eliminate travel time back and forth to the shop to refill your sprayer so you can treat all your trees at the best time.”
Turn on the lights
Also, Siegel recommends spraying your orchard at night. NOW moths are active from dusk to dawn. Spraying then gives offers a better opportunity for the chemicals to contact more moths than during the day. Also, humidity levels in the orchard tend to be higher at night, reducing loss of chemicals through evaporation. Plus, winds usually die down after dusk reducing the potential for winds to carry the pesticide off site. In fact, nighttime application is routine in many West Side orchards because the wind has died down and is not a factor then.
Communicate and cooperate
As San Joaquin Valley growers continue to plant more ground to pistachios and other NOW host crops, including almonds and walnuts, populations of the insect and proximity of the host crops to each other increases as well.
“There are more opportunities for NOW to move from one orchard to another,” Siegel says. “That’s why it’s important for growers to talk with their neighbors and coordinate their efforts to control this pest.”
More from WFP