There are three legs to the stool where control of the Navel orangeworm sits, says Brad Higbee, director of entomology research for Wonderful Orchards.
And one of those legs has grown shakier over time – the use of a particular class of prized chemicals that was highly effective and relatively inexpensive.
Higbee and David Haviland, University of California integrated pest management advisor in Kern County, discussed the challenges to managing pyrethroid use against the Navel orangeworm (NOW) and other pests.
Both also talked of another leg of the stool – “Sanitation, sanitation, sanitation,” Haviland said.
And Higbee emphasized the third leg, another weapon in his arsenal as he seeks to keep NOW at bay: mating disruption.
The men pointed out that repeated pyrethroid use has fostered resistance in pests, and both advocated making certain that different classes of pesticides are used.
Higbee said, “A 2015 field was treated with Warrior and at most we killed 30 percent (of adults exposed to residue). Five or six years ago, we would have killed all of them. We’re seeing a reduction in the efficacy of pyrethroid products.”
He said permethrin has little impact on NOW, and pyrethroid tank mixes are now required. Higbee believes in “loading up on residues” close to harvest.
In discussing IPM and pyrethroids, Haviland said they still have some efficacy and their price remains low.
“I’m not here to say, ‘Don’t use pyrethroids.’ Just don’t use them more than necessary. Don’t spray if you don’t have to.”
When spraying, he adds, use a high label rate “enough to kill.”
Haviland said the most important spray timing – in order of importance – is at hull spray, after hull split, and at early split.
He recommends monitoring for damage, taking into account how many nuts are expected to fall off naturally and whether beneficials including phytocoris – “which can also be a bad guy” – pose a problem.
If you can preserve the phytocoris, particularly during the early May window, it may be best, so it can eat the eggs of NOW’s first generation, Haviland says.
Higbee said application of pesticides can be challenged by the fact “intimate contact with larvae and eggs” is required. He said they are only on the hull, and adequate coverage is difficult to achieve. Reaching nuts higher in the tree is a challenge.
Higbee said the tolerance for damage from NOW has become lower and lower.
“My marching orders are 1 percent or less.”
“It makes sense to do as much as you can,” Higbee said. But he said it is especially hard to predict risk of NOW damage in pistachios where pest populations tend to be higher than in almonds.
“We’ve looked at no sanitation and full sanitation,” he said. “Full always lowers damage. But we don’t know if we do nothing, how much damage we will have.”
He said mummies on the ground pose the greatest risk, and that mowing and disking are equally good at destroying mummies. Sweeping the orchard floor also helps.
Higbee says the NOW moth is highly mobile and can travel more than half a mile per night. Enlisting help from neighbors in treatment helps bolster effectiveness.
As pistachio prices have risen in recent years, he says it could pencil out to use more costly chemicals and other approaches and be worthwhile as growers shoot for damage of 1 percent or less of the crop.
The cost per acre, Higbee says, can amount to $5 to $10 (per acre) for pyrethroids, $40 to $50/acre for new chemistries, and $120/acre for mating disruptions. And growers also benefit from processor incentives to achieve low damage levels.
At the same time that some earlier popular pyrethroids have shrunk in usage in recent years, the nut acreage where mating disruption is used has risen.
In 2013, this amounted to 32,000 acres using NOW mating disruption. It grew to 60,000 in 2014, and to an estimated 120,000 acres in 2015. Higbee expects it will reach 200,000 acres this year – in both almonds and pistachios.
The worldwide registration for mating disruption products rose dramatically from 1978-2008.
When Higbee first started using a sex pheromone for mating disruption in pistachios, he said, “I wasn’t crazy about it. It doesn’t work well in high populations, and populations were higher in pistachios than in almonds. But we did it and it worked well.”
Higbee is also part of an industry task force looking at a way to add a fourth leg to the stool of NOW control. This leg includes a pilot project in the experimental stage that would draw on facilities previously used to rear, sterilize, and release massive numbers of sterile pink bollworm moths. This project seeks the release of millions of sterilized NOW moths, and would likewise work best when populations of the sterile pest are low.
Meanwhile, Higbee touts successes of mating disruption, saying it can help reduce NOW damage “generally by 50 percent.”
“The best fit currently is in orchards where current insecticide programs are not sufficient,” he said. “It’s most effective when added to an existing insecticide program.” In some cases, it can reduce the number of sprays needed.
Pheromones can be provided in micro-capsules, hand applied, or in timed-released puffers. The capsules are applied at between 10-100 per acre. Hand-applied passive release devices are applied at 100-200 per acre. Puffers are used at 1-2 per acre.