The navel orangeworm caused relatively little damage to the Kern County pistachio crop in 2011, says Brad Higbee, research entomologist with Paramount Farming Company in Bakersfield, Calif. — but low damage levels last year don’t necessarily mean NOW numbers were down.
“Unlike other crops, there’s no definite correlation between the size of NOW populations and the amount of damage the insect causes in pistachios,” Higbee says. “The population of NOW in Kern County always tends to be high, but that doesn’t always translate into a high amount of damage to the crop.”
Last year, his company processed the first loads of harvested pistachios in early September. Less than .1 percent of those nuts showed NOW damage. Pistachios are most susceptible to NOW when mature, and damage levels tend rise as the harvest gets later and nuts remain on trees longer. That was the case last year. By the end of harvest in mid-October, about .5 percent of the nuts being delivered had been damaged by the insect.
Higbee’s involved in several research projects aimed at reducing the NOW threat in pistachio orchards even more.
Insecticides can be used during the growing season to protect pistachios. Because of labeled pre-harvest intervals, however, insecticides are not always effective at protecting nuts until harvest.
Harvesting mature nuts as early as possible can minimize NOW damage. But limited harvesting and processing capacity often stretches beyond the ideal 24 to 48 hours to process the nuts to minimize NOW damage.
Higbee is investigating how to improve orchard floor sanitation practices after harvest. As with almonds, nuts remaining in the orchard provide a home for NOW larvae to overwinter. The more mummies left in the orchard, the greater the threat the following year.
Mummies in the trees after harvest can be removed by shaking and poling. Paramount is able to reduce tree mummies n to only 1 in every 10 almond or pistachio trees, Higbee says. But, the task of clearing mummies from the orchard floor is much more difficult in pistachios than almonds.
Sanitation practices in almond orchards usually clear the ground of all but about 5 or 10 mummies per tree. However, the number of mummies missed by conventional ground sanitation practices in pistachios may total in the hundreds per tree.
“Flail mowers do a great job shredding almond mummies, but not pistachio mummies — it’s like trying to mow marbles,” Higbee says. “Disking isn’t very effective in sanitizing floors in pistachio orchards, either. It doesn’t bury all the nuts, and the larvae of navel orangeworm can survive burial as deep as six inches.”
This year Higbee will be testing the effectiveness of various modifications to existing harvesting equipment for improving removal and shredding of mummies on the orchard floor. The research is being partially funded by a grant from the USDA’s Technical Assistance for Specialty Crops program.
“We’re doing the initial equipment tests this year,” he says. “If the results show promise, we’ll expand to large-scale replicated trials next season.”
Reducing the number of overwintering NOW could enhance the success in another Higbee research project — disrupting NOW mating through use of pheromone puffers. The disruption techniqueuses synthetic pheromones to mimic the scent emitted by female NOW to confuse males and limit their ability to locate females.
“Mating disruption hasn’t worked well in pistachio orchards in the past because of the high NOW populations usually present in the spring,” Higbee says. “But, if we can improve winter sanitation to reduce NOW numbers in the spring, mating disruption might work. That would help keep the orchard protected all the way through harvest.”
Efforts to develop a pheromone lure that traps NOW date back several decades, he notes. The stumbling block has been in stabilizing the synthetic product in the field.
“We think that hurdle has finally been overcome and we’ll be doing major testing this year. Depending on the results, a commercial pheromone lure for monitoring NOW in pistachio orchards could be available next year.”
The lure trap would be put in the orchard in early spring and would remain effective for five to six weeks before it’s replaced. Trapping aids growers in applying insecticides more timely.
“For growers who use NOW egg traps and typically don’t see many eggs in July, August and September, the puffer would be a real eye-opener,” Higbee says. “It would give them a much better idea of the actual NOW populations throughout the season. It could be a huge benefit in developing a more reliable program for managing the insect.”