When you see adult leaffooted bugs (LFB) in your almond or pistachio orchards, it is time to take action.
There is no established threshold for economic damage caused by this piercing-sucking pest, said Kris Tollerup, UC Cooperative Extension area Integrated Pest Management advisor. Traps and lures for LFB are still being evaluated. Visual observation of LFB in an orchard should prompt treatment, advisors said.
This large insect pest is a native of California, and has been found in the San Joaquin Valley from Butte to Kern counties. While LFB may be found in most valley locations, there are specific environmental conditions that allow for populations to build. Those conditions include riparian areas, protected overwintering sites and host plants. Almond and pistachio orchards adjacent to those sites can become infested and are vulnerable to crop loss or damage from LFB.
Tollerup said he has seen a 50 percent almond crop loss in an orchard where LFB feeding early in the growing season caused nuts to drop from the trees.
Leaffooted bug species include Leptoglossus zonatus, L. clypealis and L. occidentalis. Their name comes from the small, leaf-like projections on their hind legs. Adults in all three are about 0.75 to 1 inch long and have narrow brown bodies with a white zigzag pattern across the wings. Zonatus, which has become the dominant LFB specie in the San Joaquin Valley, can be identified by two yellow spots just behind the head.
Leaffooted bugs’ overwintering capability can lead to high populations in the spring. This insect pest can tolerate temperatures down to 21 degrees F for six hours, Tollerup said. Milder winter weather and this species’ ability to find shelter are factors in higher infestation rates in orchards. This pest is commonly associated with pomegranates that provide a feeding/reproduction site after nut harvest. But, it is also finds shelter in ornamental perennial plants including palm and cypress trees. These pests also seek shelter in eucalyptus trees and outbuildings.
Almond and pistachio orchards adjacent to riparian sites and other prime overwintering sites are more likely to suffer LFB feeding damage, Tollerup said.
Last year, Tollerup said he was in a fifth- leaf almond orchard adjacent to a somewhat neglected pomegranate planting. The orchard lost half its crop due to a large population of LFB feeding on the nuts early in the season.
Overwintering sites that provide adequate shelter are springboards for the next generation of LFB to hatch in the spring. Adult LFB that survive winter can lay more than 200 eggs in string like strands on host plants. Nymphs emerge from the eggs about one week later and develop into adults in 5-8 weeks. Adults can lay eggs over an extended period, creating a population that includes all life stages by late June. During the spring and summer there are typically two to three generations of LFB. In the fall, all LFB develop until they become adults. These will overwinter in aggregations.
Adult leaffooted bugs’ mouthparts can pierce developing nuts to suck out juice. These mouthparts comprise more than half their length and allow them to probe deep into fruit in search seeds. Nymphs have less of an impact when feeding, generally only extracting plant juices. According to UC IPM Guidelines, LFB excretes digestive enzymes when feeding to liquefy a small part of the seed so that it can be ingested. Tollerup hypothesized that the enzyme also stains the pellicle of almond kernels.
Management of LFB
Tollerup said almond growers and pest control advisors should begin scouting for adult LFB in March. If LFB are present in the orchard, they are more likely to be found on the sunny side of the tree. No lures or attractants are available to monitor for LFB presence, Tollerup said, but observing adults, and finding signs of feeding on nuts would indicate a need for control.
Pistachio growers and pest control advisors should look for adult LFB in April and May when they move into orchards to feed and lay eggs. There is no economic threshold for LFB in pistachio, Tollerup said. If adults are observed in the trees, growers or managers will have to decide if the numbers warrant a pesticide application.
The most effective control materials for LFB are pyrethroids due to their residual activity. Tollerup said these products, if applied correctly, could provide control. Other management strategies include removal of host plants if possible. Removal of weedy areas that serve as a food source during winter months can also help keep LFB numbers down.
Both pest control advisor Justin Nay and University of California Cooperative Extension (UCCE) specialist Houston Wilson agreed that almond and pistachio blocks with a history of LFB infestations are most likely to have recurring infestations. This year appears to be a light year for LFB, Nay said. Infestations that were found were in the blocks in areas that get them almost every year. Total amount of nuts lost for his growers was very small, with the worst blocks losing less than one percent.
In April a few of the almond blocks Nay watches had enough LFB to justify a treatment, but the total was only a small fraction of blocks under his supervision. Blocks were in both the north and south and in areas that get LFB every year.
Nay’s pistachio blocks were just starting to meat fill in early July, and it was too early for LFB to move into that crop.
Wilson has been part of a research effort to find an effective trap and attractant for LFB to improve monitoring. This information can fill a critical gap in control as predicting population densities and overwintering survival early in the season can assist with control efforts.
While use of pyrethroids has been an effective control measure, resistance to that material has built in navel orangeworm and growers are using more targeted pesticides that are not as effective as pyrethroids on LFB.
He said the hanging panel trap is currently being used as a platform to test various types of lures. Lures are both pheromone based and host plant volatile based.