Vulnerability of almonds to leaffooted bug damage may be extended this year amid reports that numbers are much higher due to mild winter temperatures.
Almond is the first nut crop this large plant bug moves into after overwintering. The pest does not produce a new generation in almond because nymphs are not capable of accumulating sufficient nutrition.
“Usually they have moved on to pistachios by June 15, but that may not be the case this year,” said Kris Tollerup, entomology specialist at the University of California’s Kearney Research and Education Center. “Last year I did not see LFB in pistachios until the end of June, and I was searching a lot.”
Whether the extended stay in almonds means higher crop damage is uncertain.
Justin Nay, owner of IPM consulting company, Integral Ag, confirmed the higher numbers. Last year his field inspections yielded just four leaffooted bugs. This year he reports finding more than 60 with aggregations of seven and nine on individual trees with numerous mating pairs. Nay said his company has treated about 25 percent of their almond ground statewide with Yolo and Kern being the hardest hit by LFB. Treatments were also made in Sutter, Tulare, Madera and Colusa counties. Some ranches were not treated because they did not reach their in-house treatment threshold of one adult per acre.
Leaffooted bugs cause nut damage by using their piercing-sucking mouthparts to probe into leaves, shoots and fruit. Adult LFB can probe deeper than nymphs and can reach almond kernels. When they feed a digestive enzyme is excreted that causes staining on the pellicle.
Tollerup said LFB is a native of California and has been around for many years, but the high numbers and movement into crops such as almond and pistachio are relatively new. Leptoglossus clypealis was the predominant LFB specie at one time, but L. zonatus has become more common and is considered the most destructive. It is distinguished by two yellow spots just behind the head. L.clypealis has a thorn-like projection extending from the tip of the head.
Tollerup reports more sightings of L. clypealis and thinks their numbers may be increasing. This species is predominant in desert plants including palms and Joshua trees. L. Zonatus is most commonly found in nut crops.
Pomegranate is also an important host for L. zonatus. This crop is where the final generation of the year is born before it disperses in November for sites that provide better protection from weather. Tollerup suggests that pomegranate could be used as a ‘trap crop’ as LFB moves into this crop in September to lay eggs. Nymphs from that generation cannot fly and can be easily killed with a pesticide application.
“This could be a window of opportunity to knock back large populations,” Tollerup said.
Last year LFB began laying eggs in pomegranate during early September, and an entire generation was produced by the end of November, he notes. As temperatures cooled and the trees began to lose leaves, the adults moved to nearby palm and cypress trees to overwinter.
This spring they began to move in March in search of food. Tollerup advised monitoring for LFB activity through June with a focus on sites near pomegranates or overwintering sites. Visual monitoring should include inspection for gummosis on almond hulls as the season progresses. LFB feeding-induced gummosis appears clear to light amber in color while bacterial spot induces dark amber to orange gummosis.
Nuts found on the ground should also be inspected for gummosis and a stinging wound to determine if LFB caused the damage.
Tollerup said insecticides are most effective during the nymph stage, and pyrethroid materials work best. There is no treatment threshold recommended for LFB.