As a sporadic pest in California almond orchards, it’s difficult to predict when — or even if — the leaffooted plant bug will pose a threat in any given year. But, when it does strike it can cause significant damage, and quickly.
In the spring, it can feed on the nut hull, causing superficial damage. But, it can also use its needle-like mouth parts to bore through the hull and shell to feed on the kernel, causing the nut to turn yellow and fall to the ground.
In one University of California trial a single adult female, feeding on 10 to 12 caged nuts over a seven-day period, caused a 20 percent nut drop. And the damage doesn’t necessarily stop there. In the same trial, that adult bug caused damage to another 20 percent of the nuts that were visible at harvest.
After the shell hardens, feeding can still cause black spots on the kernel or wrinkled, misshapen nutmeats, This damage, which lowers the quality and value of the nuts, can’t be seen until the nuts are harvested.
Hilltop Ranch, which typically handles more than 25,000 tons of almonds annually, receives some shipments each year at its processing facilities at Ballico, Calif., that contain nuts damaged by the leaffooted plant bug.
“Depending on the year, the extent of that damage can range from minimal to serious,” says Paul Ewing, the company’s director of sales. “Usually, it affects no more than about 4 percent of the nuts we get in. That compares to navel orangeworm damage, which I’ve seen run as high as 20 percent in a load of nuts.”
Hard shell varieties are the most susceptible to injury from the leaffooted plant bug damage, he says; they include Butte, Padre, Mission, and Fritz. “This is quite unique, as most other types of insect damage occur in soft shell varieties, which provide easier access due to the softer shell.”
Injury to a nut by the leaffooted plant bug or any insect is classified as a serious defect. The USDA defines this as brown spot on the kernel, either single or multiple, when the affected area aggregates more than the equivalent of a circle one-eighth inch (3.2 mm) in diameter. Growers receive no payment for such rejected nuts.
Even if the leaffooted plant bug doesn’t cause obvious staining, damage from its feeding can become apparent after blanching. Consequently, processors and customers that blanch almonds are more sensitive to leaffooted plant bug damage, Ewing says.
Losing just two percent of a 44,000-pound load to the pest can be costly. Assuming a price of $2 per pound for defect-free nuts, that damages represents a loss to the grower of $1,760.
Processors can sell nuts with insect injury only as oil stock. Usually that’s worth only about 10 percent of the value of nuts without damage.
“It costs more to clean up a bin of nuts containing insect-damaged kernels than the damaged nuts are worth,” Ewing says.
Those costs include the extra handling needed to spot and remove damaged nuts and the need to slow processing speeds. Due to the nature of the damage, injury to unprocessed nuts caused by the leaffooted plant bug isn’t as easily detected by electronic sorting equipment as injury caused by other almond pests.
“Because stains created by the bug’s feeding are so small, the best way to find and pick out the damaged nuts is to sort them by hand,” Ewing says. “However, electronic sorters can efficiently remove damaged nuts after they’ve been blanched.”