Leaffooted plant bugs and most stink bugs are the snowbirds of the insect world — they like to stay warm in winter.
They usually overwinter in warm places like pump houses, wooden barns and elsewhere before they move into orchards in the spring as the weather warms. And that’s when they can cause considerable damage by puncturing young nuts.
They are shy, particularly the leaffooted plant bug. They sense movement and actually scurry around to the backside of fruit and leaves when a person approaches. This makes them hard to scout. The very elusive plant bugs like to stay in treetops, which is also where they go when they sense movement.
The best way to determine if plant bugs are in the orchard is to look for feeding damage on the nutlets.
Both the leaffooted plant bug and the stink bug feed on almonds and pistachios, using mouth parts to puncture the hull and feed during early stages of nut development. This can cause the embryo to wither and abort. Damaged nuts can also fall from the tree.
Once shells harden, the insects are unable to penetrate the hull and kill the embryo; however, there may be damage beneath the hardened shell. Look for dark, pinpoint stains on the shell, which could be sting sites. The nut may not have been damaged enough to abort, but damage will be there. When hulled and shelled, the nutmeat of the damaged almond will be dark, wrinkled, or deformed and may be off flavor.
Leaffooted plant bug damage usually occurs in March and April, while stink bug damage is more common in May and June. This year, though, the cool, wet weather could be throwing off that timing.
Look first in Fritz, Sonora, Aldrich, Livingston, Monterey and Peerless varieties, which are the most susceptible to leaffootted plant bugs. If these varieties are used as pollinators for Nonpareil and they are the only varieties with nutlet drop, stink bugs may be the cause.
You can differentiate between the two plant bugs by noting that leaffooted plant bugs are longer, thinner, a little larger, and even more secretive than stink bugs. The adult leaffooted plant bug makes a loud buzzing sound when it flies, almost like a hummingbird.
You can also beat them out of trees. Hold a metal or plastic garbage can lid under branches and rap the branches with a rubber mallet or a small bat. This will dislodge the plant bugs and they will fall into the garbage can lid.
However, damage may be the only way to determine if plant bugs are in your orchard. Look for egg masses or damaged nuts to detect the presence of leaffooted plant bugs or stink bugs
Leaffooted bug eggs are brown and cubic in shape, and are laid in a series, like a string of boxcars. In almonds, they are found on hulls and leaves and in pistachios on leaves, twigs and nuts. Eggs of stink bugs are laid in clusters, are barrel-shaped, and have concentric dark rings at the top.
Gumming inside and outside the shell is another way to detect their presence. Strands of sap often ooze out of the sting point in a spiral-like fashion. If you see this, cut into the damaged area and look for a puncture mark to make sure the oozing is for physiological reasons.
More information is available online at the UC IPM website — www.ipm.ucdavis.edu/PMG