Because both leaffooted plant bugs and stink bugs overwinter as adults, the earlier the better you is when growers and PCAs should begin checking for their presence.
Snooze and the damage can be costly to both almonds and pistachios.
Leaffooted plant bugs and most stink bugs move into orchards from their wintering areas, usually outside the orchard. However, one stink bug (Acrosternum hilare) will overwinter in the orchard. In pistachio orchards this species is often found by crews as they prune the trees in winter, notes Walt Bentley, IPM entomologist with the University of California’s Kearney Agricultural Center in Parlier, Calif.
“Acrosternum is the one to be very aware of, because damage can occur so quickly, as weather warms and young nuts are susceptible,” Bentley says. “In some instances, leaffooted bug will also winters in orchards. A local consultant has often seen this. So, knowing what species is damaging nuts and where they are wintering becomes quite important in limiting damage.”
The key is to get into the trees to scout for the bugs, or to examine the orchard for damage they cause by feeding on the nutlets, he notes. It doesn’t hurt to examine plants outside the orchard, either. Pay attention to London rocket, shepherdspurse and vetch, Bentley advises. “If you have open areas near orchards where there is Russian thistle be particularly aware of Euschistus spp., a common stink bug found on the west side of the San Joaquin Valley.”
Both the leaffooted plant bug and the stink bug damage almonds and pistachios, by feeding on the nuts. Each uses its mouthparts to pierce through the hull to feed on the nuts in their early stages of development. Leaffooted plant bug damage occurs in March and April, while stink bug damage is more common in May and June. Some almond varieties are more susceptible to leaffooted bugs than others. They include Fritz, Sonora, Aldrich, Livingston, Monterey and Peerless. If these varieties are used as pollinators for Nonpareil and they are the only varieties with nutlet drop, stink bug may be the cause, Bentley adds.
Once the shells harden, the insects are unable to kill the embryo.
The best indication of a problem is the presence of adult bugs, which tend to sun themselves on sunny days. However, they are very elusive and tend to stay in the tops of trees. As you approach a tree containing the insects, the bugs will move to the other side of the tree or branch, climb higher up in the tree or fly away.
Leaffooted plant bugs are longer, thinner a little larger and even more secretive than stink bugs, Bentley notes. The adult leaffooted plant bug makes a loud buzzing sound when it flies. “They sound almost like a humming bird in flight,” he says. “If you’re not seeing the bugs but you hear that sound, they might be in the orchard.”
Beating trays can be used to find the adult bugs. Bentley suggests holding the lid of a garbage can under a branch while rapping the branch with a mallet or lightweight club to dislodges the bugs to fall onto the tray.
Often, masses of the eggs and damaged nuts are the only practical way to detect the presence of the leaffooted plant bug or stink bugs
Leafooted 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. In almonds they are often found on the hulls of the nuts.
Feeding by leaffooted plant bugs and stink bugs before the shell hardens can cause the embryo to wither and abort. Also, they can cause gumming inside the shell and outside where strands of sap ooze out of the puncture or sting point in a spiral-like fashion. “If you see this, cut a cross-section across the damaged site to check for a puncture market from the bug’s mouthparts indicating that this gummosis is not due to physiological reasons,” Bentley says. Feeding at this time can also cause nuts to drop
After the shell hardens, feeding by these bugs leaves a dark, pinpoint stain on the shell at the site of the sting. This causes darkening of the nutmeat, which can become wrinkled or deformed, and an off-flavor.
“These large plant bugs are not a problem annually and not in every orchard,” Bentley says. “So, spending a short time walking the orchard after nut set can give you an idea of any potential problems.”
More information is available online at the UC IPM web site – www.ipm.ucdavis.edu/PMG