Growers and PCAs, particularly in the lower San Joaquin Valley, are being warned to be on the lookout for excessive early season damage from leaffooted plant bugs and other large plant bugs.
Bob Beede, University of California Extension farm advisor for Kings County, issued an alert after numerous reports of leaffooted plant bugs feeding in almond orchards in southern Kern County near Maricopa.
Heavy rainfall the valley has experienced this winter and spring encourages growth of host vegetation, supporting larger populations of the overwintering adult insect, he notes.
Research by Kent Daane, UC insect ecologist, also shows greater winter survival in years with fewer hard freezes.
“It’s very important to get out in the orchards frequently, preferably twice a week, to detect early any injury by leaffooted plant bugs or stink bugs so pesticides can be used most cost-effectively,” he says.
“Be on the lookout for clear gumming on the surface of almond hulls and epicarp lesions on pistachio nuts caused by the feeding insects. Migration from surrounding seeded or succulent vegetation into orchards should increase with warmer weather.”
Orchards next to native vegetation and such host crops as pomegranates, olives, citrus, and Italian cypress and juniper trees, are especially vulnerable to invasion by the adult insects, which are strong flyers.
Fritz and Monterey almonds are more prone to attack from the insect than Nonpareil, Beede says. Hard shell varieties, which leaf out a little later than soft shell types, have slightly smaller nuts that may be more succulent and attractive to the leaffooted plant bug as overwintering adults migrate into orchards.
However, Daane’s research shows that kernel damage decreases markedly once almond shells harden. After hardening, clear gumming can still be observed on the hulls, indicating the continued presence of leaffooted bugs or stink bugs in the orchard. Spotting of almond kernels can also result from their feeding.
Pistachio kernels remain susceptible even after shells harden, causing black spots (kernel necrosis), limited botryosphaeria infections, and some damage from yeast infection.
The insect can be difficult to spot in trees. “In addition to staying in the tops of trees, they tend to avoid discovery by moving around to the back side of nuts as you approach them,” Beede says. “Beating the foliage with a stick or a shovel handle can force them into flight.”
In almonds, feeding damage from leaffooted plant bugs causes fruit drop. “If you see a significant amount of fruit drop, you should assume that the insect has been present in the orchard for at least three, if not five, days,” he says.
Typically, the leaffooted plant bug doesn’t move into pistachio orchards until June, when the season’s first generation of adults is produced.
“Crop consultants have reported achieving good control of the insect in almonds with Lorsban,” Beede says. “The University of California is extremely hesitant to suggest using pyrethroids early in the season on almonds because of the potential to kill a large percentage of parasites and predators needed to control web-spinning spider mites later in the season.
“This is especially a concern in Kern County and on the West Side where these spider mites often become very difficult to control without parasitic wasps and predators that feed on them.” Lorsban, an organosphophate, is disruptive to beneficials.
In pistachios, fourth and fifth generation pyrethroids can be used to control leaffooted plant bugs as well as stink bugs and navel orangeworms, Beede says.