For almonds: Leaffooted bug causes big damage

The leaffooted plant bug has long preferred pistachios where it causes fruit-aborting epicarp lesion, among other problems.

However, the highly mobile, large insect that can grow to almost 1 inch long, also likes almonds and munched away this spring, logging crop losses as large as 50 percent in almond orchards over a wide geographic area.

University of California Cooperative Extension entomologist Kent Daane told a grower/PCA field meeting in Chowchilla, Calif., hosted by Madera County UCCE farm advisor Brent Holtz, that in most years leaffooted plant bugs do not reach damaging levels in almonds, but a combination of factors turned it into a major pest in 2006.

These included:

  • Mild winter temperatures helped a large percentage of the fall '05 population to overwinter.

  • Spring rains provided an abundance of winter weeds for this overwintering population to thrive.

  • Cool April weather allowed the large population of big leaffooted bugs to synchronize its movement from overwintering sites into almond orchard where that same cool weather delayed shell hardening, making young nuts more susceptible to the insect pest.

These large pests had stronger mouthparts to penetrate the outer shell of almonds for a longer period of time this spring, according to Daane. Leaffooted bugs particularly enjoy attacking varieties like Sonora which are softer-shelled than varieties like Nonpareil.

However, the shells of all varieties were soft in the spring of '06, making all almonds susceptible to the leaffooted bug.

When the pest feeds on young nutlets from March through May, it creates a hull gumminess. Feeding from April to July can damage the interior shell and possibly cause fungal diseases in the kernel. This late-season feeding can downgrade deliveries to the huller.

Daane said there could be two- to-three overlapping generations per season.

It is difficult to sample for leaffooted bugs since adults will fly away or hide behind leaves or twigs rather than drop onto beating trays.

Daane said this is important to understand because the most critical sampling period is early spring when only adults are in the orchard.

While UC IPM guidelines for pistachio call for treatment when there is one leaffooted plant bug per 15 to 20 beats, there is no economic threshold established for almonds.

Daane said it is probably more effective to search for almonds with gumminess, cutting across the penetration site to see if the damage is only superficial and in the hull only or if the kernel is damaged.

“Growers and PCAs will need to make their own decision on whether or not a spray is needed” using factors like number of bugs and damage found; susceptibility stage of the nuts; variety and the tolerance of damage relative to crop load.

Daane points out that PCAs should also understand that gumming and nut drop occurs seven to 10 days after feeding takes place and treatment when damage is recognized likely would be too late to be effective.

Traditionally, an egg parasitoid that only has a long, scientific name provides natural control. However, this parasitoid was not effective this spring.

The UC entomologist said chemical control with Lorsban, pyrethroids or permethrin should be applied in April or May to kill overwintering adults that have migrated into orchards, if populations are high enough to cause economic damage.

However, some of these products may flare mites.

Also, Daane said growers may consider an Imidan or permethrin treatment in hull-split sprays for navel orangeworm to reduce leaffooted bug populations as well during the month before harvest to minimize dockage at the huller.

Daane believes one of the best ways to control this insect is to spray with pesticides where it overwinters outside orchards. The insects congregate and overwinter as adults in woodpiles, old wooden boxes, barns, pump houses, cracks in tree trunks, under the bark of eucalyptus trees and in cypress and juniper trees. Daane said he has seen huge numbers of leaffooted bugs in these areas.

Daane said the leaffooted bug is a strong flyer and moves from these areas far away from an orchard to feed on almonds in April and May.

He will be looking at attract and kill techniques next spring to control the insects where they overwinter rather than waiting until they reach the orchard where they are more difficult to control.

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