Description of the Pest
The leaffooted bug is a sporadic pest in almonds. It gets its name from the small, leaflike enlargements found on the hind legs of the large nymphs and adults. Adult bugs are about 1 inch long and have a narrow brown body with a yellow or white zigzag line across its flattened back. The leaffooted bug overwinters as an adult in large groups on host plants near orchards. Overwintering bugs migrate from these sites into orchards in March or early April in search of food.
There are three species of leaffooted bugs that can be found in almonds. The most common is Leptoglossus zonatus. All three species are similar in appearance, except that L. zonatus has two yellow spots just behind the head (on the pronotum), L. clypealis has a thorn-like projection called a clypeus that extends forward from the tip of the head, and L. occidentalis has neither of these features. All three species have a white zigzag pattern across the wings: this patten is prominent in L. zonatus and L. clypealis and is relatively faint in L. occidentalis.
Although it is a sporadic pest in almonds, in years when weather and other conditions are right, significant damage can occur. Feeding by adult leaffooted bugs on young nuts before the shell hardens causes the embryo to wither and abort, or may cause the nut to gum internally, resulting in a bump or gumming on the shell. It can also cause nut drop. After the shell hardens, adult leaffooted bug feeding can still cause black spots on the kernel or wrinkled, misshapen nutmeats. Varieties with softer shells such as Fritz, Sonora, Aldrich, Livingston, Monterey, and Peerless are more susceptible to bug damage for a longer period during the season.
Be careful not to confuse leaffooted bug damage with damage by stink bugs. Both pests damage nuts by probing them with their needle-like mouthparts, and both result in gumming on the hull. In most cases, leaffooted bug damage occurs in March and April while stink bug damage is more common in May and June. Another way to distinguish damage, considering that symptoms are so similar, is to find the actual bugs or their egg masses; stink bug eggs are barrel-shaped and laid in clusters in contrast to leaffooted bug eggs, which are laid end-to-end in strands.
Egg parasites, Gryon spp., often keep populations of leaffooted bug below economically damaging levels. However, as egg parasites, they have no ability to control the overwintering adult leaffooted bugs that migrate into orchards in spring.
Monitoring and Treatment Decisions
Walk the orchard during the months of March and April to look for dropped nutlets (particularly on susceptible varieties), nuts with gummosis, and leaffooted bugs. Finding adult bugs is the best indication that a problem may arise, but the cryptic nature of these pests and their behavior of staying in the tops of trees make this difficult to do. A more practical approach is to look for nuts with gummosis or egg masses on the sides of nuts. If gummosis exists, cut a cross-section across the damaged site to look for a puncture mark from the bug's mouthparts to confirm that the gummosis is not due to physiological reasons. The easiest monitoring method is to look for aborted nuts on the ground. However, basing treatments on gummosis and nut drop also means that there can be a 7- to 10-day lag time between when feeding takes place and when gummosis and nut drop occur, so the dispersing insects may have already moved.
Treatment thresholds have not been developed for this pest in almonds, but low numbers of bugs can cause substantial damage. If bugs and their damage are evident, consider an insecticide application; apply insecticides from March through May to target the overwintering adults that have migrated into the orchard. Unfortunately, the broad-spectrum products that are most effective against leaffooted bugs are also very disruptive to biological control agents of spider mites and other almond pests. Later applications are not needed when numbers of overwintering adults have declined or nymphs are the only life stage present, as their mouthparts are too small to feed on the kernel.
|Common name||Amount per acre||REI‡||PHI‡|
|(Example trade name)||(hours)||(days)|
|Not all registered pesticides are listed. The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least harmful to natural enemies, honey bees, and the environment are at the top of the table. When choosing a pesticide, consider information relating to air and water quality, resistance management, and the pesticide's properties and application timing. Always read the label of the product being used.|
|(Brigade WSB)*||8–32 oz||12||7|
|MODE-OF-ACTION GROUP NUMBER1: 3A|
|COMMENTS: Do not repeat an application in less than 15 days. Spring applications may suppress or control peach twig borer and navel orangeworm. Can cause secondary pest outbreaks, especially spider mites.|
|(Warrior II with Zeon)*||1.28–2.58 fl oz||24||14|
|MODE-OF-ACTION GROUP NUMBER1: 3A|
|COMMENTS: Spring applications may suppress or control peach twig borer and navel orangeworm. Can cause secondary pest outbreaks, especially spider mites.|
|(Agri-Mek SC*, others)||Label rates||See label||See label|
|MODE-OF-ACTION GROUP NUMBER1: 6|
|COMMENTS: Provides control of adult bugs on contact but does not have any residual control once residues have dried. Also provides control of spider mites. May disrupt biological control of spider mites, particularly sixspotted thrips. Certain formulations emit high amounts of volatile organic compounds (VOCs); use low-VOC formulations. Regulations affect use for the San Joaquin Valley from May 1 to October 31, 2018 and 2019. Review the Department of Pesticide Regulation's updated fact sheet.|
|(Asana XL)*||9.6–19.2 fl oz||12||21|
|MODE-OF-ACTION GROUP NUMBER1: 3A|
|COMMENTS: Spring applications commonly cause secondary outbreaks of spider mites.|
|(Belay)||6 fl oz||12||21|
|MODE-OF-ACTION GROUP NUMBER1: 4A|
|COMMENTS: Provides partial control of adult bugs on contact but does not have any residual control once residues have dried.|
|‡||Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (PHI) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI. The longer of these two intervals is the minimum time that must elapse before harvest may occur.|
|*||Permit required from county agricultural commissioner for purchase or use.|
|1||Rotate pesticides with a different mode-of-action group number, and do not use products with the same mode-of-action group number more than twice per season to help prevent the development of resistance. For example, the organophosphates have a group number of 1B; pesticides with a 1B group number should be alternated with pesticides that have a group number other than 1B. Mode-of-action group numbers are assigned by IRAC (Insecticide Resistance Action Committee).|
|—||Not recommended or not on label.|