By Dr. Kris Tollerup, University of California Cooperative Extension area-wide IPM advisor
It is the time of year when leaffooted bug (LFB) starts leaving aggregations to begin feeding, so pest control advisers and growers must be on the lookout. Although cold winter temperatures have the potential to significantly reduce overwintering populations, it appears that cold temperatures in the fall and winter of 2015–2016 had no significant negative impact on leaffooted bug. This year, very large overwintering populations on pomegranate have been reported to UC Cooperative Extension advisors. As in 2015, it appears that 2016 has the potential for large LFB populations to cause considerable economic damage on almond.
Overwintering aggregations of LFB range from five to 500 individuals, and in the San Joaquin Valley generally occur on citrus, olive and pomegranate, and on protected areas such as pumphouse structures and palm fronds. Almonds planted in close proximity to an overwintering crop, most notably pomegranate, have a greater potential of sustaining damage early in the season (March through May). Neighboring host crops should be monitored for overwintering aggregations, and as almond nuts begin to form on the closest orchard perimeter, the overwintering host should be most closely monitored.
Monitor March to May
Monitoring should occur at least once a week from mid-March through May, and then every one to two weeks through June. Visual surveys provide the most effective monitoring method for detecting the presence of the bug. Do this by positioning yourself so that the sun is behind you; then, use a long pole to knock branches in the upper tree canopy. This causes leaffooted bugs to fly such that they can be seen or heard.
Importantly, visual monitoring should include inspection for gummosis on almond hulls; note, however, that damage is occurring/has already occurred if gummosis on nuts is being observed. When inspecting nuts with gummosis, cross-section the area to determine the presence of a pin-sized discolored wound caused by the penetration of the insect’s mouthparts. This is important, since gummosis also occurs due to physiological damage. Gummosis caused by LFB feeding appears clear to light amber in color, while bacterial spot causes gummosis dark amber to orange in color. Additionally, inspect fruit on the ground for the presence of gummosis and a stinging wound to determine if LFB caused the damage.
Almond Board–Funded Studies
Insecticides provide the only known method for managing leaffooted bug. Studies funded by the Almond Board of California in 2014 determined that the pyrethroids bifenthrin (Brigade) and lambda-cyhalothrin (Warrior II) provided excellent contact and residual activity against adult bugs for two to four weeks. The organophosphate chlorpyrifos (Lorsban Advanced) also had excellent contact activity and provided one week of residual control. Also in the study, three other insecticides containing abamectin (Agri-Mek), sulfoxaflor (Sequoia; label pending) or clothianidin (Belay) provided moderate to excellent activity when sprayed directly on the bugs, although once dried, these insecticides did not provide any residual activity. It is important to note that Belay has a California registration on pomegranate and growers have reported favorable results when applied in spring against LFB on pomegranate.
Insecticides should be used only if monitoring indicates the presence of leaffooted bug and/or its feeding damage. Apply insecticides only after considering the potential risks of the compound to beneficial organisms, including bees and biological control agents, and to air and water quality. For more information on these topics, please consult the UC IPM Pest Management Guidelines for Almonds.
