The issue isn’t about what scientists know about the leaffooted bug (LFB). It's all they don’t know about controlling the pest that is bothersome.
The bad news, according to University of California Integrated Pest Management Advisor Kris Tollerup, is the pest is hard to kill and canh decimate an almond crop.
Scientists are still searching for good news, though not all is doom-and-gloom.
“If growers are diligent to start monitoring in March they can protect their crops with pyrethroids,” Tollerup says.
Tollerup spoke to pest control advisors at the annual California Pest Control Advisor meeting recently, telling the audience that active research continues to look for better methods to control the pest, which has the ability to effectively overwinter in popular crops and protected areas.
The pests are particularly troublesome in almonds, pistachios and tomatoes, according to Tollerup, though citrus and pomegranates can host the pest as well.
The University of Florida reports that LFB-damage in citrus can include premature color break and fruit drop.
Leaffooted bug is particularly long-lived – upwards of 60 days, and generally with three overlapping generations per year. In recent years, Tollerup says the pest has successfully bred to a fourth generation in the San Joaquin Valley because of the mild winters.
In almonds, the pest can damage maturing nuts after moving into the orchards in March and April.
Damage occurs when the pest feeds on the maturing nut causing gummosis, nut drop and kernel necrosis. University of California guidelines suggest cutting open nuts with gummosis to inspect for evidence of puncture marks from the bug’s mouthparts. Gumming can also be symptomatic of disease not related to the LFB, which is why inspecting gummed nuts is important.
Similar damage in pistachios can happen from LFB, according to Tollerup. Epicarp lesions, aborted kernels and kernel necrosis can happen by LFB feeding in late May and early June.
Later in the season as the nuts harden, particularly in almonds, Tollerup says LFB can become less of an issue as they are unable to feed through the hard shells.
The critical monitoring period for LFB remains March through mid-July, Tollerup says. That’s when they can do their most damage to maturing almonds and pistachios.
There are effectively no traps to survey for LFB and available sticky traps end not to work as the pest is able to simply walk across the surface of the trap, he said.
Tollerup has tested and studied several different colors and types of sticky traps, but none seem to work. Furthermore, there are no pheromone lures.
Sweep samples can work for small bugs with beat samples more effective with large bugs.
Moving into the winter months, the pest will likely be found aggregating in citrus and pomegranates. For those with pomegranates, Tollerup recommends after harvest that trees be stripped of any remaining fruit and all fruit tilled into the soil.
Some studies seem to suggest that LFB is affected by sub-freezing temperatures, which is generally why the past few years in the San Joaquin Valley have been easy on the pest. Studies Tollerup conducted suggest that temperatures below 27 degrees for at least six hours can knock back LFB populations.
“This can certainly give us a heads-up if leaffooted bug is going to be a problem next year,” he said referring to cold winter temperatures.
Tollerup and other researchers have looked at different chemical controls for LFB. The most effective compounds were the pyrethroids. Chlorpyrifos was also effective for about a week or two in one study Tollerup cited.
In another study, Brigade, an insecticide labeled for citrus but not tree nuts, was killed 100 percent of the LFB population out to 21 days.
Aside from pyrethroids, there is little else in the grower’s tool box to control LFB in tree nuts.
UC IPM guidelines say that treatment thresholds for LFB have not been established for almonds. Tollerup says that this is one of those pests that, even in very low numbers, can cause substantial damage in an orchard.
Further troubling, according to UC IPM guidelines, is the broad-spectrum chemical controls available against LFB are quite disruptive to biological control agents of spider mites and other almond pests. Use of these products can disrupt good IPM practices in such cases.
Tollerup says there are some products that can deter LFB from feeding on host plants, but the work is tentative, so he is not prepared to make a recommendation.
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