If Hurricane Irma didn’t do enough of a number on Florida’s citrus industry, in its wake lies a prime breeding ground for the Asian citrus psyllid (ACP). While ACP populations where fairly low right before the storm, numbers will be on the rise.
“The storm partially defoliated most citrus trees, which will induce flush that provides ample food for ACP to reproduce,” says Phil Stansly, a Professor of entomology with UF/IFAS. “In fact, trees already are flushing like crazy. I would expect we will be seeing much higher populations than normal within a month or so after the storm.”
He added that temperatures will be ideal for the ACP, so generations of the pest can turn over within three weeks or less. By the second generation, the buildup in populations will become more evident.
Spray Sooner Than Later
Stansly is advising growers the sooner they could spray for ACP following Hurricane Irma, the better.
“It’s always good to nip a new generation in the bud,” he says. “I wouldn’t wait for them to build up. Trees are stressed by wind and water damage from the storm, so allowing additional stress from re-inoculation with HLB would not be a good thing.”
But, with half the crop or more on the ground, the economics of aggressive ACP control gets even tougher.
“That is being stuck between the rock and the hard place,” Stansly says. “Unfortunately, the cheaper products are most overused with the consequences of resistance that we are seeing. At this point [soon after the storm], it is probably more important to get something on now and go with more selective products next growing season. I’d probably opt for an organophosphate like dimethoate or chlorpyrifos.”
Stansly added that growers who are able to make timely applications to mature trees after Irma hopefully would not need additional sprays until the dormant period. However, the first dormant spray could be moved up if off-season flush or high ACP populations are found earlier.
It is cautioned that growers be careful of potential tank mixes utilized in sprays to avoid stressing trees from hot application mixes.
“Growers usually want to put as much as they can in the tank to reduce the number of passes, but this practice can backfire,” Stansly says. “An aerial application with just the insecticide would be timely and relatively inexpensive. This would be a good way to go if feasible for individual growers.”
Brandon Page, Coordinator of the citrus health management area (CHMA) spray program, says it is too early to tell how the storm would impact the program. But, he added that ACP have already been at historically high levels in groves across the state this year.
“Most growers I have talked to are working hard to get their groves cleaned up and take an assessment of what impact the storm had on their operation,” Page says. “But, it is not too early to think about upcoming dormant sprays. In the past, dormant sprays have yielded great success in controlling ACP in the CHMAs.”
Lukasz Stelinski, an Associate Professor of entomology and nematology with UF/IFAS, has documented and confirmed cases of what he called an alarming rise of resistance of ACP to important neonicotinoid-based insecticides over the past season. Prior to the storm, he had advised growers refrain from using the materials as soil drenches in groves where growers were observing application failures and to instead apply neonicotinoids as foliar sprays. Regardless of how neonicotinoids are applied, he urged the importance of rotating them with other modes of action. New research shows neonicotinoids are more lethal on contact with ACP rather than when ingested via root-drench applications. The result is insufficient active ingredient in leaf tissue to kill psyllids, even in non-bearing trees, following soil drenches.
“Hurricane Irma has no impact on recommendations regarding ACP resistance management,” he says. “I would not change my spray protocols, if possible. An abnormally large flush after the storm might be a reason to adjust sprays, if the ACP populations take off.”
Stelinski agrees there will be economic forces directing growers’ ability to control the pest. But, he adds, where the ACP has not been controlled, populations of the pest have been high before the storm and that will remain true after the storm.