HLB-Spreading Psyllids: Dormant Sprays and the Edge Effect

University of Florida entomologist Phil Stansly discusses the use of dormant sprays for HLB-spreading psyllids. He also addresses the fact that psyllid populations are often higher on grove perimeters — the so-called “edge effect.”

Stansly says the next coordinated grower spray for psyllids in the Gulf citrus-growing region will be a dormant spray. “The trees are dormant now and that’s what we’re looking for,” he says. “The advantage to that is that psyllid populations are now decreasing because there’s no reproduction; there’s no flush. Also we’re looking at some pretty dry weather here so we ought to be able to keep the residual in long enough to kill those psyllids … We started experimenting with that (dormant sprays) in 2006 and we saw how effective it was, that a single dormant spray was still effective well past the spring flush.”

HLB was discovered in Florida in 2005. The Gulf was the first region to institute area-wide coordinated sprays to control the Asian citrus psyllids that spread the disease. Only later were citrus health management areas created to coordinate grower sprays in wide areas around the state.

Regarding the edge effect, Stansly says, “The edge effect is real. I think every grower can see it … It’s the fact that we see higher numbers of psyllids around the edges of the blocks, especially when they’re facing an open area. I expressed the opinion that it’s psyllids that are flying out of the block, but they stop when they see that there’s no more trees … We think it has to do with psyllid behavior and the visual response to not seeing trees.”

Stansly told growers about the psyllid issues at a recent citrus health management area workshop in Immokalee. The workshop was coordinated by Gulf Citrus Growers Association Executive Vice President Ron Hamel and multi-county citrus Extension agent Mongi Zekri.