Some Florida citrus growers are experimenting with supplemental chemical controls to suppress Asian citrus psyllid populations.
They're adding perimeter, or wrapping, sprays aimed at psyllids in between regularly scheduled major pesticide applications over their entire groves. Focusing on borders and other hot spots can provide a quick and less expensive check to pest populations, says Michael Rogers, associate professor of Extension Center in Lake Alfred.
"Psyllids tended to accumulate on the outside of the grove," Rogers says. "Probably 80 percent of psyllids are found there."
Spraying only the outer edges allows applicators to cover more area in the same amount of time, making a broader swath to keep out fly-ins, says Frank Youngman, owner and president of Florida Grove Foggers in Lake Placid.
"If we can wrap four to five groves at a time, it creates a bigger buffer," Youngman says. "It's harder for [outside] psyllids to fly over."
Scout your groves to guide your decisions, says Brandon Page, Citrus Health Management Area program assistant at the university's Lake Alfred center. "If you're finding most [of the psyllids] on the edges and none in the center, you probably want to do perimeter sprays," he says.
But all three men emphasize that perimeter spraying should only supplement a full control program and not replace major overall sprays.
"It's a preventive practice to keep psyllids from moving in, but eventually they're going to get there," Page says.
By helping to hold down overall psyllid numbers, the entire control program has a better shot at slowing the spread of greening, the key disease that the pest vectors, Rogers says.
"It's not as expensive and can take the edge off the population between the big planned sprays," he says.
Part of a larger puzzle
A test of the practice in one grower's groves showed perimeter spraying reduced psyllid numbers by 70 percent to 80 percent between full-grove applications. Follow-up sprays are more effective because they're targeting lower populations, Rogers says.
Scouting reports across the state show a large drop in psyllid populations, Youngman says. But he attributes that to the combination of all the measures growers are deploying against the pest, with perimeter sprays only one piece of the puzzle.
A high percentage of the psyllids found in Florida are infected with the bacteria that causes greening, he says.
Holding down the populations and keeping the pest from traveling from one grove to another will reduce the rate of new tree infections.
A complementary pest-management tool
Perimeter sprays offer an additional tool for pest management programs, Rogers says.
In general, they're best used when psyllids go on the move, starting in the spring and into the summer, he says. The practice may provide less benefit in winter when the pest isn't as mobile.
But every grove is different, rarely perfectly square or straight-edged, Youngman says. A perimeter spray may need to hit only the outer edge or perhaps go a little deeper, into the first three rows.
Some groves may abut areas that pesticide applications don't always cover or that can provide hidden refuges for psyllids, such as myrtle bushes, he says.
Those irregular shapes and other physical constraints can demand extra effort to ensure that spray machines cover only the desired depth on grove borders, Rogers says. He suggests turning off nozzles on one side of the applicator to force sprays into border trees.
Low-volume is another option
Another option is using low-volume spray machines for night applications.
"We can do a thousand acres a night when no one else is in the grove," Youngman says. "It's half the cost to apply at low volume instead the full volume."
An added benefit is the chance to use lighter machines at higher speeds, factors that combine to lower environmental impacts, he says.
Adding perimeter sprays to a control program obviously increases the number of pesticide applications. That makes rotating chemical classes for resistance management more complex, Rogers and Youngman say.
Following rotation guidelines is crucial to maintaining growers' pesticide arsenal against psyllids. "The CHMA program puts a priority on resistance management," Page says. "We can't lose any one of these tools."
Hew closely to all pest management guidelines, not only when it comes to rotations, but also in following label instructions for rates, timing and so on, Youngman says.
"We want to keep the populations down, but we don't want to create super-psyllids," he says.
The other key component is to scout groves diligently in order to understand pest population trends, tree health and grove conditions, he says.
Youngman also suggests working with neighboring growers to share experiences with your control program. For instance, one material may perform better with a surfactant.
A psyllid outbreak next door has the potential to harm more than your neighbor's grove. "Fight as a unit, not as individuals," he says.