Attempts to eliminate the dreaded Asian citrus psyllid, the pest responsible for the spread of citrus greening in Florida, may be playing a role in the resurgence of a pest that can set the stage for citrus bacterial canker.

It was around 1993 that the citrus leafminer first turned up in Florida.

The tiny worm burrows between cell layers of the citrus leaves as it feeds.

The openings it creates provide an entryway for the bacteria that cause citrus canker disease, which can render fruit unmarketable.

The leafminer itself can affect yields and stunt tree growth, says Lukasz Stelinski, assistant professor of entomology at the University of Florida’s Institute of Food and Agricultural Sciences Research and Education Center at Lake Alford.

Within a couple of years, scientists were able to control the citrus leafminer by introducing predatory wasps together with native wasp species in affected areas.

All was well until the Asian citrus psyllid appeared in 1998. When growers used insecticides to control psylla, they also killed the predatory wasps that fed on leafminers. The result was increased numbers of leafminers and a resurgence of citrus canker.

Weather and other conditions also may have played a role in the uptick in incidents of citrus canker, experts say. But most agree that decimating the predatory wasp population was a leading cause.

New solutions

Until now, growers have relied on conventional pesticides, such as soil-applied imidacloprid, to combat the leafminer. But researchers recently have come up with two new, pheromone-based materials that specifically target the pest.

One, called SPLAT-CLM, is manufactured by Riverside, Calif.-based ISCA Technologies Inc. The other, MalEx, is made by Portland, Ore.-based Alpha Scents Inc.

The two products are based on different technologies, Stelinski says.

SPLAT is a mating disruptor that is not yet registered.

“We can prevent the male from finding the female, and prevent the male from mating with them and prevent egg laying,” Stelinski says.

The Environmental Protection Agency accepted comments on the SPLAT registration through April 13. The Florida Department of Agriculture and Consumer Services has been working to expedite its registration.

MalEx also uses pheromones, but in a different way.

“Each droplet acts as an attractant for males that mimics a very attractive female, but each droplet has a small dose of toxicant,” Stelinski says. When the male touches the droplet, he dies “and is effectively removed from the breeding population.”

Both formulations are different from traditional insecticides in that they’re deployed onto the crop as “discrete blobs of paste,” Stelinski says.

“They can’t be applied by conventional agricultural sprayers,” he says, “so we’re developing an inexpensive and effective device” that growers can easily attach to tractors.

Advantages

One advantage of SPLAT is that it is specific to the citrus leafminer and will not harm beneficial insects, says Agenor Mafra-Neto, president and chief executive officer of ISCA Technologies. However, that also is a disadvantage for growers who hope to control more than one pest with a single spray.

Another major advantage is that SPLAT is applied in doses of just one dollop per tree, with no need to spray the whole grove.

Mafra-Neto estimates the cost at $125 per acre, but he says one application lasts 15 weeks or more, longer than most pesticide sprays.

He expects the cost to drop over time as production picks up and growers learn how to better apply it to meet their specific needs.

Mafra-Neto says he expected the Environmental Protection Agency to register SPLAT in April, with Florida registration following shortly thereafter.

Like SPLAT, MalEx is “very species specific,” says Darek Czokajlo, president of Alpha Scents. “We are going to kill only male citrus leafminers. We don’t kill any beneficials or other species.”

The product stays on the trees and does not reach the ground nor does it cover the fruit.

“Most of the formulation will end up on the foliage,” Czokajlo says.

MalEx, an attract-and-kill material, uses about 100 times less pesticide than conventional products and costs less than traditional sprays, he says. Czokajlo estimates the price at $60 per acre. He expects registration by the end of the year.

Good impressions

Preliminary impressions from growers seem positive.

Mickey Page, farm manager for the Mid-Florida Citrus Foundation in Winter Garden who has been involved in preliminary tests using SPLAT with Valencia oranges, is optimistic about its potential.

“It’s an exciting product,” he says.

It should work better than traditional insecticides, he says, it is not harmful and lasts a long time. Timing is not as critical with SPLAT as it is with chemical pesticides.

Keys to the product’s success, Page says, are finding an efficient way to apply it and making it available at a reasonable cost.

Tom Stopyra, technical crop adviser for Packers of Indian River Ltd. in Fort Pierce, says the leafminer is “a huge problem, especially if you’re a grapefruit grower.”

He’s hopeful that one of the new technologies will work.

“I don’t care which one it is,” he says. “It’s got to be economically feasible.”

Contact Citrus + Vegetable at vlboyd@att.net or (209) 571-0414.