Many of us are attracted to shiny objects. It appears the opposite may be true for Asian citrus psyllids, the carrier of citrus greening.
Citrus greening, also called Huanglongbing (HLB) or yellow dragon disease, is one of the more serious diseases of citrus. It’s found in all major citrus growing regions except the Mediterranean and Australia. The bacterial disease is spread by tiny insects called psyllids. The Asian citrus psyllid (ACP) is the species that is causing havoc in Florida groves.
Trees that are infected may not show symptoms for years, but eventually symptoms will develop such as yellow shoots, blotchy leaf mottle and vein yellowing on leaves attached to those yellow shoots.
Fruit from infected trees are small, misshapen and show some green color even on ripened fruit, which is how the disease took on the name ”greening.” Yields drop and fruit that is produced is worthless because of small size, poor color and a bitter taste.
There is no cure for greening. Scientists hope eventually to find and breed trees that are resistant to the disease. At the moment, the usual treatment is to use pesticides to kill the psyllid, in hopes of thinning their numbers.
Two Immokalee-based University of Florida researchers may have a better idea. Dr. Scott Croxton and Dr. Philip Stansly conducted a trial last year using metalized mulch to repel the psyllids. They found that the shiny covering significantly reduced psyllid populations and incidence of HLB compared to white mulch or bare ground.
The shiny, reflective surface may confuse the insects, preventing them from finding the trees.
The next step for the researchers was to take the show on the road. Last July, they formed a collaborative partnership with A. Duda and Sons with funding provided by the state’s Citrus Research and Development Foundation. Duda provided trees and a 10-acre block of grove land south of LaBelle.
“We planted the block in July 2012,” said Joby Sherrod, manager of research and development and technical services for Duda. “We wanted to help Drs. Stansly and Croxton, and we were very interested to see if the metalized plastic mulch does in fact have an effect in repelling the psyllids and ultimately slowing the spread of greening into these new plantings,” he said.
The plots are grown several different ways: some with mulch; some without. Some are treated with insecticide; some are not. Some receive nutrients; some do not.
And results are coming in now. “We are seeing strong repellence of [the psyllid] by reflective (metalized) mulch,” Stansly said. “For the latest sample, only one out of 1,000 young shoots on mulch was infested, compared to 10 percent on bare ground — a hundred-fold difference. Furthermore, no flush was infested on mulched trees treated with an insecticide drench. Thus, results so far indicate that the combination of metalized mulch plus insecticides provides best [psyllid] ACP control to young trees,” he said.
“The trees are growing well and looking good,” Sherrod added.
The researchers found in their initial experiment that the mulch may provide additional benefits. Used in combination with a drip irrigation and fertigation system, the mulch increased soil moisture, reduced weed growth and increased tree growth. “The enhanced growth is likely due to increased light being reflected up into the trees,” Sherrod said.
The metalized mulch seems to work best with young trees, which are more vulnerable to disease than mature ones. The active growing period of the young trees attracts psyllids to them rather than to the less vigorous older trees.
The trial was funded for three years. After that, it is assumed that the trees will be large enough to completely cover or shadow the mulch, preventing any light reflection and rendering the mulch ineffective.
Might the metalized mulch be incorporated into Duda’s production practices? “If the mulch is found to be effective, then we would consider using it on a large scale,” Sherrod said.
Learn more about the trial and the metalized mulch here.