Researchers at the Texas A&M Citrus Research Center in Weslaco are warning that the Texas citrus industry will not be able to stop the spread of Huanglongbing (HLB), or citrus greening disease, unless homeowners across the Rio Grande Valley are made aware of the risks to citrus trees and citrus ornamentals in their yards and gardens.
Heidi Arteaga, the Texas AgriLife Citrus Greening Project Coordinator for the Valley and Citrus Greening Project Director at Texas A&M Kingsville Citrus Research Center, says while Valley citrus growers have done and continue to do a lot to curb the spread of the disease in commercial groves, infected trees recently discovered in the backyards of residential homes could pose a problem to curb the spread of the disease.
"A lot of homeowners aren’t aware of the risk involved in having citrus trees on their properties, which is why we need a lot of community meetings to get the word out, in particular during the ‘Winter Texan’ season, to educate people about citrus greening and control," says Arteaga. "We provide the public with a list of treatment methods and advice on which pesticides are recommended by the Extension service. We also work with homeowners to introduce a colony of predator wasps that can help to manage the psyllids that spread the disease."
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HLB is a bacterial plant disease that is not harmful to humans or animals but is fatal for citrus trees. The disease destroys the production, appearance and economic value of citrus trees. Diseased trees produce bitter, hard, misshapen fruit over time and the tree will die within a few years of being infected if not removed immediately. Each female psyllid, the insect that carries the disease, can lay up to 800 eggs and some trees have been found infested with over 40,000 psyllid.
Because it may take years before there are visible signs of the bacterial infection on the tree, the disease has ample time to spread. Infected trees die within 3 to 5 years in most cases. Because it takes several years before newly planted replacement trees can produce the volume of fruit needed to be profitable, the disease could devastate Texas groves and jeopardize the $200 million plus positive economic impact created by the industry.
Disease is spreading
The first outbreak of the disease in the U.S. occurred in Florida after the psyllid arrived on the East Coast from the Far East. But Dr. Olufemi “Femi” Alabi, plant pathologist at the Texas A&M AgriLife Research and Extension Center in Weslaco, warns movement around the Valley can be caused by a combination of both the infected psyllid or by moving infected nursery stock.
"Do not move plant materials indiscriminately” warns Alabi. “The primary way this disease currently spreads over long distances and from place to place is through infected tree materials. When you are not sure of the status of a particular tree’s material, make sure you do not move those materials to a different location.”
Researchers say that while the average commercial grower in the Valley is aware of and is treating regularly to control the spread of the disease, the greater problem seems to be spread of citrus greening disease from backyard plant to backyard plant.
"We must eliminate the movement of the disease among homeowner trees. It does little good to stop the threat at the commercial grove if we do not stop spreading the disease house to house," says Dr. Raul Villanueva, Assistant Professor and Extension Specialist and a citrus entomologist for Texas A&M Research and Extension Center in Weslaco.
He says awareness programs like the ones Arteaga is staging across the Valley help to inform and educate the average homeowner, and this, he says, is required to finally get control of the disease across the Valley.
Arteaga has been meeting with community leaders, college students, civic clubs and the general public as much as her schedule allows. Since she started the campaign of making the public aware of the risks associated with transmitting the disease from backyard to backyard, she has met with thousands to pass along the warning.
"I have made presentations to nearly 90 RV parks so far, making Winter Texans aware of the risks and enlisting their help in providing assistance. They have been very responsive and interactive in helping to slow the progress of the disease by monitoring citrus trees at their parks and around other locations," reports Arteaga.
Arteaga and Citrus Mutual President Ray Prewett addressed the 68th annual meeting of the Subtropical Agriculture and Environments Society Feb. 21 at the South Texas College Mid-Valley campus and updated attendees with the latest information about the status of the disease.
Homeowners who have citrus trees on their property can call Arteaga on a special hotline number for information and help on scouting and treating their trees. She said the program is still looking for homeowners who have citrus trees on their property to participate in a treatment program involving the introduction of parasitoids, in this case, tamarixia radiata, or small Pakistani wasp.
"We are looking for homeowners with lemon or lime trees between 8 and 12 foot tall to participate in this beneficial project," said Arteaga.
Once a homeowner test tree is qualified, Arteaga and team trim the tree to create new thrush, young growth which the psyllid requires to feed and lay their eggs.
"The thrush attracts the psyllid, and during this process we build a metal frame around the tree. We check back after two weeks and see if there are enough psyllids on the tree, then we stretch a mesh material across the frame, creating a tent that traps the psyllids inside. We then introduce a small colony of tamarixia which feed on the psyllid and multiply. After another couple of weeks we check population levels and then remove the mesh, allowing the new colony of tamarixia to freely move to other infected citrus trees across the area," she explained.
In this way, the small wasps are helping control the spread of the disease-bearing psyllids in both commercial groves and homeowner backyards all across the Valley.
For more information, call the citrus greening hotline to report a tree or to inquire about participating in the program. Call 956-580-1917.