The Texas Department of Agriculture (TDA) has issued a second citrus quarantine area in the Texas Rio Grande Valley after a single grapefruit near Mission tested positive last week for Huanglongbing (HLB), or citrus greening disease. The new quarantined area includes a new five-mile radius zone surrounding the grapefruit tree where HLB was detected on Sept. 14.

According to officials with Texas Citrus Mutual (TCM), an industry support organization in the Valley, the tree is located in downtown Mission in a residential yard and was not part of a commercial citrus grove. TCM officials report 1,760 total acres of commercial citrus in the new quarantine area. This represents the second emergency quarantine zone established for the Rio Grande Valley.

The emergency quarantine limits movement of fruit and citrus stock from the grove to packing facilities and also the movement of citrus nursery trees from the quarantine zone.

Huanglongbing 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. HLB is considered to be one of the most serious plant diseases in the world and currently there is no cure, although promising research over the last year provides potential for new treatments.

 

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HLB is spread by the Asian citrus psyllid, a tiny insect that feeds on the leaves and stems of citrus trees. When an Asian citrus psyllid feeds on an HLB-infected tree, it can pick up bacteria that cause the disease. Once infected, a psyllid carries the disease-causing bacteria for life and can transfer the disease when feeding on other citrus trees.

The United States Department of Agriculture and the Animal Plant Health Inspection Service (APHIS) says detection of HLB can be difficult and citrus growers may not be able to find visual symptoms for up to a year after infection occurs. Generally, the first symptoms are yellowing leaves; however, citrus trees often have yellow leaves because of nutritional deficiencies, making detection that much harder.

Later symptoms of HLB-infected trees include lopsided, small fruit, and premature and excessive fruit drop. Additionally, the disease can cause entire shoots or branches of the tree to become yellow.

Disease first detected in San Juan in 2012

On January 13, 2012, the Texas Department of Agriculture (TDA) and APHIS confirmed the first detection of citrus greening in Texas. TDA immediately placed an emergency quarantine on the entire area for a 5-mile radius of the infected tree, which was located in San Juan near the Rio Grande River. An emergency quarantine of the five-mile area remains in effect although some details of the quarantine have been revised. No citrus nursery trees inside the quarantine area may be moved, and no citrus trees outside the quarantined area may be moved into the quarantined area except under a special permit issued by TDA.

State and federal agriculture officials warn that HLB is an extremely destructive plant disease that threatens the state’s citrus industry and detection of the disease in an orchard or grove constitutes emergency action.

On March 14, 2012, however, TDA issued an updated emergency quarantine that specifies conditions for movement of citrus nursery stock within and outside of the citrus zone. The citrus zone includes the following counties: Brooks, Cameron, Hidalgo, Jim Hogg, Kenedy, Starr, Willacy and Zapata.

Control of the insect is the only way to prevent the spread of the disease to other citrus trees. Even before the first infected tree was discovered in the Valley, citrus producers, aided by Texas Citrus Mutual, were participating in a voluntary spraying program on a regular schedule because the insect can be found in larger numbers across the Texas-Mexican border. Before the first case of HLB was uncovered in Texas, officials knew it was just a matter of time before the insect infected Valley citrus groves.

A more aggressive spraying schedule after that first detection is credited with preventing widespread infection to other Valley citrus areas.

History of HLB in the U.S.

The disease was first detected in the U.S. in June 1998 when a psyllid that carried the strain of citrus greening was found in Florida. Citrus greening is now confirmed in five states including Florida, Georgia, Louisiana, South Carolina and Texas.

As a protection for the citrus industry and as a preventive measure to slow the spread of the disease, mandatory treatments to control Asian citrus psyllid (in accordance with APHIS guidelines for interstate movement of citrus plants) will be required for all citrus nursery stock production in the citrus zone prior to movement within and outside of the affected zone.

Effective May 1, 2012, all citrus nursery stock produced in the citrus zone must be treated with an APHIS-approved systemic insecticide (soil drench) at least 30 days but no more than 90 days before shipment. This must be followed by an APHIS-approved foliar spray no more than 10 days before shipment. Treatment must be conducted with an APHIS and EPA approved product labeled for use on citrus in nurseries. Persons applying treatments must follow the product label, its applicable directions and all restrictions and precautions.

Approved products for treatment of nursery stock are as follows:

  • Baythroid XL (cyfluthrin),
  • Lorsban 4E (chlorpyrifos),
  • Admire 2 Flowable (imidacloprid),
  • Brigade 2EC (bifenthrin), and
  • Discus (imidacloprid/cyfluthrin).

As of January 18, 2012, TDA placed all citrus and orange jasmine nursery stock in the quarantine area under a seizure order. Effective March 14, 2012, citrus trees from locations outside of or inside of the quarantined area may be moved under special permit to a commercial citrus grove inside the quarantined area for planting. To request a special permit, contact the TDA regional office in San Juan at (956) 787-8866.

Texas Citrus mutual officials report the positive tree in Mission was detected by an ongoing USDA-APHIS sentinel tree survey. The tree has been tested before and citrus greening was not detected in previous samples. The infected grapefruit tree is large according to officials and because of the latency of disease symptoms, it may have had the disease for an extended period of time. USDA inspectors warn that this latency serves as a reminder of the challenges of early detection,which includes knowing what the early symptoms look like and where in the tree to look for them.

Officials warn that early indications are that symptoms are slightly different in Texas compared to other states where infected trees were found. Texas Citrus Mutual is planning upcoming producer meetings in the Valley to share that information with growers to aid in the process of early detection.

In addition, APHIS will be surveying all commercial groves within the new quarantine area beginning with those that are scheduled to be harvested first. If the APHIS inspectors have not finished surveying a producer's grove and grapefruit is ready for harvest, producers will be allowed to proceed with harvest.

Outreach efforts to target commercial growers and homeowners

Also, extensive plans have been developed for outreach efforts with homeowners in the quarantine area. The homeowner with the most recent positive tree voluntarily agreed to remove the tree and an additional citrus tree that was touching it, even though the second tree and all the other trees on the property were sampled and tested negative for the disease.

The two trees were removed by Texas A&M Citrus Center personnel Sept. 27, according to approved protocol procedures. The citrus industry and the team working on this new development say homeowner cooperation is appreciated as it greatly aids the commercial industry in controlling the spread of the disease.

Under the leadership of TCM, a new addition to the program will include more emphasis and suggestions on how to control psyllids at the interface between backyard citrus and commercial groves. There will also be more emphasis on having growers with properties in close proximity to one another treat their respective groves as close to the same time as possible.

TCM and state and federal officials say growers in the Valley should plan on attending upcoming meetings in both quarantine zones to discuss rules, limitations and strategies.

The Mission quarantine meeting will be staged Thursday, Oct. 10, at the Mission Chamber of Commerce meeting room where a free lunch will follow. All grove owners, growers and grove care managers within the new five-mile Mission quarantine area should attend.

The San Juan quarantine meeting is set for Wednesday, Oct. 23, at the Hilton Garden Inn in McAllen, registration begins at 11:30 a.m., a free lunch will also be provided for growers attending this meeting. All grove owners, growers and grove care managers within the five-mile quarantine centered in San Juan should attend.

In addition, two special zone meetings will be staged in the Valley. The Zone 1 area wide meeting will be held 8:30 a.m. Wednesday, Oct. 23, at Hilton Garden Inn in McAllen. All grove owners, growers and grove care managers within the five-mile quarantine centered in San Juan are invited to attend.

The Zone 2 special meeting is set for 8:30 a.m. Thursday, Oct. 24, at the Texas AgriLife Research & Extension Center, in Weslaco. All grove owners, growers and grove managers operating east of U.S. 281 should attend.

For more information or to RSVP for any of these meetings, interested parties should contact Hilda Castillo at 956-584-1772 or Hilda@valleyag.org.

According to TDA officials, the disease poses no threat to human health as it affects only the tree and not the fruit. The disease has caused serious economic damage to the citrus industries in Florida, Africa, Asia and South America, but so far control efforts have minimized damage in the Rio Grande Valley. Citrus producers and homeowners with citrus plants are asked to comply with quarantine measures to protect Texas citrus trees.

 

Also of interest on Southwest Farm Press:

New strain of HLB disease found in South Texas citrus grove

Researchers gain ground in citrus greening fight

Huanglongbing citrus disease confirmed in California