A five-mile quarantine prohibiting the movement of Valley citrus stock from an orange grove where the state’s first case of citrus greening disease was discovered earlier this month near San Juan, Texas, will remain in effect according to a panel of plant disease scientists representing the Texas Department of Agriculture (TDA) and USDA’s Animal and Plant Health Inspection Service (USDA-APHIS).

The decision was made Friday, Jan. 27, after field inspectors reported a grapefruit tree in a grove across the road from the orange grove where the disease was first uncovered tested positive for the disease.

In a statement late Friday TDA officials said there is no change in the five-mile emergency quarantine zone. Under guidelines of the quarantine, plants that can host the disease and are within a five-mile radius of the infected tree cannot be moved from the quarantine area. The disease poses no threat to human health as it affects only the tree and not the fruit itself. Citrus fruit harvested within a quarantine area must be free of leaves, stems, plant debris and any Asian citrus psyllid prior to movement outside of the area.

Dr. Juan Anciso, a Texas AgriLife Extension Service citrus specialist in Weslaco, says early detection of the disease and an ongoing comprehensive multi-year psyllid control program in the Texas Valley gives local growers “cautious optimism” that the disease can be confined to the quarantine area.

Homeowner trees

But according to a Texas A&M AgriLife report, local growers warn there is some concern over homeowner citrus trees that may not have been part of the psyllid control program. But inspections on both commercial and residential citrus trees have been ongoing for the last 3 to 4 years and until early January all tests were returned negative.

“We’re withholding judgment until inspectors can complete their assessment. Right now we don’t have enough information until inspections across the quarantine area are complete. But we are hopeful the disease is isolated to the quarantine zone,” Citrus Mutual President Ray Prewett said last week.

Citrus Mutual, a grower organization that has been active in organizing local growers in an effort to control Asian citrus psyllid (ACP) populations in the Valley since first discovered in 2008, reports almost all commercial citrus operations have voluntarily participated in control efforts, including the grower who owns the grove where the first case of citrus greening was discovered.

The Asian citrus psyllid, Diaphorina citri Kuwayama, was discovered in Florida in 1998, and can be one of the most serious pests of citrus if the pathogens that cause citrus greening disease, or huanglongbing (HLB), are present. The Asian citrus psyllid is responsible for spreading the disease and has long been detected in Texas, but confirmation of citrus greening disease in the Valley this month represents the first confirmed report of the actual disease in the state. Citrus greening, first identified in 2005, has destroyed hundreds of thousands of acres of citrus in Florida. It also has been found in Georgia, South Carolina and Louisiana.

Prewett says comprehensive inspections are taking place across the quarantine area to determine if other trees have been infected. But early identification of the disease can be problematic as symptoms are slow to develop.

“Citrus plants affected by citrus greening may not show symptoms for some time. On average, latency persists for approximately 2 years,” Prewett says.

As the pathogen moves within the tree, whole branches and eventually the entire tree may progressively turn yellow, but initially inspectors must carefully examine each tree within the quarantine zone for first signs of the disease.

“The state citrus industry has been closely focused on preparing for the day we knew was coming, when citrus greening arrived,” Prewett said. “We have already begun implementing response plans.”