Living with HLB - Area-wide integrated management system for ACP in Texas
Article written by Sara Garcia Figuera and Mamoudou Sétamou. Edited by Monique Rivera, Peggy G. Lemaux. Posted January 11, 2021.
What is the technique?
Texas is the third largest citrus-producing state in the US, with 65% of its citrus acreage focused on red grapefruit production for the fresh market. Most commercial citrus groves in Texas are located in the southern end of the Lower Rio Grande Valley (Figure 1), where the Asian citrus psyllid (ACP) was first detected in 2001 and the HLB bacterium in 2012. Since then, both have spread throughout the region and are now established, putting Texas citrus production under grave threat.
The area-wide integrated management system (AIMS) was developed for Texas citrus growers to control ACP populations on a landscape scale and maintain citrus production at a profitable level, even with widespread HLB. AIMS consists of three coordinated area-wide insecticide sprays (pyrethroids, organophosphates, neonicotinoids in conventional groves and biopesticides including mineral and plant oils, pyrethrins and/or kaolin in organic groves), two during the dormant period, in November and February, and one in mid/late August, before the September rains that trigger profuse flush (new leaf growth) production. Scouts, hired by the Texas Citrus Pest and Disease Management Corporation, call the growers in each of the two management zones to let them know when it is time for the coordinated dormant sprays, and organic growers are asked to spray twice for each conventional spray, at the beginning and at the end of each spray window. Additional sprays are recommended in individual properties at the onset of each flush cycle during the active growing season, from April to September. To time these individual sprays at the most effective moment, growers need to monitor the ACP populations and flush on the grove borders. When there is flush, it is as if citrus trees had turned on a green light for the ACP, so it is crucial to spray right when ACP adults are present and start reproducing. These sprays can be combined with pesticides targeting other pests and diseases, thus the concept of integrated management.
How does it improve HLB management?
By targeting the ACP population on an area-wide scale, focusing on several individual properties at the same time, citrus growers can minimize ACP movement between groves and prevent transmission of the HLB bacterium. The two main objectives of AIMS are: (1) to reduce ACP populations during the overwintering period, while citrus trees are dormant, so that populations are at their lowest level when they start reproducing at the onset of citrus growth and; (2) to prevent ACP reproduction on citrus flush. ACP inject the HLB bacterium when they feed, and they exclusively lay their eggs on citrus flush. When the eggs hatch, nymphs feed on infected flush and acquire the bacterium, transmitting it to other trees when they become adults and fly away. Therefore, coordinated sprays lower the ACP population at the end of the fall and before the spring flush, and individual sprays timed before each flush cycle prevent ACP reproduction on flush, reducing HLB transmission. AIMS has been successful at keeping the ACP populations low and maintaining citrus production in Texas at a profitable level. Indeed, a gradual year-to-year reduction of ACP populations industry-wide has been observed since the inception of this program ten years ago in January 2010 (Figure 2).
Who is working on the project?
Dr. Mamoudou Sétamou, Professor of Entomology at Texas A&M University-Kingsville Citrus Center, developed AIMS in close collaboration with Drs. David Bartels and Matt Ciomperlik scientists at APHIS-PPQ in Mission, Texas, and the Texas citrus industry and continues to work with the industry to develop new tools and refine existing approaches.
What are the challenges and opportunities?
In the Lower Rio Grande Valley, commercial citrus groves are interspersed with residential neighborhoods with abundant backyard citrus trees, so there is a constant movement of ACP from backyards to groves, and vice versa. This poses a significant challenge when trying to manage ACP at a landscape scale, because homeowners are not used to controlling for pests, and most are not willing to remove their valued citrus trees in order to prevent infection with HLB. Because of this, the biocontrol agent, Tamarixia radiata has been released in residential neighborhoods to reduce ACP populations. Despite the influx of ACP from residential citrus, AIMS has been successful at maintaining ACP populations at a low level. This strategy was developed building on experiences learned from Florida and adapting them to Texas conditions. In turn, because Texas is at a more advanced state of the HLB epidemic than California, there is an opportunity for California to learn from the experiences acquired in Texas to optimize the area-wide management program that has been implemented in Southern California.
Funding source: We express our sincere gratitude to USDA APHIS-PPQ for funding through the Citrus Commodity Pest Survey Cooperative Agreements.