By Peter Chaires
The Florida citrus industry recently gained access to a newly approved HLB therapy for use on bearing citrus. In addition to new applications in the use of 2,4-D and gibberellic acid, growers now have a 24(c) special local needs label supporting direct application (injection) of oxytetracycline.
It is no secret that industry recovery will require some combination of tolerant or resistant varieties and more effective therapies to restore production and quality while the industry is transitioning to its new reality. The 24(c) label represents a new use pattern of an existing antimicrobial material.
Grower reaction to the availability of direct application methods for bactericides as a means of reducing Candidatus Liberibacter asiaticus (CLas) in citrus trees has varied. Some growers are going to take a wait-and-see approach, and some have no intention of using it. But others view it as the only card they have remaining to play and appear to be excited to move full-steam ahead with applying this product.
PROMISING RESULTS
Public and private experiential research indicates that trees treated through direct application will begin their road to recovery in the first year. Those mainstay varieties needed to sustain the Florida citrus industry will be a logical starting point for this therapy. Round oranges will undoubtedly get the most attention, followed by some level of focus on grapefruit. Growers will look to see a restoration of root zone and canopy first, as Mother Nature slowly restores the root-to-shoot balance of the tree. If all goes well, and the program is administered as designed, fruit quality, size and quantity should return over the next couple of years. It will take some time for growers to become proficient in managing this program, but quality customized training is available.
Perhaps a secondary area of focus will be those varieties that have not performed well in an HLB-endemic environment. Case in point: navel oranges. Florida navel orange trees continue to look good, but many growers have struggled with fruit quality, cropping and consistency in the HLB era. Navel oranges have long been a small percentage of the Florida orange crop, but they have also been a product of great importance to commercial packinghouses and gift fruit/roadside operations for generations. The prospect of again producing the navel orange of old is of great interest to large and small growers.
Key limes have recently been propagated in quantities beyond the perceived needs of the dooryard market. Presumably, they are being planted for commercial purposes. Considering the susceptibility of key limes to HLB, these plantings may also benefit from experimentation with direct application of oxytetracycline.
TREATING MOTHER TREES
There is a third tier of interest in direct application that is a little more obscure. Florida growers have been exposed to a range of fresh market varieties in recent years that showed early promise for fruit quality and productivity but failed to perform consistently in subsequent small grower-based trials. There are many theories why this occurred. Perhaps the warm falls had an impact, or the trees reverted to some level of juvenility.
Because the mother tree was able to grow and establish a full canopy and root zone prior to the stress of its first crop, it stands to reason that newly budded trees infected with HLB from infancy would not perform in the same manner when bearing the stress of fruit in the second year. Some growers are interested in using direct application methods to see if, once treated, the tree and fruit performance more closely resembles that of the mother tree. If the degraded fruit quality, drop and overall tree health were primarily the result of HLB susceptibility, this should become readily apparent. If the poor performance was due to a myriad of factors, it may take longer to figure out and resolve. Stay tuned.
Peter Chaires is executive director of the New Varieties Development and Management Corp.