Focus on disease and insects
By Kevin Ong, Ph.D., and Erfan Vafaie
Protect Citrus; Know the Enemies
EVERY COMMODITY HAS ITS own suite of insects and plant diseases, slowly chipping away at your ability to make a livelihood. Citrus, which has been reported to contribute roughly $460 million to Texas’ economy, is one that has been hammered particularly hard. A suite of regulations on plant movement and production containment requirements inspired by a few recent lethal pests and diseases make this a particularly difficult commodity, to say
TNLA Green November/December 2019
the least. Let’s explore two diseases and their association with insect pests, which is impacting the citrus production and ornamental citrus industries. CITRUS GREENING
Citrus greening, aka Huanglongbing (HLB), is a bacterial disease that has caused massive havoc to the citrus industry in Florida since it was detected in the early 2000s. In Texas, the presence of this pathogen was confirmed in 2012.
Thankfully, large losses in commercial citrus production have not been reported in Texas, perhaps due to education and proactive treatments and lessons learned from Florida’s experience. In the U.S. the most common species associated with this disease is Candidatus Liberibacter asiaticus (cLAS). This is a “fastidious” bacterium, meaning it is almost impossible to grow outside the plant, thus making detection of this pathogen only possible through molecular detection tools. Currently, this disease is found to be fairly widespread in South Texas. Recently, the quarantine for HLB has been expanded to more counties on the Texas Gulf Coast. For quarantine information, visit www.texasagriculture.gov and click on Regulatory Programs. This bacterium, Candidatus Liberibacter asiaticus (cLAS), is vectored by the Asian Citrus Psyllid (ACP). The Asian Citrus Psyllid (Diaphorina citrus Kuwayama), as its name implies, was originally widely distributed in southern Asia. Like aphids, mealybugs, and whiteflies, psyllids are a sucking insect pest that produce honeydew, resulting in the growth of sooty mold on the infested plant. There are several other species of psyllids that can feed on citrus but are not of particular concern because only ACP is known to be the vector of Candidatus Liberibacter asiaticus. cLAS, the causal agent of HLB, can be transmitted from infected to healthy trees through grafting, or more commonly by ACP, first discovered in Florida in 1998, in Texas in 2001, in Southern California in 2008, and in Arizona in 2009. The actual citrus greening pathogen was first found in Florida in 2005. All it takes is about one hour of feeding by an infected psyllid to transmit the virus to a healthy plant.