Ask Your PCA: What progress has been made to eradicate citrus greening?

Chris Boisseranc 
Southwest Ag Consulting Inc., Redlands 

The Asian citrus psyllid, or ACP, is almost microscopic in its immature stages. The insect can carry and transmit citrus greening, a bacterial disease also known as huanglongbing, or HLB. 

HLB rates in California are extremely low compared to Florida, where the state lost 80% of its citrus production. California’s relatively low infection rates can be attributed to the state’s drier conditions, which do not allow the trees to continually produce flush growth. Most of California’s bacteria pressure from HLB is in residential settings in Orange, San Diego and Los Angeles counties, with a small amount in Ventura County. 

Currently, there are only insecticidal spray treatments to control the pest and still no treatment for the bacteria. However, there is research underway to treat the bacteria through different delivery systems that go deeper in the tree.

Trunk injection of oxytetracycline has proven effective in reaching the phloem and significantly reducing bacterial loads in leaves and roots during the span of one month. Scientific analysis has confirmed that trunk injection is far more efficient than foliar sprays.

Researchers at Purdue University are developing plant nanocarriers that can be applied to leaves and travel through the phloem to reach the roots and trunk—where Liberibacter, the bacteria that causes HLB, resides. It mimics other delivery systems and aims to overcome the limitations of conventional sprays.

Researchers are also searching for resistant varieties that can tolerate HLB disease. This could potentially allow the tree to maintain health and vigor even if it is diseased. It has been done in grapes with Pierce’s disease—the finding of a zinfandel variety tolerant to the disease. 

There are certain species of citrus, such as the finger lime and other microcitrus, that are completely resistant to the disease. A more radical approach is to create oranges out of lime genetics so that they also carry the resistant traits of the microcitrus varieties.