by MIKE ROBERTS
Citrus Tristeza Virus was once a major citrus pathogen in Florida and outside, killing nearly 100 million trees worldwide. Citrus Tristeza Virus causes a disease called Tristeza decline, which reduces the production of citrus trees and eventually kills them, similar to citrus greening.
The impact of the disease was mitigated by growing citrus scions on rootstock other than sour orange rootstock; it’s particularly susceptible to Tristeza decline. These alternative rootstocks, like Swingle and Carrizo, can get infected by Tristeza decline but exhibit no symptoms. However, many Florida citrus growers have decided to use sour orange rootstock due to citrus greening, meaning Citrus Tristeza Virus has the opportunity for a comeback.
Researchers with the University of Florida Institute of Food and Agricultural Science (UF/IFAS) want to remind Florida citrus growers about the dangers of Citrus Tristeza Virus to keep it from re-emerging, especially since there are many similarities between Tristeza decline and citrus greening, and some incorrect assumptions about the two diseases.
One such assumption is about insect control. Citrus Tristeza Virus is spread by four different aphid species, and neither spray treatments targeting aphids or those targeting the Asian citrus psyllid—the vector that spreads citrus greening—are effective at stopping the spread of Tristeza decline. UF/IFAS researchers are concerned over assumptions that insecticides targeting psyllids will also target aphid, which is not the case.
Furthermore, the two diseases are very similar. Tristeza decline causes “phloem necrosis below the bud union,” per UF/IFAS researchers, reducing sugars that get to the roots. Feeder roots die off; the resulting improper uptake of water and nutrients eventually kills the citrus tree. The symptoms are very similar to those of citrus greening; researchers are concerned growers will not be able to tell the difference.
Lastly, researchers want growers to know that testing has shown that Tristeza decline is still present in Florida, and researchers caution growers against using sour orange rootstock. Growing citrus trees on sour orange rootstock in an attempt to mitigate citrus greening will mean that Tristeza decline could once again become a major pathogen for Florida growers.
This column is sponsored by Griffin Fertilizer Co., and the opinions expressed herein may not reflect those of CFAN or of its advertisers.
BIO: Mike Roberts is the Vice President of the Frostproof, Fla.-based Griffin Fertilizer Co. Roberts joined the company in November 2011. He has spent the majority of his career in the fertilizer/agchem industry. Roberts earned a Bachelor of Science degree in citrus production from Florida Southern College in Lakeland. For more information, visit griffinfertilizer.com.
