Phytophthora and leprosis diseases can each substantially reduce productivity of a citrus tree, but when they attack trees already weakened by HLB, the result can be fatal.
Ozgur Batuman, assistant professor at the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS), explained how co-infection impacts HLB-infected trees during a recent UF/IFAS webinar.
Phytophthora species are soil-borne fungal pathogens found worldwide that attack the root systems, trunks and fruit of citrus trees at any age.
Diseases caused by Phytophthora species include brown rot, foot rot, crown rot and root rot. Brown rot can directly reduce yields of early-maturing varieties and can delay harvest of fresh market fruit or risk packinghouse rejection of the load because it can spread post-harvest. Foot root and crown rot can kill trees but are uncommon when the correct rootstock is chosen. Root rot can reduce tree vigor and fruit production.
According to Batuman, all of these diseases have been manageable in the past. However, management is complicated by HLB.
As the cycles of root production and disease become disrupted and fluctuate widely due to phytophthora and HLB infection, proper timing of fungicide applications become more complicated.
“In this case, improving fungicide timing, number and applications of rates are needed to achieve better control,” Batuman says.
While citrus leprosis is not currently present in Florida, it is considered one of the most important emerging citrus diseases in other parts of the world.
Currently, the disease is widespread in South and Central America, including Mexico. The disease is transmitted by false spider mites, which are present in Florida. The combination of the existence of the disease vectors in Florida and the presence of the virus in nearby production areas makes it a potential threat to the Florida citrus industry.
Citrus trees with leprosis have necrotic lesions, often with a yellow halo, on the leaf, bark (stem and trunk) and fruit at the feeding sites of the mites. The fruit lesions are usually pale in color at first and then may become dead in the center with a distinct yellow halo.
Given that Florida’s climatic conditions are highly suited for establishment of citrus leprosis, Batuman says that monitoring groves and early detection are essential to reduce the spread of the disease and aid in eradication efforts, should this disease enter Florida.
If you suspect leprosis symptoms, contact your local Extension agent or the Florida Department of Agriculture and Consumer Services Division of Plant Industry.
This article was written by Ashley Robinson, multimedia journalist for AgNet Media in Gainesville, Florida.