Phytophthora root rot’s impact on young citrus trees is concerning for groves in the cold-hardy citrus region of North Florida, South Georgia and South Alabama.
Newly planted trees are more vulnerable to the disease than older, established trees, says Jonathan Oliver, University of Georgia assistant professor and small fruits pathologist. He discussed the disease’s impact during the Citrus Grower’s Summer Update last month in Valdosta, Georgia.
“Younger trees are more vulnerable because they start out with a smaller root system. They’re small trees, and the phytophthora root rot will cause the roots to rot and be damaged. They’ll lose their root mass, and if it takes out part of the root system, those trees will be stunted,” Oliver explained. “They won’t grow as well. They won’t grow out the roots like they should in order to be ready for when stress occurs like dry spells and warm spells.”
Because older trees are more established and have a stronger root system, they can better withstand the disease.
Phytophthora infection usually occurs in low, poorly drained areas or in areas that have received too much irrigation or rainfall. Cultural controls include ensuring adequate drainage and proper irrigation practices. Chemical control options include fungicides applied at regular intervals coinciding with periods of root flushes. Young trees require preventive applications.
“It is more of a problem than we had realized. We have seen younger citrus trees die in some locations as a result of phytophthora root rot, especially on the younger groves (1 to 3 years old) that are being put in,” Oliver said. “It’s why I’m recommending routine fungicide applications on a regular basis through the first couple of years after planting in Georgia.
“We don’t have a lot of older, mature groves, but we definitely have seen isolated cases of older trees dying as well from phytophthora. It is an issue that growers need to be aware of and deal with.”
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