Vulnerability of citrus trees to phytophthora root rot is a concern for cold-hardy growers. But there are precautions that producers can implement that will guard against infection buildup.
One of those precautions includes site selection and not planting trees in poorly drained locations, according to Jonathan Oliver, University of Georgia assistant professor and small fruits pathologist.
“Site prep is really important with respect to phytophthora, so preventing issues is the best way to keep from having major problems with phytophthora,” Oliver said. “Once the disease is present, yes, there are fungicides that can be used, but it is better to not have the problem in the first place.
“If water stands after a rainfall in a location, it might not be a good place to put trees. There may be some things that can be done to improve drainage at the location before trees are put in. But once trees are in the ground, there’s not much that can be done to improve the drainage situation.”
There are three types of phytophthora diseases that affect citrus. The types are described based on where the damage is located. Phytophthora root rot causes damage to the fibrous or feeder roots. Phytophthora foot rot affects the trunk bark, and phytophthora brown rot causes lesions on fruit.
Root rot infections typically occur in poorly drained areas or areas that have received too much moisture. Damage can result in death of young and mature trees.
“Phytophthora needs water to reproduce and spread,” Oliver added. “However, the damage that it causes to the roots make the plant more vulnerable to drought stress. If the plant only has half or a third of the root system that it’s supposed to have, once dry spells or heat spells come, and the tree needs to move a lot of water through the tree, it just doesn’t have the roots to take that up. You can actually see trees crash as a result.”
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