Johnson
University of Florida Institute of Food and Agricultural Sciences plant pathologist Evan Johnson tells how drastically HLB harms citrus tree roots and suggests some ways to prolong root longevity and improve tree health.
“It (HLB) causes very substantial root loss, up to between 30 and 50 percent early in the disease process from before visual symptoms are present to early symptom development,” Johnson says. “And then it continues to 70 to 80 percent root loss later in the infection. Unfortunately, that’s where most trees in Florida are at the moment.”
Johnson suggests doing all possible to improve root longevity “so that the roots are functional for the tree for a longer period of time, which mainly involves reducing the stresses on the root system … We find that one of the best ways to improve root longevity is (to) reduce environmental stresses such as drainage issues and flooding, pH/rootstock incompatibilities, things like that, where the soil and the rootstock don’t match.”
Reducing other pathogens and pests also helps. “Where possible and economically feasible, depending on what pests and pathogens you have in the soils, you need to manage those as well, because they can be a major detriment to the tree on top of HLB,” Johnson says. “HLB actually makes some of them worse, like phytophthora and diaprepes.”
Another key is matching the rootstock to the soil. “If the rootstock is matched to the soil type, we see a much better early development of that tree,” Johnson says. “It grows much faster; it gets into production much faster and will be healthier throughout its life … It avoids later expenses where you would be putting inputs in to try to mitigate the mismatch between the rootstock and the soil. If you start with a rootstock that matches that soil, it eliminates that extra cost later on.”
In summary, Johnson emphasizes the importance of managing individual sites based on their characteristics. “You need to manage the root health based on the properties of the site itself,” he says. “You need to know the soil at the site, you need to know your rootstock at the site and you need to know the pest and pathogen problems of that site. And do the management based on the site … It has to be block-by-block focused.”
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