One way to ward off Phytophthora is by choosing more resistant or tolerant rootstocks.
HLB bacterium and the root weevil attack all rootstocks. Rootstock tolerance to HLB or Diaprepes depends mostly on ability of rootstock to adapt to soil and water quality conditions in a given grove site.
There’s another stress factor in Florida that appears to top even Phytophthora and root weevil—calcium bicarbonate, manifested in the form of high bicarbonates in well water and soil.
Most wells in Florida are high in calcium bicarbonate because of water management district policies requiring growers to dig deep wells, Graham says.
In HLB-affected groves, it is now advisable to keep roots out of stress by reducing bicarbonates and increasing availability of water and nutrients as needed, he says.
Orange-Co LP, Arcadia, which owns and manages 14,600 acres of citrus, is at the forefront when it comes to combating high bicarbonates and high pH levels in irrigation water and improving citrus root health.
Jerry Newlin, vice president, citrus operations, says he became aware of the positive effect of lower-level pH range and bicarbonates through the work of Graham and Bryan Belcher, production manager at Davis Citrus Management Inc., Avon Park.
Although deep-well water generally is considered good quality from a salinity perspective, it has a fairly high pH level—in the 7.5-8 range—and it has bicarbonates in the range of 180-230 parts per million. Ideally, the pH should be below 7.0 and bicarbs of less than 100 ppm.
Before citrus greening came on the scene, deep-well water was “just fine” for citrus, Newlin says, although golf courses and vegetable growers had been treating their water for a couple of decades.
“Greening obviously causes impairment of the roots,” he says, and that, in turn, adds stress to the tree.
“We found that bicarbonates create a situation where roots can’t get certain elements, such as calcium, potassium, phosphorous and other minor elements,” he says. “By mitigating the bicarbonates and neutralizing the water, you at least make the water no more part of the problem.”
There still could be soil issues from long-term use, however.
Orange-Co now treats its water using enhancements like acidified fertilizer and sulfuric acid.
Finding the right way to treat the problem has been “a real challenge,” Newlin says.