In-place elimination of HLB-infected trees through application of phytotoxic chemicals

Resumen

Current recommendations for dealing with huanglongbing (HLB) affected trees call for scouting four times per year and clipping or chain-sawing the trunk (stumping) for removal of the infected trees as soon as possible after each scouting. Tree removal is labor intensive, costly, and diffi cult to schedule during the harvest season. An alternative method would be to kill the infected trees in-place and remove them at a convenient time and not more than once per year. Experiments were conducted to determine the effectiveness of herbicides and their method of application for killing mature citrus trees in situ. Canopy sprays that included Remedy (trichlorpyr) were effective, but Landmaster II (glyphosate + 2,4-D) did not kill the trees, but both resulted in canopy damage to adjacent trees. Spraying the inside canopy from under the tree was effective if the spray covered the more distal growth towards the row middle. Again, Remedy was more effective than Landmaster II. Cutting four sides of the trunk with 10 cuts from a hand hatchet and spraying the cuts with concentrated herbicide worked well with Arsenal (imazapyr) or Clearstand (imazapyr + metsulfuron methyl), but Remedy, Landmaster II, and 2,4-D alone were not very effective. Commercialization of this method will probably require a vehicle-mounted attachment to make the cuts and spray the chemical. Tests were also conducted with soil injection of the fumigant Midas (iodomethane). This procedure worked fairly well on small to medium size trees, but further testing is needed to increase consistent tree kill on large trees. Successful application of the trunk herbicide or soil fumigant method should be a cost-effective replacement for stumping HLB affected trees, but these chemicals are not cleared for use in citrus and require pesticide use labels.