ISHS Acta Horticulturae 235: XIV International Symposium on Fruit Tree Virus Diseases
APPLE DECLINE: CHARACTERIZATION, CAUSE AND CURE |
| Author: | C. Lee Parish |
| Abstract:
A decline condition of apple trees (Malus domestica Borkh.) has been noted in some North Central Washington orchards. The symptoms of decline are small rolled leaves, lack of terminal growth, soon followed by dieback. The disorder appears to originate at one point in the orchard and spread in all directions. Root systems of these trees look generally normal, however there is an absence of small feeder roots. Further testing demonstrated a 100% correlation with a mycoplasma-like organism in the roots of affected trees. Based on this data, oxytetracycline was injected into declining apple trees in the fall. As there was speculation concerning the involvement of Pythium spp. and possibly Phytophthora spp. Ridomil (Metalaxyl) (N-(2,6-dimethyl-phenyl)-N-(methoxyacetyl) alanine methyl ester), a fungicide, was also applied to selected declining trees. The following spring, the oxytetracycline-injected trees exhibited increased feeder root growth and improved shoot growth. The incidence of mycoplasma-like organisms declined significantly after oxytetracycline injections. Ridomil had no effect on apple decline trees. It is concluded the causal agent of apple decline is a mycoplasma-like organism. | |
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