EFFECTIVENESS OF ANTIBIOTICS APPLIED AS POSTINOCULATION SPRAYS AGAINST CLOVER PHYLLODY AND ASTER YELLOWS

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Abstract
Oxytetracycline HCl, tetracycline HCl, and doxycycline HCl, applied as foliage sprays to aster (Callistephus chinensis Nees), caused maximum delays in clover phyllody expression at concentrations of 800 ppm. Maximum delays of celery-infecting aster yellows were obtained at 600 ppm with oxytetracycline and at 1,000 ppm, the highest concentration used, with tetracycline and doxycycline. In tests with noncelery-infecting aster yellows, oxytetracycline and tetracycline produced maximum delays at between 600 and 800 ppm, whereas doxycycline proved most effective at 1,000 ppm. Methacycline reached a maximum at 600 ppm but was considerably less effective than were the other three tetracyclines. HCl and amphoteric formulations of oxytetracycline were more effective in delaying clover phyllody symptoms than was the calcium formulation. The HCl formulation was most effective against celery-infecting aster yellows but was followed closely by the amphoteric and calcium formulations. None of the five nontetracycline antibiotics proved effective. Increasing spreader concentrations appeared to decrease the effectiveness of tetracycline HCl.

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