ASTER YELLOWS

plant disease once thought to be caused by a virus but now believed to be of mycoplasmal (bacterial) origin. It is found over much of the world wherever air temperatures do not persist much above 90 F (32 C). A wide range of species of plants are susceptible, including many wild and cultivated plants, both vegetables and garden plants. Typical symptoms include yellowing (chlorosis) of young shoots, stiff and erect bunchy growth, greenish and distorted or dwarfed flowers, and general stunting or dwarfing. Leafhopper insects serve as transmitting agents when they feed on an infected plant and then on a healthy one. No transmission occurs through leafhopper eggs or plant seed. The mycoplasma is perpetuated in overwintering weed and crop plants, in propagative parts (bulbs, corms, tubers), and in leafhoppers in mild climates. The mycoplasma is destroyed in plants and leafhoppers subjected to temperatures of 100 to 108 F (38 to 42 C) for two to three weeks; thus, aster yellows is rare or unknown in many tropical regions. Control is effected chiefly by excluding the leafhopper carriers, by promptly removing diseased crop and weed plants as well as all overwintering susceptible weeds, and by spraying or dusting with a contact insecticide. Oxytetracycline antibiotics effect remission of symptoms in new growth.