Diseases Caused by Phytoplasmas

Symptoms of diseases caused by mycoplasmalike organisms include stunted growth, chlorotic or reddened leaves, leafroll, reduced numbers of subterranean tubers, sexual bud elongation, and the production of aerial tubers. Some plants exhibit witches'-broom symptoms, i.e., the proliferation of many small shoots and leaves. Symptoms may be confused with damage caused by psyllid insects and, in some cases, with leafroll virus.

These diseases are uncommon in California. Beet leafhopper transmitted virescence agent is transmitted by the beet leafhopper , Circulifer tenellus; western aster yellows is transmitted by another leafhopper, Macrosteles fascifrons. Both mycoplasmalike organisms occur in other herbaceous plants. The incidence of the disease is dependent on the abundance of the leafhopper vectors and the reservoir of the mycoplasmalike organisms.

Although these diseases rarely cause economic damage in California, they are often found in fields with weedy edges or with weedy areas nearby. Controlling weeds near potato fields helps to prevent development of these diseases.