PRELIMINARY STUDIES OF ROOT AND BASAL STALK ROT OF MATURING CORN IN ONTARIO

Abstract

In Ontario, basal stalk rot of corn occurs in the autumn and is of major importance, whereas bacterial stalk rot is of no economic significance. The latter disease, which results from stomatal penetration by Erwinia dissolvens, may occur on a few susceptible corn plants in early July during extremely hot humid weather, although ordinarily temperatures are sufficiently low in the province to limit its development. Common basal stalk rot of corn is usually initiated by the spread of organisms from diseased corn roots up into the stalks; rotting may begin also in tunnels produced by corn borers. Diplodia zeae and Gibberella zeae, the two pathogens that are responsible for most of the stalk rotting in the central part of the American corn belt, were of no practical importance during the last two years. Bacteria, Pythium arrhenomanes, and Fusarium moniliforme were commonly found in the necrotic part of the corn stalk. Diseased plants begin to appear in mid-August and daily become more numerous until the first killing frost occurs or the plants become senescent. The leaves suddenly droop and wither, and are dead within four or five days after the first symptoms appear. By this time, the basal part of the stalk is necrotic and at least some of the roots are decayed. Pith tissues are destroyed and the stalk frequently breaks over near the ground level. All stalk rot pathogens finally produce the same syndrome. P. arrhenomanes causes a root necrosis at first which later spreads up into the stalk and, in Ontario, is of major importance in the corn stalk rot disease. Pratylenchus pratensis has been found in corn roots but its importance is unknown.