The two most important symptoms of the corn disease caused by Diplodia zeae are seedling blight and ear rot.

Artificial inoculation of the ears was effected in all stages of their development but most readily in the milk stage. Infection of seedlings from Diplodia-infected kernels usually takes place in the natural wounds at the points of production of the secondary radicles near the attachment of the mesocotyl to the scutellum.

Field experiments showed that Diplodia-infected seed in 1925 and 1927 produced 4.5 and 1.3 times as many weak plants, respectively, as did nearly disease-free seed.

Plants that are weak due to Diplodia zeae and Basisporium gallarum early in the season often produce normal ears if there is no competition in the hill but seldom produce normal ears if there is competition with strong plants.

The visible-root sand culture method, devised as a means of following the spread of Diplodia in the underground parts of the corn seedling, has been found of value in correlating micro-organism injury or disinfectant injury with top growth and in determining the effect of moisture and temperature on the development of Diplodia seedling blight.

Fewer plants developed from Diplodia-infected seed at 15 °-19° C. than at 20°-24° C. There was less visible seedling blight at the lower temperature, due to the large number of seedlings that were killed before they reached the surface of the soil.

Results of seed treatment experiments in 1926 using nine mercury disinfectants on nearly disease-free seed, showed that yields were not increased or decreased significantly. However, in 1927, treated, high quality, selected seed corn entered in the state yield contest gave significant increases. In 1926, Diplodia-infected treated seed showed significant increases ranging from 6.8 to 13.9 bushels per acre. The yield from the highest yielding, Diplodiainfected, treated seed was within about six bushels of that from the nearly disease-free seed. In 1927, three mercury dust disinfectants (Bayer Dust, Merko and Semesan Jr.) increased the yield of Diplodia-infected seed from 21.3 to 30.2 percent and of Basisporium-infected seed from 15.5 to 19.6 percent.

The benefits derived from treatment of seed corn vary greatly with the amount of infection in the seed, with the climatic and soil conditions at planting time and apparently with the strain of corn used.