26o DISEASES OF CROP-PLANTS 



Causative fungus. 



Diplodia Zece (Schw.) Lev. {D. maydis Sacc.) Pycnidia black, 

 spherical to pyriform, obtuse or free ; conidia dark brown, 

 cylindrical to elliptical, obtuse, usually slightly curved, one- 

 septate, 20-33 X 5-6 micr. Specific, so far as is known, to corn. 



Two or three species of Fusarium have also been described as 

 producing similar dry rots in the United States. 



Prevention. 



From the nature of the disease, control must depend on the 

 elimination of infected material which can carry over the disease 

 or infect the soil. Rotation of crops is indicated where soil 

 infestation is suspected. 



Root Disease. 



Varying annual losses, sometimes extending to half the 

 crop in certain districts, are attributed to root disease in St. 

 Kitts, Antigua and St. Vincent. The plants show signs of 

 attack when i to 2 feet high, and eventually wilt completely, 

 usually at the time of flowering. If cobs are produced at all they 

 are generally small and misshapen, with little grain. 



The disease or diseases are much in need of investigation. 

 F. W. South reports the presence in St. Kitts material of a 

 Fusarium and also of mycelium resembling that of Marasmius 

 Sacchari on the sugar-cane. The only example seen by the 

 writer, said to be typical of the St. Vincent disease, had the 

 leaves cemented around the base of the stem by mycelium of the 

 latter type. 



Recently T. F. Manns and J. F. Adams have shown that root 

 disease is widely distributed in the United States and that it may 

 be caused by four species of fungi working singly or in com- 

 bination — Diplodia Zece, Fusarium moniliforme, Gibberella sauhi- 

 netii and Cephalosporium Sacchari (the cause of a wilt disease of 

 sugar cane in India and the West Indies). These fungi infect the 

 kernels and are therefore planted in the seed. 



Minor Diseases of Maize. 



The rust Uredo pallida Diet. & Holw, previously known only 

 from Mexico and Central America on the grass Tripsacum lanceo- 

 latum was found on maize in Porto Rico in 1916. It is reported 

 by J. A. Stevenson to attack the older and lower leaves generally 

 at a time when the ears are so nearly mature that little damage 

 can be done. It appears as numerous inconspicuous pale-brown 

 pustules on the under side of the leaves. 



The parasitic Ascomycete Phyllachora graminis (Pers.) Fkl., 

 common on various grasses and sedges, giving rise to rather 

 conspicuous black raised spots on the leaves and leaf-sheaths, is 



