DISEASES OF CULTIVATED PLANTS 551 



These leaves are usually left on the field. Even where they are most 

 carefully raked up and burned large numbers of oospores must still 

 remain in small broken pieces of leaves which cannot be removed. 

 The raking and burning of the tops is to be strongly recommended, 

 as in this way a large part of the resting spores are destroyed. The 

 practice of throwing tops and decaying bulbs back on the field or on 

 manure piles cannot be too strongly condemned. (N. Y. [Cornell] 

 E. S. B. 218.) 



Fusarium Blight. This is often serious on young onions in, 

 old soil and is the forerunner of heavy losses from soft rot in storage. 



Downy Mildew (Peronospora Schleideniana) . This is likely to 

 occur upon onions, although it has not been seen in Ohio by the 

 writer. The treatment would be as for downy mildew of other 

 plants. 



Dry or Black Neck-Rot. This is the most serious disease of 

 white onions in Ohio since the losses are so very large from it, par- 

 ticularly in Hardin County. The white onions are grown for some- 

 what special markets and it is the custom, at present, to gather early 

 before the tops fall over, to top at once, and put up in crates in order 

 to preserve the white color of the onion. As a rule this is not practiced 

 with black, red and yellow sorts, so that this neck or dry-rot is not so 

 common with them. Preliminary investigations have been made of 

 this trouble and it appears to be clearly different from the smudge 

 fungus which also disfigures the exterior of white onions. The fun- 

 gus of dry-rot or black-neck (Sclerotium cepivorum) requires further 

 investigation. In Ohio onion districts the losses are very serious be- 

 tween the gathering of the white onions and time for winter storage 

 while the crates are piled in buildings or in covered ricks in fields. 



It appears at this time that the early topping of the white onions, 

 leaving a green neck, offers an inviting way for the disease to enter; 

 that the invasion in this direction appears from the sclerotia of the 

 fungus which forms in this region. The disease appear* to grow 

 worse with continuous cropping of onions and the losses have re- 

 cently been so large in storage as to render storage of white onions 

 unprofitable. It has been suggested by this department that the 

 white onions should be gathered and ricked in crates at once, either 

 in buildings or covered with tent or temporary enclosure of building 

 paper and disinfected or treated with formaldehyde gas as per the 

 spray calendar. (See formula elsewhere.) The enclosure should 

 not be opened for 24 to 48 hours after treatment. In this manner 

 it is hoped to keep down the infection of the white onions as well as 

 of any others from similar troubles. 



Heart-Rot. This disease has been under investigation and ap- 

 pears to come in all varieties of onions, following the topping, by its 

 rapid invasion of the center of the bulb through bacterial infection. 

 It should be controlled by attention to disinfection of the topping 

 machine or to similar treatment to that recommended for dry-rot. 

 This disease ends in the complete destruction of the bulbs through a 

 soft rot different from that described under soft-rot. 



