140 Journal of Agricultural Research ' voi. x\^, No. 5 



siderable damage were reported throughout the Southeast and as far 

 north as the Mississippi Valley sections of southern Illinois and Missouri. 

 These areas were usually very limited and were confined for the most 

 part to low, wet lands. Considering the infested area as a whole, how- 

 ever, the percentage of damage, at least in the year 1917, was not very 

 great. 



In 1918, up to July 15, the disease had not developed to any great 

 extent in the South. This fact was due, no doubt, to the very dry season 

 in that section, which will be discussed later. However, mid-July is not 

 too late for considerable injury to develop should conditions so change 

 as to favor the disease. 



FACTORS INFLUENCING THE DEVELOPMENT OF THE DISEASE 



Seemingly the more important factors in the development of the 

 disease are moisture and temperature. The fungus requires considerable 

 moisture, with a fairly high temperature, for a high percentage of germi- 

 nation and infection. If these conditions are realized before the corn 

 plants are more than half -grown, the disease probably will become severe 

 if there is abundant spore material present. The following information 

 regarding these factors has been noted : 



(i) Serious injury has been confined largely to the South, where the 

 summer temperature is continuously high, and to localities in which 

 there has been considerable rainfall during the early growth of the com 

 crop. Plants may become infected in the later stages of growth, but 

 the damage is not likely to be great in cases of this kind. The warm 

 summer showers which may occur daily for a week or more furnish ideal 

 conditions for the development of severe attacks by P. zeae-maydis. For 

 instance, in the coast district of the Carolinas, where the disease was most 

 severe in 191 7, there was considerable rainfall in early summer. This 

 would also hold true for the Delta in Mississippi and for southwestern 

 Tennessee, where there was considerable rainfall in early June. 



(2) Where the seasons were dry the disease was more pronounced on 

 corn growing near water, or on low, wet land where the atmosphere was 

 moist. Plants growing under these conditions are more likely to retain 

 the sheath and bud water until the spores can germinate and produce 

 infection. Conditions of this kind were noticeable at the South Carolina 

 Station in 191 8, where corn on the low bottom lands had considerably 

 more infection than highland corn. In the lowlands the foliage of plants 

 is less subject to drying by winds. 



(3) Where the early corn season was dfy and the late season wet the 

 disease was more severe on late com, and the reverse. Striking exam- 

 ples of the former were noted at the Mississippi Station in 191 7, where 

 there was less than 10 per cent infection on early corn and as high as 40 

 per cent infection on late corn, and at the Kansas Station, where early 

 corn was almost free from the disease, while late corn showed considerable 



