Feb. 3. I9I9 Physoderma Disease of Corn 153 



quantity of infectious material for the following year would be greatly 

 reduced. Where the corn is used for silage or stover, the plants should be 

 cut as near the ground as possible and as early as feasible, in order that a 

 large part of the sporangial material may be removed. Barnyard manure 

 containing these and other corn products should not be used to fertilize 

 corn and should not be put on land where the disease has not been known 

 to occur previously. 



(B) Crop rotation may have a tendency to reduce the amount of injury 

 caused by the disease. The most severe cases known have been on land 

 where corn has been grown continuously for a number of years. In a 

 system of rotation the com plot should be removed as far as possible from 

 the previous plot, as the sporangia of the fungus are wind-borne. Hence, 

 a change of only a short distance in the location of the corn plot probably 

 would have but little effect as a means of reducing the amount of disease 

 present. The longer the duration of the rotation, the better the results 

 are likely to be. 



(C) Where the disease continues to be severe, there is a possibility of 

 selecting disease-free plants and from these obtaining a strain that will 

 be resistant to attacks by the fungus. In order to keep them pure, these 

 plants would have to be selected from pure varieties and grown under 

 conditions where crossing could not take place. It seems hardly possible 

 that a variety will be found which naturally resists the disease, as no 

 indications of such a variety have as yet been seen in the various varietal 

 experiments in the South. 



(D) Control through seed treatment, no doubt, is worthy of little con- 

 sideration because there is slight chance for the sporangia to be seed- 

 borne. However, when seed com is transported from infested territory 

 to territory free from P. zeae-maydis, seed treatment would be a desirable 

 precaution, provided an effective method and means of treatment can 

 be found. Sporangia immersed for 10 minutes in a 4 per cent solution 

 of copper sulphate remained viable. This treatment was used to kill the 

 bacteria on the surface of the sporangia. 



SUMMARY 



(i) The Physoderma disease of corn was discovered in India by Shaw 

 in 1910, and in the State of Illinois by Barrett in 191 1. 



(2) The disease occurs throughout this country as far westward as 

 central Texas and Nebraska and northward to southern Minnesota and 

 New Jersey. It has perhaps almost reached its northern limits, owing 

 to low temperatures, and its western limits, owing to semiarid conditions. 



(3) Considerable damage is caused to corn in the Atlantic and Gulf 

 Coast States and in the Mississippi Valley. The amount of damage 

 varies with weather conditions, moist and warm weather being more 

 favorable for its development. 



98353—19 2 



