39 



treated would be small and the expense insignificant. Numerous 

 experiments made at this Station for some years, as well as those 

 made by Atkinson,* have shown that sterilization of the soil is a pos- 

 itive remedy for this trouble. In some experiments made by us it 

 was found that, where pots of soil had been treated by steam heat 

 sufficient to reach a temperature of 140° F., no Damping off took 

 place, while it occurred in those pots which had been heated to only 

 127° F. We consider it worth while to plant seeds in sterilized 

 soil regardless of the Damping off fungus, since the increase in 

 the per cent of germination and the accelerated growth of the seed- 

 lings amounts to considerable. 



Powdery Mildew. 



(Erysiphe Polygoni, DC.) 

 This is the most common Mildew occurring on cucumbers and the 

 one with which practical men are most familiar. It does not, how- 

 ever, usually occur in sufficient abundance to cause very much dam- 

 age if proper precautions are followed. It appears as a whitish 

 growth on the upper surface of the older leaves, usually confines 

 itself to small areas, and if the conditions are favorable for it to 

 spread it will completely cover the leaves and eventually affect the 

 whole crop. The most favorable conditions for Mildew infection are 

 lack of light and ventilation, too much moisture, and too high tem- 

 perature. These conditions produce plants of inferior texture and 

 resistant properties which render them more susceptible. This Mil- 

 dew has never occurred in our house except as it has been purposely 

 introduced, and when certain plants have been infected intentionally 

 one season there never has been any indication of its reappearing 

 the following year. We have endeavored a number of times to 

 induce Mildew to grow on our crops, but only succeeded once in 

 getting a good growth. When certain plants were inocculated, only 

 a slight growth would occur which showed no tendency to spread. 

 In order to obtain much infection it was necessary to cover some of 

 the plants with glass and darken them with opaque paper, thus pro- 

 ducing a condition of moisture and shade which was desirable. On 

 one occasion when the Mildew had been quite well established on 

 one or two plants it quickly spread over the whole house and affected 



•Cornell University, Agricultural Experiment Station, Bull, 94, 1895. 



