DISEASES IN GREENHOUSE 95 



overwatering, since transpiration and 

 evaporation are then very active. What 

 is true of "damping off" and the mildews 

 is also true for root knot. The minute eel 

 worms cannot thrive unless there is suiBB- 

 cient moisture in the soil. Neither can 

 they thrive in soils that are flooded, since 

 they must have air to live. This is taken 

 advantage of in open fields where root 

 knot is controlled by flooding the land. 

 Overwatering, or any form of injudicious 

 watering, is no doubt an important factor 

 in predisposing the sweet pea plants to the 

 attacks of Thielavia, Rhizoctonia, Chae- 

 tomium, and Fusarium root rots. It is 

 therefore well to provide some means of 

 drainage, especially where the beds are 

 solid and in the ground. It is a good 

 practice to lay at the bottom of the beds 

 from one-half to one foot of ashes or a 

 layer of broken bricks or crushed stones. 



