PLANT DISEASES AND THEIR TREATMENT 211 



becomes diseased. The plants begin to look sickly, wilt, and 

 die. This is called flax wilt. It can be controlled by prac- 

 ticing a rotation and by spraying the seed until moist with 

 formalin at the rate of one pound of formalin to forty-five 

 gallons of water. 



Cow-peas grown continuously on the same piece of ground 

 are also often attacked by a wilt. It is controlled by rotation 

 and planting varieties which are not easily effected by the 

 disease. 



5. Rot. — Many plants are attacked by diseases which are 

 called "rot." There are several forms of rot and each would 

 have to be described separately. Some of the worst forms are 

 the bitter rot of apples, two or three kinds of rot which attack 

 grapes, and the tomato rot. In a general way these can be 

 controlled by the use of Bordeaux mixture, and by picking, 

 and destroying all fruit beginning to decay. 



6. Scab. — Scab is a disease indicated by rough and knotty 

 places on the skins of the fruit. In the case of potato scab, it 

 gives the potato the appearance of having been chewed by an 

 insect. For the scab on apples and pears it is well to spray 

 with Bordeaux mixture several times during the season, begin- 

 ning early in spring before the buds open. Potato scab is 

 controlled, first, by planting in a new field each year, and, 

 secondly, by soaking the tubers in a solution of formalin made 

 by using one pound of formalin to thirty gallons of water. 

 The potatoes should be soaked two hours in this solution be- 

 fore planting. 



Bordeaux Mixture. — This mixture is made as follows: 

 Dissolve four pounds of copper sulphate in hot water. Then 

 slake four pounds of lime in a separate vessel and add water 

 until it is like milk. Strain the lime through a sieve to re- 



