PRINCIPLES IN USING FUNGICIDES 



309 



also be varied by using a little more or a little less of the lime and 

 sulfur in the 50 gallons of water. As a winter spray one or two 

 pounds of copper sulfate is sometimes added to the 50 gallons of 

 lime-sulfur. This is of special value against apple rust. 



The use of poisons with a winter or summer spray of lime-sulfur 

 is effective against chewing insects. 



Principles in Using Fungicides. — It is important to remember 

 that all fungicides should be used before the disease breaks out. 

 After a serious outbreak little effect can be seen from spraying 

 (Fig. 217). Plants that have not yet been affected may usually 

 be protected by spraying after neighboring plants are diseased. 

 Use as strong a spray material as possible without injury to the 



Fig. 217. — Apple scab is prevented by use of lime-sulfur as a winter spray, by the sum- 

 mer strength of lime-sulfur when the petals fall, and the same two weeks later. 



plants. Remember that young, succulent plants are more tender, 

 and weaker solutions are necessary. A little trial will help to 

 determine this point without depending absolutely upon formulas 

 given in books or bulletins. 



The principle involved in the use of fungicides is to use a mate- 

 rial which is as permanent as possible without destroying the plant 

 or any of its product, or to make it unfit for human use. 



The spray must be strong enough and frequent enough to kill 

 the spores of the disease before they enter the tissues of the plants. 

 After they obtain a good foothold it is difficult to control their 

 growth. 



Special directions for fighting the different diseases are men- 

 tioned in the discussion of the different fruits and vegetable crops. 



