122 THE PESTS OF CULTIVATED PLANTS 



be controlled easier than certain others, but relief can be 

 had from many pests by following good cultural methods. 



Crop rotation is an important factor in controlling some 

 of our plant troubles. Rotation is beneficial in combating 

 those insects and diseases that remain in the soil over winter 

 and which are not killed by the cold weather. Besides insects 

 there are many diseases which are found in the soil and that 

 will grow on one class of plants but will not attack other 

 classes. These diseases therefore can be killed out by the 

 growing of a different crop on that land. For this class of 

 diseases it is never advisable to grow the same kind of a crop 

 on a piece of land any two years in succession. By rotating 

 the crops we not only control many insects and diseases but 

 we improve the general condition of the soil as well. 



Fall plowing is valuable in destroying some insects. Many 

 insects pass part of their life history in the ground. These 

 insects make small burrows or homes in which they spend 

 the winter. If they are allowed to remain undisturbed they 

 will live through the cold weather, but if the soil is plowed 

 up in the fall and the insects exposed to the cold, a great 

 many of them are killed. This same treatment is valuable in 

 destroying the eggs of many other insects that lay them in 

 the ground. When the eggs are exposed to the winter weather 

 they are also killed. 



REVIEW QUESTIONS. 



1. Describe the four classes of pests that attack plants. 



2. Is the damage done to plants by these pests large or small? 



3. Into what three classes are the insects divided? 



4. What is complete and incomplete metamorphosis? 



5. Give the four stages in complete metamorphosis. 



6. Give the three stages in incomplete metamorphosis. 



7. How does an insect with incomplete metamorphosis grow? 



8. Name and describe the three divisions into which plant diseases are 

 divided. 



9. Discuss some of the symptoms of a diseased plant. 



10. Discuss bacterial and fungous diseases. 



11. Name and describe the three classes of bacteria. 



12. How do bacteria multiply? 



13. Discuss the injury to plants due to predaceous animals. 



14. Discuss physiological troubles of plants. 



15. How can physiological troubles be controlled? 



16. Discuss the means of control for insects and diseases. 



17. Describe several devices for the control of predaceous animals. 



18. What is meant by cultural control measures for plant pests? 



