396 ALFALFA 



Where the field is generally infected, it will probably be necessary to 

 plow up the field, in which case it should not be put back to alfalfa 

 for at least two or three years. 



Alfalfa leaf spot occasionally gives trouble. Small, dark brown 

 spots appear on the leaves and cause them to drop off. When this 

 disease is abundant, the plant makes a very poor growth. The crop 

 should be cut at once, after which it usually will be free from the 

 disease the rest of that season. 



Root rot is generally used to describe any ordinary decay of the 

 root, although there is a specific disease of this character. The most 

 common root rots are comparable to the rotting of any woody plant 

 which has been injured, allowing ordinary fungous diseases to enter 

 and cause slow decay. 



Insects. Grasshoppers are sometimes injurious, especially to 

 new seeding. This is more likely to be true when alfalfa is sown in 

 the fall, and grasshoppers are likely to migrate in large numbers, as 

 their own natural food supply decreases. 



The alfalfa leaf weevil made its first appearance in this country 

 about 1904. The insect is most injurious to the first crop, when 

 the larva? may appear in large numbers and almost destroy it. The 

 crop should be cut as soon as the larva? appear in large numbers. 

 Then the field should be thoroughly gone over with harrows and brush 

 drags to destroy what insects may be on the ground. This treat- 

 ment not only kills directly many of the larvae, but also strips the 

 stubble of leaves, helping, to starve them. 



QUESTIONS 



1. Where has alfalfa attained greatest importance? 



2. Describe its early history and introduction into the United States. 



3. Describe the climatic requirements of alfalfa. 



4. Does it vary in cold resistance? 



5. Classify the principal types of alfalfa. 



6. Compare common alfalfa with Turkestan, with variegated alfalfa, with 



yellow alfalfa. 



7. Describe alfalfa roots on various yoil types. 



8. Compare the root systems of common, variegated, and yellow alfalfa. 



9. Describe the development of new shoots. 



10. How long does alfalfa live under various conditions? 



11. Give the effect of submerging. Other causes of death. 



12. What are the conditions effecting pollination? 



13. Give soil requirements of alfalfa. Lime requirements. 



14. Fertilizers for alfalfa? 



