424 PEAS, BEANS, VETCHES, PEANUTS 



variable than the forage crop. Generally when conditions are favor- 

 able for developing a large growth of vine, the seed crop is small, 

 while the best seed crop is ordinarily obtained when the weather is 

 too dry or the soil a little too thin for the best forage crop. Under 

 favorable conditions for a seed crop, twenty to thirty bushels per acre 

 are harvested, but the yield will vary from this all the way down to 

 nothing (Fig. 181). 



Insects and Diseases. Two species of weevil give a great deal 

 of trouble by destroying the stored seed. These weevils lay their 

 eggs on the pods, or when seeds are in storage directly on the 

 seeds. The young larva hatches, finds its way into the seed, and 

 finally matures into an adult in from twenty to thirty days. They 

 continue reproducing until all the peas have been destroyed. The 

 weevil can be destroyed by putting the seed in a tight room where the 

 temperature can be raised to 130 F. for twenty minutes. Also the 

 seed can be put into an air-tight bin and treated with carbon bisul- 

 fide. Carbon bisulfide should be put in a shallow pan and set on 

 top of the seed, when it will quickly vaporize, and being heavier than 

 air, the gas will soon fill all the spaces between the seeds. Two to 

 three pounds of carbon bisulfide are required for each 1000 cubic 

 feet of space. 



The two most common diseases are root knot and wilt. The root 

 knot is caused by a small nematode, and the wilt by a form of 

 fusarium which attacks the roots. No remedy has been found except 

 to grow disease-resistant varieties. 



SOY BEANS 



Soy beans (Figs. 182 and 183) are one of the oldest cultivated 

 plants in eastern Asia, especially in Manchuria and Japan. They 

 are one of the most productive legumes in seed, probably not being 

 exceeded by any other, with the possible exception of field beans. 

 In the Orient they are extensively used for human food, but in this 

 country they have so far been cultivated principally for stock feed. 



Origin and History. A wild plant, closely related to the 

 cultivated soy bean, is found growing throughout Japan and Man- 

 churia, but differing from it in being a trailing vine, while the soy 



