62 BULLETIN 416, U. S. DEPARTMENT OF AGRICULTURE. 



tionable to the farmer, since in ordinary seasons it results in a reduc- 

 tion of the yield, and because of the fact that it suffers heavily in the 

 event of the appearance in the late summer of the bollworm, or the 

 leafworm, or of the boll weevil in western sections. 



We have made an effort to establish the rotational value of the 

 common crop plants, garden plants, and field plants, both by planting 

 them in or near infested fields and by making frequent examinations 

 of a great many of these plants which happened to be planted by others 

 in infested localities. Besides cotton, we have found red spiders 

 commonly upon the followmg field crops: Cowpeas, vetch, red and 

 white clover, alfalfa, corn, hops, beets, and watermelon. They also 

 have been found frequently upon the following garden crops: Pea, 

 bean, onion, tomato, pepper, Irish potato, sweet potato, lettuce, 

 okra, turnip, mustard, radish, cabbage, squash, beet, celery, straw- 

 berry, and several others. Our host list also included many of the 

 common bush fruits, tree fruits, and dooryard plants. Rather acute 

 cases have been seen on com, cowpeas, and sweet potatoes. The 

 only plants which have appeared largely immune are the grasses 

 and the small grains. Owing probably to the lack of shelter, which 

 the foliage of the grasses exhibits, the mites are unable to maintain 

 themselves under severe weather conditions. The planting of grains 

 on land normally heavily infested is therefore a measure which 

 should be considered by the farmer. 



, REPRESSIVE. 



That it is possible to eradicate the pest from infested fields has 

 been demonstrated, but in many cases the task is so tedious that 

 only the most determined farmers will resort to the necessary meas- 

 ures. 



The experiment has been tested frequently of pulling up and 

 destroying the first few plants which show infestation. In applying 

 this measure the farmer must maintain a constant surveillance of 

 suspected fields, so that the earliest affected stalks may be detected. 

 In such cases the operation will probably have to be repeated several 

 times, owing to the fact that certain plants are overlooked during the 

 first examination because the colonies on them are too yoimg to 

 have revealed their presence. Great care should be observed in 

 locating every plant which shows the characteristic red spots, and 

 these must be carefully taken from the field and burned. This 

 must be done before mfestation has reached the point where there 

 is danger of a secondary dissemination, and before there is liability 

 of the dropping of infested leaves. 



If infestation has spread until a considerable area has become 

 involved, more drastic steps will have to be taken. It is sometimes 

 advisable, where a continuous area of infestation occurs in a large 



