60 BULLETIN 416^ V. S. DEPARTMENT OF AGRICULTURE. 



eign vegetation remained free of red spiders, while the neglected 

 portion developed serious infestation. Too much emphasis can not 

 be placed on the importance of riddmg all field borders, ditch banks, 

 terraces, etc., of all vegetation so far as possible. Pokeweed and 

 other persistent perennials should be grubbed out. 



The destruction of weeds by spraying with sodium arsenite at the 

 rate of 1 pomid to 20 gallons of water is very effective. 



Many cases of infestation in urban locahties can be traced back to 

 borders of cultivated violets growing in near-by house yards. (PI. 

 VII.) In several instances of past severe amiual hifestation violets 

 adjoining fields have been thoroughl}^ sprayed, with the result that 

 no red spiders appeared m these fields. The objection to this treat- 

 ment is the failure on the part of the average person to persevere 

 with the spraying until the mites have been entirely exterminated. 

 The most satisfactory procedure consists in the removal and destruc- 

 tion of the violets. 



Early in the investigation it appeared possible that there might 

 be a variation in the degree of susceptibihty of cotton varieties to the 

 red spider, for in 1903 Watt and Mann stated that there was a marked 

 difference m the susceptibility of tea (Thea) varieties in India to 

 the Indian red spider, Tetranychus hioculatus Green. 



During 1912, 1913, and 1914 many varieties of cotton have been 

 planted in exposed fields and records have been made of the per- 

 centage of infestation developing in each. Parallehng these experi- 

 ments data have also been gathered from many cases of infestation m 

 South CaroUna and North Carolma. In Table XXVII, which repre- 

 sents the relative degree of infestation of the varieties tested at 

 Batesburg, the position of each variety is obtamed by averagmg the 

 infestation percentage as exhibited by it during the several years; thus, 

 variety No. 1 was the heaviest infested and No. 37 was the lightest. 



Table XXVI. — List of standard varieties of cotton, tested for susceptibility to red-spider 



injury, Batesburg, S. C. 



1. Lone Star. j 20. Dixie. 



2. Keenan. I 21. ClevelaiKl. 



3. Christopher. 



4. Bank Account. 



5. Rublee. 



6. Money ]\Iaker. 



7. Cook's Improved. 



8. Simpkins. 



9. Uncle Sam. 



10. Broadwell. 



11. Stone's. 



12. Toole. 



13. Covington-Toole. 



14. Hawkins. 



15. Mebane Triumph. 



16. Lowe. 



17. Culpepper. 



18. Peterkin. 



19. Excelsior. 



22. World's Wonder. 



23. Russell Big Boll. 



24. Hite's Prolific. 



25. Bostwick. 



26. King. 



27. Columbia L. S. 



28. Poor Land. 



29. Bates. 



30. Rowden. 



31. Truitt. 



32. Trice. 



33. Shine's Early. 



34. Sea Island. 



35. Wade's Triumph. 



36. Dongola. 



37. Summerour's Half and Half. 



