346 Diseases of Economic Plants 



three or four years old, still of satisfactory viability, is free 

 from infection. Crops should be rotated and seed bred on 

 isolated clean plats. Treatment with commercial sulfuric 

 acid to remove the lint and kill the spores has given some 

 success. Hot-water seed treatments are also beneficial 

 against this and other cotton, seed-borne diseases. The 

 temperature should be kept as nearly 65° C. (149° F.) as 

 possible for fifteen minutes. Different varieties of cotton 

 show different resistances to heat and their germination 

 should be tested after treatment. 



Boll-rot "'^'' {Diplodia gossypina Cke.). — This is chiefly a 

 black-rot of the bolls, which are thickly studded with pyc- 

 nidia. These exude such quantities of black spores as to 

 appear smutty. The entire contents of the boll also turns 

 black. Similar effects are less common on the stem. The 

 disease is cause of considerable loss in Louisiana. Fusarium 

 boll-rot (Fusarium sps.). — This usually follows injury of 

 some kind and the fungus is really a saprophyte. Other boll- 

 rots are produced by Rhinotrichum, Volutella, Sclerotium, 

 Olpitrichum, Botryosphseria, and even by the gill fungus 

 Schizophyllum. 



Texas root-rot "^ ^'' ^"-' ^^^ (Ozonium omnivoruvi Sh.). — 

 The first technical description of this disease was given by 

 Pammel in 1888. It has since been the subject of many 

 papers, and is known to occur in very destructive form in 

 Texas, Oklahoma, New Mexico, and Arizona, though it has 

 not been seen east of Texas. The estimated loss from this 

 root-rot in 1906 in Texas was about $3,000,000. Some 

 planters regard it as a worse enemy than the boll weevil. 



In this disease a few of the plants may wilt and dry up 

 in a day. Later, many plants suffer a similar fate, resulting, in 

 irregular spots of disease in the field, marked by the presence 

 of numerous standing, dead plants. The plants succumb with 

 marked rapidity on hot days following rain, not so rapidly in 

 continuous dry weather. Especially after a rain, living 

 plants surrounded by dead ones may show symptoms of the 

 disease in the form of dense sterile mycelium upon the tap 



