7 



Both the wilt disease of okra and that of cotton are sometimes com- 

 plicated by the presence in the field of the root nematode, Heterodera 

 radicicola. The combined attack of these two parasites results in some- 

 what greater injury to the plants than would be caused by either one 

 alone. This is particularly true of okra, which suffers considerably 

 more from the attacks of the nematodes than cotton growing- beside 

 it. It is not believed by the writer, however, that the assistance 

 of the root nematodes or of any fungus is necessary to allow the 

 wilt fungus to gain entrance to the roots of cotton. Some of the 

 worst cases of wilt disease that have been observed were on land 

 where no root nematodes could be found. Nor is it believed that 

 mechanical injury to the roots from cultivation or other causes is 

 necessary to produce infection. Cotton planted on infected fields 

 late in the season, after cultivation had ceased, and when conditions 

 were not favorable to the growth of damping-off fungi in the soil, 

 contracted the disease at the usual time. The indications are that 

 the fungus is a sufficiently aggressive parasite to make its way unaided 

 into the vascular system of the plant whenever the plant is liable to 

 infection. 



The progress of the disease is always slow as compared with that of 

 other plant diseases. The period of incubation, or the time elapsing 

 after the young seedling is exposed to the attacks of the fungus and 

 before the disease becomes manifest, is usually at least forty days and 

 often much longer. Much depends onthe individual plant itself. The 

 conditions which favor the progress of the fungus through the plant 

 are not fully understood, but from some observations that have been 

 made it is l:>elieved that highly fertilized plants, growing vigorously, 

 succumb more readily than those which have grown on poorer soil. 



In the early history of the wilt disease the cause was supposed by 

 the planters to be the excessive applications or injudicious use of 

 conunercial fertilizers, and many of tlie leading planters in the Sea 

 Islands made careful experiments with various modifications of their 

 fertilizers, such as the use of marl, salt mud, kainit, and lime, and 

 the increase oi- decrease of the proportions of phosphoric acid and 

 potash. Mr. W. G. llinson, of James Island, South Carolina, a very 

 successful planter, has informed the writer that the result of all these 

 trials has been to convince those who made them that the disease 

 can not be controlled by any changes in their system of fertilizing. 



The wilt disease occurs in so many widely separated localities and 

 under such varied cultural conditions that it is not probable that any 

 errors in tlie agricultural practice are the primary cause of tlie trou- 

 ble, although the planting of cotton year after year on the same land 

 and tlie common practice of plowing under the last year's stems in 

 preparing the ground in the spring ])()th t(!nd to hasten the spread of 

 the wilt fungus after it has once been introduced. 



