62 KOOT-KNOT AND ITS CONTROL. 



when the plants had grown long enough so that the first nematodes 

 that entered the roots were not yet mature but were in the nonmotile 

 stage they were plowed up and either removed and destroyed or 

 turned under ^dth the tops do\vn and roots up. The plants treated 

 in the latter manner died quickly and the nematodes in the exposed 

 roots died within a few hours. By repeating this process several 

 times (three to five) in a season the number of nematodes was found 

 to be so reduced that good crops could be growm again for several 

 years. In using tliis method extreme care must be taken to plow 

 imder or remove the plants at the right time, for if left too long the 

 nematodes ^^ill reach maturity in the roots and lay eggs, thus increas- 

 ing instead of diminisliing the number of nematodes in the soil. 



Frank ^ and others have also recommended this method for com- 

 bating the root-knot nematodes. The wTiter has found no record of 

 any such experiment having been tried. He made experiments on this 

 Ime two different years at Monetta, S. C, but with no success. A 

 badly infested field was separated from adjacent plats by a shallow 

 ditch, 2 feet wide. The plat was sowti very thickly to Whippoorwill 

 cowpeas, a variety susceptible to root-knot. Roots from numerous 

 plants were examined microscopically at short intervals to determine 

 the stage at which the nematodes first entering the roots had become 

 motionless and were approaching sexual maturity. At that stage 

 the plants were destroyed, on one plat by plowing them under, on 

 another by loosening the roots and removing and destroying the 

 plants, roots and all. The time necessary to reach that stage was 

 found to be from 19 to 21 days after the so\\'ing of the seed. As soon 

 as the trap crop was removed or turned under, the soil was made ready 

 and resown wdth cowpeas, the process being repeated. This was done 

 until four or five crops of cowpeas had been removed in this manner. 

 The next year through these plats and the check plat were planted 

 rows of tomatoes, beans, okra, and New Era cowpeas. Some of these 

 plants remained free, while some were slightly affected and some 

 very badly affected by root-knot, no difference being noticeable be- 

 tween the trap-crop plats and the check plats. This was true both in 

 the experiments of 1906-7 and of 1907-8, which were conducted on 

 another field. 



The cause of the failure of this method can not be that a sufficiently 

 susceptible host plant was not chosen, for the variety of cowpea used 

 is very susceptible. Furthermore, cowpeas had been gro\^Ti fre- 

 quently on that land, so that the nematodes were, so to say, accus- 

 tomed to that crop. The period of growth allowed was carefully 

 checked by microscopical examinations so as to avoid any chance of 

 letting the development of the nematodes progress too far, for if that 



1 Frank, 1885. 

 217 



