CONTROL OF ROOT-KNOT. 65 



NONSUSCEPTIBLE CROPS. 



The most promising method, and the one that has given the best 

 results wherever carefully tried, is that of growing crops that are not 

 subject to root-knot until the nematodes causing the disease are starved 

 out. To carry out this method successfully several things are requi- 

 site: (1) The crops planted must be free from nematode attack, so 

 that the larvae in the soil may not be able to fmd any nourishment 

 to sustain their life and enable them to undergo their development. 

 (2) The crop grown should at least pay the expense of working the 

 land, as well as the rent, taxes, etc. (3) At the same time, if possible, 

 the crops should enrich the land, or at least not impoverish it. (4) 

 The plants must make such a vigorous, dense growth as to choke out 

 all weeds or other plants that might harbor nematodes and permit 

 them to develop and produce their numerous eggs. 



On referring to the list of susceptible plants it will be seen that with 

 few exceptions none of the ordinary farm crops fulfill the first require- 

 ment. However, the following plants appear to be free from nematode 

 attack, at least under most conditions: Cowpea (the Iron variety), all 

 species tested of Stizolobium (the velvet bean and close relatives), 

 Florida beggarweed (Meihomia mollis), peanut {Arachis liypogaea), 

 rye (Secale cereale), most varieties of winter oats {Avena sativa), crab- 

 grass (Syntherisma sanguinalis) , and possibly a few others. Webber 

 and Orton ^ first called attention to the nematode-resistant quality of 

 the Iron cowpea and recommended its use in combating root-knot. 

 The velvet bean and beggarweed have been recommended by Rolfs,^ 

 of the Florida Agricultural Experiment Station, who has also pointed 

 out the value of crab-grass in a plan of rotation for reducing the num- 

 ber of nematodes. Thus, he found the nematodes far less abundant 

 the next 3^ear after an infested field was allowed to grow up to crab- 

 grass for one year. 



The following rotations were planned by the waiter for his work at 

 Monetta, S. C, there being four plats measuring, respectively, 0.152, 

 0.217, 0.217, and 0.166 acre: 



Table III. — Rotation of crops planned for four experimental plats at Monetta, S. C. 



This experiment was planned for three years. It was begun in the 

 fall of 1905. It was planned to keep careful records of all yields, etc., 

 but in some cases the records are lacking. Unfortimately, the soil 



' Webber and Orton, 1902. * KoUs, 1S98. 



217 



