68 ROOT-KNOT AND ITS CONTBOL. 



From the standpoint of nematode extermination the results were 

 very satisfactory. Both in 1908, after two years of this rotation, 

 and in 1909, after three years, the susceptible plants on part of the 

 plat remained free from root-knot except as specified below. These 

 plants were, as in previous tests, tomatoes, okra, beans, and New 

 Era co\\^eas, all extremely susceptible to root-knot attacks. Sev- 

 eral rows of each were planted in 1908 along the southern edge of 

 the plat, and m 1909 on the part just adjacent to that on the southern 

 part of that portion of the field which had had a rotation of three 

 years. Every plant was carefully dug up and all its roots examined 

 after freemg them from the adhering soil. Every such plant w^as 

 recorded as free, slightly affected, or seriously affected, a separate 

 record being kept of all tlie plants in each hill. 



The field slopes very gradually toward the south from higher, 

 somewhat nematode-infested land on the north. Two slight de- 

 pressions lead somewhat diagonally from the northwest to the south- 

 east. In the spring of 1908 and again in the early summer of 1909 

 Monetta was visited by torrential rains which flooded and very badly 

 washed the fields. Considerable soil from the fields to the north, 

 and especially the badly infested field to the west, was washed down 

 these depressions, settling on them and in the lower (southern) edge 

 of the rotation field. Where these deposits of dirt occurred, and con- 

 fined to these areas, some of the plants showed more or less nematode 

 injury, most near the middle and least along the edges of the depres- 

 sions. Furthermore, a few plants at the edges of the field, i. e., at 

 the east and west ends of the rows, showed nematodes where they 

 were probably introduced from the adjoining land in cultivating, 

 plowing, etc. All the rest of the plants remained nematode free, 

 although this field was badly infested before the experiment began. 



In accordance with suggestions of the writer, IVir. A. D. Jackson, 

 of Denison, Tex., made some rather similar experiments, using Iron 

 cowpeas and rye as his rotation. Certain fields were very badly 

 infested, so badly, indeed, that the crops on them were almost a 

 total failure. By growing the cowpeas two seasons with rye as the 

 winter crop the nematodes were so reduced in number that only 

 20 hills of cantaloupes out of half an acre were affected with root- 

 knot and the crop of melons was excellent. Under date of July 

 10, 1909, Mr. Jackson wrote as follows: 



I am well pleased with the Iron pea. While I have not eradicated the pest entirely 

 by growinti; the poa two .reasons, I have enriched my >soil, have grown a large crop of 

 feed, and the succeeding crop of vegetables has not in any case been materially af- 

 fected (by nematodes]^ 



In Mr. Jackson's fields the writer's and Mr. Jackson's conclusions 

 were that the few nematodes surviving were those that were pro- 



217 



