414 STATE BOARD OF AGRICULTURE. 



EXPERIMENTS ON THE CONTROL OF TUE ROOT-KNOT 



NEMATODE.* 



Technical Bulletin No. 20. 

 BY J. A. MC CLINTOCK_, 



Agent B. P. I. in charge of Ginseng disease Investigation of Michigan. 



The root-knot nematode, Heterodera radicicola, (Greet) Mtiller, has 

 proven to be a serious pest of many crops in the southern states, and in 

 some of the western states it has caused considerable trouble on potatoes 

 and sugar beets. In many of the northern states, this nematode has 

 caused serious trouble on greenhouse crops and on such intensive garden 

 crops as ginseng. 



The life history of this parasite has been worked upon by (1) Atkin- 

 sonf, (6) Stone & Smith, (2) Bessey, (3 and 4) Cobb, and control meas- 

 ures have been worked out for greenhouse conditions by Stone & Smith; 

 while Bessey and (5) Rolfs have recommended rotations that tend to keep 

 the root-knot nematode more or less under control in certain field 

 crops. Much still remained to be worked out in the way of control 

 measures for intensive crops like truck crops, ginseng, golden seal, etc. 



For an account of the complete life history of the root-knot nematode 

 see Bessey (2). Briefly it is as follows: 



In about twenty-five days after the female enters a root, she has 

 reached sexual maturity and begun to lay eggs. These eggs which are 

 85-98 microns in length by 34-40 microns in thickness, are surrounded, 

 as laid, by a gelatinous substance which holds them together in a mass. 

 In the case of firm, woody tissues, the eggs seldom reach the surface of 

 the knot, but j)roduce numerous larvfe which make their way to the sur- 

 face and enter new roots. Where the root-knot is in softer tissues, as 

 those of various herbaceous plants, the eggs are often forced through the 

 tissues and cling in small masses to the surface of the knot. The num- 

 ber of eggs laid by a single female varies somewhat, but counts seem to 

 shoAv that it is between four and five hundred. In all cases where the 

 number of eggs used in experiments is recorded, it is on the basis of four 

 hundred eggs per egg mass, so in most cases the number of eggs treated 

 probably ran over rather than under the number recorded. Under favor- 

 able conditions, the eggs probably begin to hatch within a few days 

 after being laid, thus making the complete life cycle about thirty days 

 under favorable conditions. 



*The work upon which this paper is based was carried on under a cooperative apreenient between 

 the Bureau of Plant Industry and the Michigan Experiment Station, and in somewhat different form 

 was accepted as a thesis for the degree of Master of Science in the Department of Plant Pathology, 

 University of Wisconsin. 



tThe number with the author's name refers to the number of the article referred to as 

 listed in the bibliography at the close of this paper. 



