CONDITIONS FAVORING ROOT-KNOT. 43 



exposed to o;reat cold. The writer saw root-knot abundant on gin- 

 seng in a slat shed in Menominee, Mich., where the soil a year or so 

 before froze to a depth of more than 3 feet and where outside the 

 shed water pipes 6 feet beneath the surface were frozen, so the writer 

 was informed. In spite of this cold the nematode injuries were bad 

 the next year. In York, Nebr., where the temperature goes below 

 zero every year and sometimes reaches nearly or quite to —30° F., 

 this nematode survived the winter in peony roots which remained 

 out of doors without protection. In New York State ginseng and 

 alfalfa are both more or less affected with root-knot, while in West 

 Virginia, along the Ohio River, clover is badly affected. It thus 

 becomes apparent that cold alone does not destroy the pest in the 

 soil. To be sure, Bailey ^ placed soil containing root-knot nematodes 

 in boxes and set some of the boxes out of doors through the winter. 

 In the spring the boxes kept indoors still had living nematodes, as 

 shown by gall formations upon plants grown from seeds sown there, 

 while the boxes left out of doors were free from nematodes. It seems 

 probable that the soil in this case dried out in the freezing process 

 sufficiently to kill the nematodes. Ortlinarily, however, the frozen 

 soil remains in connection with soil moisture below, and so the drying 

 out and consequent destruction of nematodes does not occur. 



The root-knot nematode does not become active in the soil and 

 begin to penetrate the roots of susceptible plants until the soil begins 

 to be warm. In the tropical and subtropical regions plants are sub- 

 ject to attack the year around, but the farther north one passes the 

 longer is the winter period of comparative immunity from injury by 

 this pest. Tlius, in Miami, Fla., there is no dormant period for the 

 nematode. In northern Florida, however, crops planted in the latter 

 part of November or in December show comparatively little injury, 

 nor does the injury begin to be severe until the middle of February or 

 early in March. On the other hand, plants sown in October are in- 

 fected before the soil becomes cool and are badly injured, the nema- 

 todes continuing to develop and spread within the tissues when it is too 

 cool for them to spread outside through the soil. AtMonetta, S. C, 

 about half way between Columbia and Augusta, Ga., in the writer's 

 experiments no infection by nematodes could be obtained before the 

 middle of April, while it was the middle of May before they became 

 really active. By the end of September or the middle of October 

 their activity had begun to decline. 



Frank - assumed that the chief period of infection was in the spring. 

 He was in error in this statement, for the writer's experiments show 

 that the nematodes are more active in midsummer and that infec- 



• Bailey, 1892, pp. 157-158. » Frank, 1885. 



217 



