CONTROL OF ROOT-KNOT. 59 



been mentioned, reference being made to the conditions in the Ever- 

 glade islands, where the never submerged tops of the islands are full 

 of root-knot and the annually submerged sides are free from it. The 

 writer has records of fields in Georgia badly infested with the root- 

 knot nematode that were free from the trouble after a spring freshet 

 that kept the ground submerged several days. 



Apparently flooding, unless possibly of long duration, will not kill 

 the nematodes inclosed within the root galls, so that if such knotted 

 roots of perennial plants are present the flooding must be continued 

 much longer. In Yuma, Ariz., under the writer's directions a field was 

 flooded. It had once been a vineyard of Old World grapes, but these 

 had become improfitable owing to the ravages of the root-knot, and 

 the vines had been cut down or pulled up. Many of the roots, however, 

 were left in the ground. The next year the field was planted to melons. 

 When the writer saw tlie field in May, 1907, the young cucumber 

 and melon plants were dying from root-knot and the pest was found 

 in the old living grape roots. The field was flooded the following 

 winter, but root-knot was again prevalent tlie following spring, 

 although apparently not so abundant. It seems likely that the vine 

 roots may have harbored and saved from destruction many nema- 

 todes, or perhaps the flooding was not continued long enough. That 

 under some circumstances even three weeks is insufficient appears to 

 be the conclusion to be drawn from an experiment performed at the 

 writer's suggestion by a fruit grower and nurseryman in California. 

 He kept submerged for three weeks his field of sandy alluvial soil 

 which was badly infested by nematodes. Afterwards grape cuttings 

 and peach seedlings were set out in it. The grapes (a resistant sort, 

 Rupestris St. George) showed no root-knot, but the peaches became 

 knotted. This period seems excessive in view of laborator}^ results, 

 and is not entirely free from doubt as to other possible means of in- 

 fection, yet, until disproved, three weeks should be regarded as not 

 enough time to exterminate the nematode by flooding. 



It is of interest that flooding the soil is claimed by Stif t ^ to be of no 

 value against the closely related sugar-beet nematode. 



Flooding, then, can not be recommended as a certain means of ex- 

 terminating root-knot under all circumstances. Probably the soil 

 should be flooded at least 25 days; in the laboratory the nematode 

 larvae usually succumbed much sooner when isolated and placed in 

 water. Furthermore, no roots of perennial susceptible plants must be 

 present. When water is expensive or means of flooding are not at 

 hand, or when the soil is too porous, it will be out of the question to 

 try this method. The subject is one, however, that needs further 

 investigation. It wiU be of interest to call attention to the phenom- 



1 Stift, 1903. 

 217 



