THE MONTHLY BULLETIN. 61 



The worms are distrihiitetl from one section to another by infeeted 

 seed potatoes, transplanted seedlings, nursery stock and the like. Irri- 

 gation is, one of the most important methods of carrying the worm from 

 one Held to another, and one of the most difficult to control. Farming 

 imi)lements may transfer Avorms by means of the adhering soil, but 

 our experiments show that if the soil is thoroughly dried out all the 

 worms are killed so there is probably very little danger from the drift- 

 ing of soil by the wind. Some experiments were carried on to test 

 the possibility of spreading the parasite by means of the manure of 

 animals fed upon infested plants, and it was found that all eggs and 

 larvas were destroyed in the stomach by the gastric juice. 



The eggs and larvas are quite resistant to frost, but freezing tempera- 

 tures for a sufficient length of time will kill them. The long cold 

 winters of the northern and eastern states are probably the chief cause 

 for the absence of any eelworm problem outside of the greenhouses. 

 The character and consistency of the soil plays some part in the degree 

 of resistance to frost. We are now at work to determine the depth to 

 which the worms may penetrate different soils. 



It has been suggested that fields might be rid of the worms by flooding 

 them with water but our experiments indicate that at least three months 

 submersion would be necessary to make this method effective. 



On the other hand we have found a surprising lack of resistance to 

 drying. Eggs and larvse placed on a glass slide and allowed to dry out 

 for a few minutes fail to show any signs of further development, and if 

 infected roots and tubers are allowed to thoroughly dry out all the 

 contained eggs and larva? are killed. 



There is also very little resistance to heat. Some eggs and larvae 

 were placed in an incubator at a temperature of 40° C. with the idea 

 of hastening their development. While development was greatly 

 accelerated in the first few hours, to the extent that some of the eggs 

 began hatching before the embryos had reached the proper stage of 

 development, at the end of 18 hours every egg and larvee was dead. 

 Infested potato tubers were likewise placed in the incubator at various 

 temperatures for different periods of time, and it was found that 

 23 hours was sufficient to destroy the parasites without apparently 

 interfering with the germinating power of the potato. A longer period 

 of exposure than this impaired or destroyed the germinating power. 

 Since it is difficult to be sure of one's seed if it comes from an eelworm 

 locality, because a slight infestation may easily escape even careful 

 inspection, it is possible that such seed may be made innocuous by 

 placing it in an oven for 24 hours at a temperature of 40° C. before 

 planting. We are now testing this out. 



A question frequently ssked by the farmer is, '^ Can't we treat the 

 seed and soil with some chemical substance which will rid them of the 

 worms?" Previous investigators have found that liberal treatment of 

 the soil with alkaline fertilizers seems to be unfavorable to the worms 

 but cannot be counted upon to exterminate them. One Nevada rancher 

 claimed that he liad a method of applying bluestone which kept the 

 eelworms from bothering him. We treated worms and infested plants 

 with various strengths of copper sulphate solution and found that even 

 a one per cent solution, which is distinctly poisonous to vegetation, act- 

 ing for two days directly on the worm, failed to destroy a single egg. 



