6 MASS. EXPERIMENT STATION BULLETIN 348 



from begonia; 115° F. for 12 minutes was lethal to the nematode from chrysan- 

 themum and 94 percent were killed in 10 minutes at this temperature; 115° F. 

 for 10 minutes and 120° F. for 5 minutes was lethal to the nematode from Cape 

 Cod, Massachusetts, strawberry plants and at 118° F. for 5 minutes 96 percent 

 were killed; and 120° F. for 15 minutes was lethal to the nematode from North 

 Carolina strawberry plants. These conditions were minimum for a completely 

 lethal effect on eelworms in 0.5 cc of water in test tubes. None of the investigators 

 considered treatments of less than five minutes. This appears to be important 

 in commercial practice both from the viewpoint of practical utility and the 

 probability of greater plant tolerance against injury. 



EXPERIMENTAL PROCEDURE AND RESULTS 



In experiments here reported, entire plants in 5-inch clay pots and pans were 

 completely submerged in water in a tub. The water was first brought to the 

 desired temperature with hot water piped from the water heating system and in 

 the interval of submersion the water was constantly agitated. The temperature 

 at the finish of the submersion period was recorded and the mean of the start 

 and finish temperatures was used in plotting the graph of the results. There 

 is no need for constant water temperature. It would complicate rather than 

 simplify the hot-water treatment in commercial practice. The body of water 

 in the experiments was large enough to keep the temperature during the interval 

 of treatment within a few degrees of the starting temperature. 



The effect of the hot-water treatment on the nematode was determined by 

 examining bits of epidermis from the lower surface of infested leaves. The 

 first examinations were made a few daj's after treatment of the plants. Other 

 examinations were made at later intervals, and final observations in most cases 

 were made more than two months after the treatment. The interval was ample 

 to reveal instances of recovery and the hatching of eggs. Nematodes which sur- 

 vived the treatment were active and turgid. Those showing no motion and 

 wholly or partly collapsed were regarded as being dead. Records were also made 

 of any injuries to the foliage, the shoots and the plants as a whole during the course 

 of observations. 



Leaves of the varieties Lady Mac and Marjorie Gibbs were treated with hot 

 water to determine the tolerance and effect on rooting, and hence the practi- 

 cability of the treatment for leaves gathered for propagation where infestations 

 exist in the mother plants. Both infested and healthy leaves were used in the 

 tests. The leaves were wrapped in cheesecloth and kept submerged in the water 

 bath throughout the interval of treatment. They were then inserted in sand for 

 rooting. 



SUBMERSION OF POTTED PLANTS IN HOT WATER 



Water Temperatures Lethal to Nematode 



The kill of the nematode, both eggs and worms, followed the interval tem- 

 perature curve shown in Figure 3 corresponding to mean temperatures of 115° F. 

 for 5 minutes, 117° F. for 3 minutes, 118J^° F. for 2 minutes, and 120)^° F. for 

 1 minute. No difificulty was experienced in eradicating the organism without 

 causing injury to the plants. The lethal effect of temperature on the nematode 

 appeared to be more constant than the tolerance of the leaves to the treatment, 

 which seemed to indicate a variation in tolerance of individual plants. Christie 

 and Crossman reported a temperature of 115° F. for 5 minutes lethal to the 



