BEGONIA LEAF-BLIGHT NEMATODE 7 



nematode. A temperature of 116.6'^ F. for 5 minutes reported by Gill deviates 

 but slightly from these results. It is noteworthy that the minimum water tem- 

 perature lethal to the begonia leaf-blight nematode has been found to be con- 

 sistent by those who have considered the problem. The wider deviations from these 

 lethal temperatures, noted earlier, suggest the existence of differently acclimated 

 strains or even distinct species. Inaccuracies and variations in technique may 

 also be factors accounting for slight discrepancies in the results. 



\\Z 113 IK \15 116 117 118. II? 120 121 \^^ 125 (24 



TtnPERATUT^E ® FflHT^EMHZIT 



Figure 3. Time required to kill the begonia leaf-blight nematode at di.ferent water tem- 

 peratures. 



Tolerance of Plants 



In all of the experiments, infested leaves were always injured, more intensely 

 browned, ultimately killed by the water bath, and finally had to be removed 

 from the plants. This was true even though the symptoms of the disease were 

 only slightly evident. The removal of these leaves was necessary to preserve 

 the healthy appearance of the foliage. Such being the case, the practice of 

 pinching off and destroying infested leaves before the hot-water treatment seems 

 preferable and this sanitary practice would be a valuable supplement to the 

 hot-water treatment in the direction of better control. In general, a range of 

 temperature of 123°-120° F. for 1 minute, 118°-115° F. for 3 minutes, and 115"- 

 113° F. for 5 minutes was safe. Some slightly higher tolerant temperatures at 

 these intervals were noted. In addition, frequently the 5-minute treatment 

 appeared to cause some hardening of the foliage (Table 1). At all the temperatures 

 within the 5-minute period of submersion which were lethal to the nematode, 

 except a few of the more extreme treatments, i.e., 124-123° F. for 1 minute, 123- 

 120° F. and 126-123° F. for 3 minutes, and 120-118° F. for 5 minutes, the younger 

 leaves and shoots and the buds were not injured and new growth followed the 

 treatment. Some of the treatments which gave excellent control of the disease 

 without injury are illustrated in Figure 4. 



