10 



MASS. EXPERIMENT STATION BULLETIN 348 



to the nematode and the leaf blades were not injured. (Table 2). The hot-water 

 treatment of leaf-cuttings is thus an efificient means of freeing the leaves of any 

 possible but inapparant infestation of the leaf-blight nematode and gives assur- 

 ance of starting the new propagation clean. This treatment should serve as a 

 desirable sanitary practice in preventing the introduction of the organism into 

 the clean sand bench, but it is advocated onl\- when the disease exists in the stock. 



Table 2. — Effect of Hot-Water Treatment of Begonia Leaves 



ON Rooting* 



Temperature Time 

 °F. (Minutes) 



124 

 123-122 



122 

 122-121}^ 

 121-120 

 120-119 



119 



118 

 121-120 

 120-119^ 

 119-1 18 Ji 

 120-119 

 119-118 

 118-117 



Percentage Rooting 



Infested 



Leaves 







25 





 33.3 



25 



Healthy 

 Leaves 



100 



92.8 



100 



85.7 

 100 



92.8 



*Results based on treatment of 12 leaves 



PRACTICAL CONSIDERATIONS AND RECOMMENDATIONS 



The treatment of potted begonias with hot water to be practical must be a 

 rapid operation, especially if a large amount of stock is involved. Submersion 

 of stock in hot water for not more than three minutes, with a short interval after 

 the treatment of each lot of plants to permit the restoration of the maximum 

 temperature of the bath water for the next lot, will enable the grower to do the 

 work in the shortest time. 



The treatment must be safe. Soaking of the soil in the pots would result from 

 a long period of submersion and this would promote decay and damage to the 

 root system. A five-minute treatment, therefore, would be objectionable and is 

 not necessary from the standpoint of control. 



A tank large enough to accommodate a rack of 25 plants seems necessary where 

 a large amount of stock is involved. The volume of water must be sufficient to 

 prevent a temperature drop of more than 3° F. during the period of submersion. 

 As the plants are lifted from the water, they should be tipped to one side to 

 release any water on the soil in the pots. 



As insurance against serious trouble later, the hot-water treatment of begonia 

 stock would seem to be advisable on the first appearance of symptoms of the leaf- 

 blight nematode disease. Submersion of the plants would be more practical in 

 3j/2-inch pots than in 5- or 53^-inch pots and there would be more time for the 

 renewal of shoots and leaves. Treatment after the first of October is not desirable 

 since the subsequent growing period, extending to the Christmas marketing sea- 

 son, is too short to make possible a luxuriant amount of new growth. 



