BEGONIA LEAF-BLIGHT NEMATODE 11 



All diseased leaves should be removed and destroyed before the hot-water 

 bath. Diseased leaves which escape removal are injured by the treatment even 

 though but slightly infested. 



Accurate thermometers in one- or two-degree graduations, accuracy in opera- 

 tion, and agitation of the bath water during the treatment are important. 



Although there is no particular evidence to show the value of shading in this 

 work with begonias, it is, according to Smith (11), desirable to give this protec- 

 tion to certain florists' crops for 24 to 48 hours after a 15-minute treatment at 

 119° F. as a precaution against injury. Staniland and Beaumont (12, 13), working 

 with strawberry and violet runners, advise, instead, plunging the stock in cold 

 water immediately after the hot-water bath. 



In view of the foregoing considerations, treatment for one minute at 121-120° F., 

 two minutes at 119-117° F., or three minutes at 118-115° F. is recommended 

 when the disease exists in the stock. The highest water temperature should 

 prevail at the beginning'of the submersion period and the maximum temperature 

 should be restored for each new lot of plants. In view of the varying conditions 

 under which the plants are grown in different establishments and the fact that 

 such conditions can influence susceptibilit\- to injury, it is strongly recommended 

 that the grower first treat a small number of potted plants of each susceptible 

 variety before undertaking treatment of the entire lot. 



The same temperature-interval water baths are recommended for healthy 

 leaves selected for propagating from stock where the disease exists. The leaves 

 should be placed in a closed wire basket or carefully wrapped in cheesecloth 

 and completely submerged during the interval of treatment. 



SUMMARY 



The culture of Lady Mac, Melior, and Marjorie Gibbs begonias represents 

 a large enterprise in many floricultural establishments in Massachusetts. The 

 leaf-infesting nematode, Aphelenchoides fragariae (Ritzema-Bos 1891) Christie 

 1932, commonly known as Aphelenchus olesistus Ritzema-Bos, is often a serious 

 menace to the successful culture of these begonias. 



Sanitary and cultural methods within the limits of good plant growth and 

 commercial practice are not effective in arresting the progress of the disease. 

 Propagating from stock free of the leaf-blight nematode disease is the best measure 

 of control, other desirable sanitary- and cultural practices being followed. 



All stages of the nematode in the leaves are killed by submerging potted in- 

 fested plants in water of a mean temperature of 115° F. for 5 minutes, 117° F. 

 for 3 minutes, 118^° F. for 2 minutes and 120}^° F. for 1 minute. In general, 

 temperatures of 123°-120° F. for 1 minute, 118°-115° for 3 minutes and 115°-113° 

 F. for 5 minutes were safe except to infested leaves, which were severely injured. 

 In a few instances a trace or a very small number of nematodes revived after 

 the treatments but either no further symptoms of disease appeared or the amount 

 of disease after 3 months was negligible. Untreated stock continued to show- 

 infested leaves and ultimately the contrast between treated and untreated plants 

 was striking. 



Submersion of plants in water at temperatures of 121°- 120° F. for 1 mmute, 

 119°-117° F. for 2 minutes, or 118°-115° F. for 3 minutes is recommended for 

 infested stock. The treatments should be tried on a few plants before they are 

 applied on a large scale. 



The submersion of begonia plants in hot water as an eradicative control meas- 

 ure should be done at least three months before the marketing season to permit 

 the development of well-foliaged plants during the ensuing interval. The treat- 



