4 MASS. EXPERIMENT STATION BULLETIN 348 



The submersion of infested plants or root stocks in hot water to eradicate leaf 

 nematodes, mites, and other pests has been advocated in the literature, and the 

 treatment would appear to be a very valuable control measure where it can be 

 done safely. There is considerable literature relative to water temperatures 

 lethal to the leaf-blight nematode, Aphelenchoides fragariae (Ritzema-Bos) 

 Christie, as well as definite recommendations for treating infested plants with 

 hot water as a method of successfully controlling the organism. Aside from the 

 studies of Marcinowski (9) with the begonia variety Gloire de Lorraine in which 

 good control of the nematode without serious injury is claimed, and the studies 

 of Gill (6, 7) with Melior and Lady Mac, reporting no control without decided 

 injury to the plants, nothing has been reported on the cjuestion of tolerance of 

 these begonias to hot-water treatments. The problem, therefore, seemed to justify 

 study. 



LETHAL HOT-WATER TEMPERATURES 



In view of the confusion in the taxonomy of the organism and the interchange- 

 able use of the specific names, olesistus, fragariae, ritzema-hosi and ormerodis, 

 which are associated with diseased conditions in the leaves or crowns of violet, 

 strawberry, fern, chrysanthemum, begonia and many other plants and which 

 some authorities regard as synonymous or merely strains of the same form, 

 a review of pertinent knowledge of temperatures lethal to these nemas on these 

 hosts should be helpful to the understanding of the problem. 



Marcinowski showed that when potted ferns or individual fronds still attached 

 to plants were submerged at 122° F. for five minutes or 131° F. for one minute, 

 the treatment was completely lethal to the nematode. These were the lowest 

 time intervals for these temperatures at which kill was complete. In the first 

 instance the condition of the plants remained good. With Gloire de Lorraine, 

 immersion for five minutes at 122° F. caused the old leaves to shed. The new 

 growth subsecjuently produced strong and healthy shoots. Since the surface of 

 the soil and the pots obviously are populated by the nematode, the immersion 

 of plant and pot was recognized as being essential to the successful control of 

 the pest. Gill found a temperature of 116.6° F. for five minutes lethal to the 

 nematode in begonia leaf tissues and also harmful to the plants. Molz (10) 

 found that in the immersion of bits of infested chrysanthemum leaves for a 

 period of 10 minutes, the lowest completely lethal temperature was 109.4° F., and 

 after immersion for five minutes at this temperature onK- one active nema was 

 observed. At 1 13° F. for five minutes, the kill was complete. Steiner and Christie, 

 according to Dodge (5), controlled the nematode on chrysanthemum by immers- 

 ing roots and crowns in water at 118° F. and 120° F. for 30 minutes, but for 

 growing plants the treatment was not safe. Hodson (8) found that a water 

 temperature of 110° F. for 20 minutes for small stools and 30 minutes for large 

 stools of chrysanthemum was effective. According to Staniland and Beaumont 

 (13), a temperature of 110° F. for 15 minutes was the best treatment for violet 

 runners and over a three-year period caused a marked improvement of the stock. 

 In reports of investigations on control of the strawberry nematode, immersion 

 of stock in hot water is recognized. Brooks (1) recommended a 20-minute sub- 

 mersion in water at 118.4° F.; Christie and Stevens (2) a 30-minute submersion 

 at 118° F.; and Staniland and Beaumont (12) a 15- or 20-minute submersion at 

 110° F., but later found a 30-minute treatment more efficient and preferable if 

 good planting conditions exist. Christie and Grossman (3) showed that a temper- 

 ature of 112°F. for 15 minutes and 115°F. for 5 minutes was lethal to the nematode 



