CONTROL OF CYCLAMEN AND BROAD MITES ON GERBERA \ \ 



Table 2. — Varietal difference among gerbera plants in their tolerance to heat 

 treatments, Washington, D. C, and Babylon, N. Y., 1934 



IMMERSION IN HOT WATER 



Duration of 



Degree of injury to- 



treatment at 

 110° F. (minutes) 



Ruby 



Double 

 Pink 



Orange 

 Perfection 



Incompa- 

 rable 



Vesuvius 



Seedling varieties 



15 



None 



_..do 



Slight 



Severe 



...do 



None 



...do 



_..do 



...do 



Slight 



None 





None 



-_.do 



...do 



...do 



Slight 





20 



25 



...do 



...do 



__.do 



Slight 



None 



-_.do 



Slight 



Do. 



30 ..-• 





40 















EXPOSURE TO VAPOR HEAT 



30 



45 



60 



None 



—do 



Slight 



Severe 



None 



...do 



Slight 



—do 



None 



...do 



--do 



—do 



Slight. 







None 



...do 



...do 



—do 



Slight 





90 . . 





120 

















Tolerance of seedlings and varieties of gerbera plants to vapor- 

 heat treatments at 110° F. indicated (table 2) that a 60-minute treat- 

 ment causes slight injury to the most tender variety (Ruby) and that 

 a 90-minute treatment caused severe injury or death to plants of that 

 variety, whereas a 2-hour treatment causes slight injury to the two most 

 resistant varieties (Vesuvius and Orange Perfection). 



TOLERANCE OF GERBERAS TO TREATMENTS FOR CONTROL OF NEMATODES AND 



CERTAIN DISEASES 



In cooperation with Freeman Weiss, of the Bureau of Plant In- 

 dustry, United States Department of Agriculture, tests were made to 

 determine the tolerance of gerberas to heat treatments alone for con- 

 trol of the root-knot nematode (Heteroderamarioni (Cornu) Goodey), 

 and also to heat treatments combined with chemical antiseptics to 

 prevent dissemination of certain diseases that kill the plants at the 

 crown. Dr. Weiss has generously made the results of these tests 

 available for inclusion in the present paper. 



In the treatments for control of nematodes one series of tests was 

 conducted in December 1933, in which Vesuvius gerberas survived a 

 30-minute immersion in water at 118° F. but developed weak new 

 growth. Injury was not increased on plants that were immersed im- 

 mediately after the hot-water treatment for 10 minutes in mercuric 

 chloride' (1: 1000) or formalin (1:200), but they barely survived a 

 20-minute immersion in the same chemicals. In another series of 

 treatments conducted on the same variety in May 1934, the plants died 

 in most cases, and the few survivors developed weak new growth after 

 they had been immersed for 30 minutes at temperatures of 116°. 118°, 

 or 120°. 



In other tests with heat treatments for control of mites, antiseptic 

 treatments Avere made in which chemicals were (1) added to the water 

 bath in which the plants were immersed for control of the mites, or (2) 

 added to cold water in which the plants were immersed for 5 minutes 

 immediately after removal from the hot-water bath. Plants of the 



