10 



CIRCULAR 516, U. S. DEPT. OF AGRICULTURE 



Table 1. — Results of tests on control of the cyclamen mite on gerbera by immer- 

 sion in hot ivater and by vapor-heat treatment, Washington, D. C, and Babylon, 

 N. Y., 1934 



IMMERSION IN HOT WATER 



Duration of treatment 

 at 110° F. (minutes) 



Tests 



Adults 

 in 

 test 



Mor- 

 tality of 

 adults 



Quiescent 



mites 

 ("pupae") 



in test ! 



Mor- 

 tality of 

 quies- 

 cent 



mites 



Larvae 

 in 



test 



Mor- 

 tality of 

 larvae 



Eggs 



in 

 test 1 



Mor- 

 tality of 

 eggs 



5 



Num- 

 ber 

 1 

 1 

 1 

 2 

 1 



Num- 

 ber 

 42 

 59 

 135 

 169 

 134 



Percent 





 2 93.2 

 100.0 

 100.0 

 100.0 



Number 

 3 



Percent 

 



Num- 

 ber 

 28 

 9 

 37 

 96 

 25 



Percent 

 

 100.0 

 100.0 

 100.0 

 100.0 



Num- 

 ber 



Percent 



10 







15 



38 

 60 

 31 



100.0 

 100.0 

 100.0 



328 



520 

 67 



100.0 

 100 



20 ... 



30 



100 







EXPOSURE TO VAPOR HEAT 



5 



10 



15 



20 



30 



40 



60 



Untreated checks. 



49 

 76 

 122 

 110 

 198 

 204 

 108 

 258 





 2 88.1 

 2 77.8 

 2 98.2 

 100.0 

 100.0 

 100.0 







100.0 

 100.0 

 100.0 

 100.0 

 



17 

 21 

 37 

 31 

 62 

 62 

 62 

 112 





 90.5 

 81.0 

 100.0 

 100.0 

 100.0 

 100.0 

 



196 

 357 

 226 

 219 



427 



100.0 

 100.0 

 100. 

 100.0 

 



1 The presence of eggs and "pupae" was ignored in tests where the adults or larvae survived as the surviv- 

 ing adults might have laid the eggs, and surviving larvae may "have pupated after the treatment. 



2 Survivors were in pubescence of young leaves and in folds of others. 



PLANT TOLERANCE 

 TOLERANCE OF GERBERAS TO HEAT TREATMENTS FOR MITE CONTROL 



In preliminary tests seedling gerberas in 3- to 6-inch pots were 

 immersed in water at 110° F. for 10, 15, 20, 25, and 30 minutes. No 

 injury was evident on plants immersed from 10 to 20 minutes, but the 

 injury ranged from none to severe on the foliage of plants immersed 

 from 25 to 30 minutes. In the case of partially grown leaves (fig. 6), 

 injury consisted in the collapse and browning of the marginal tissue 

 along the midvein near the base, whereas younger and older leaves 

 w T ere uninjured. Considerable individual variation in the degree of 

 injury occurred among these seedlings that were given similar treat- 

 ments. This individual variation was shown to hold true for the 

 five named varieties of gerbera that were made available for experi- 

 mental use (table 2), but all were uninjured by a 20-minute immer- 

 sion. Of these varieties the Ruby was the most tender since it was 

 slightly injured by a 25-minute immersion and severely injured or 

 killed by a 30- to 40-minute treatment. The more resistant varieties, 

 Double Pink, Orange Perfection, and Vesuvius, were slightly injured 

 by a 40-minute immersion. From observation on the tolerance of sev- 

 eral hundred seedlings and these varieties to heat treatments in a 

 commercial greenhouse, it would appear that the variety Ruby repre- 

 sents the most tender type and Vesuvius the most tolerant. 



