CONTROL OF CYCLAMEN AND BROAD MITES ON GERBERA 7 



Thermocouple readings made in crowded parts of the crated plants 

 during their immersion showed that the temperature increased very 

 unevenly during the 15-minute treatment. In one of three series 

 where the plants were very closely packed in the box, the temperature 

 among the crowns was 106° at the end of 5 minutes. 108° in 10 min- 

 utes, and 109° at the end of 15 minutes. In two other series a tem- 

 perature of 110° was attained in 5 to 6 minutes. Figure 5 shows 

 the temperatures as averaged for the three series to have been 108.3° at 

 the end of 5 minutes and 109.5° at the end of 10 and 15 minutes of 

 immersion. These records reveal the fact that the water temperature 

 among closely packed plants increases irregularly to the point lethal 



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O— READINGS AMONG LEAVES IN BOX 

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2 3 4 5 6 7 8 9 10 II 12 13 14 15 . I 2 3 4 5 6 7 8 9 10 II 12 13 14 15 16 17 18 1920, 

 TIME DURING TREATMENT(MINUTES) TIME SUBSEQUENT TO TREATM ENT (MIN UTES) 



Figure 5. — Temperature changes occurring among gerbera plants during immer- 

 sion in water at 111° F. and also during period following removal from the 

 bath when packed in masses in crates (a and ft) or in thin layers in a screen 

 tray (c). 



to the mites and seem to account for the fact that all mites were not 

 being killed. Headings (fig. 5) taken after the plants were removed 

 from the bath showed that in certain cases the temperature decreased 

 very slowly among the leaves, and this probably accounted for an 

 increased amount of plant injury (fig. 6). 



The preferred treatments would permit rapid and even penetration 

 of hot water to all parts of the plant occupied by the mites during 

 treatment, then rapid cooling subsequent to treatment, to reduce plant 

 injury. To meet these requirements a pipe-frame tray was made, 

 covered with wire of %-inch mesh and equipped with hinged lid, 

 pulleys, and rope, so that it could be lowered into and raised from an 

 800-gallon vat of water (fig. 7). As many as 600 plants can be 



