14 CIRCULAR 516, U. S. DEPT. OF AGRICULTURE 



SUMMARY AND CONCLUSIONS 



Investigations have been made on the habits of the cyclamen mite, 

 the broad, mite, and several species of saprozoic tarsonemid mites 

 occurring on gerbera plants in greenhouses. 



The broad mite builds up infestations to large numbers and by 

 feeding on the foliage causes severe dwarfing and curling of the leaves, 

 resembling injury caused by a disease. Flowers are attacked and the 

 rays are aborted and decolorized. 



The cyclamen mite feeds on the foliage and produces bronzed 

 patches along the midribs and slight curling of foliage. The flowers 

 are attacked in the bud stage and the rays are deformed, the flowers 

 being thus rendered unsalable. Although the cyclamen mite causes 

 less conspicuous injury than the broad mite, it is responsible for greater 

 crop losses to gerbera growers. 



Among the various treatments that are effective against the broad 

 mite, dusting the plants with sulphur appears to be the most effective. 



The cyclamen mite has not been controlled by the various sprays, 

 dusts, and fumigants applied against it on gerbera. Heat treatments, 

 either with hot water or with vapor heat, have been found effective. 

 Divided plants immersed for 15 to 20 minutes in water at 110° F., 

 or treated 30 to 60 minutes in vapor heat at the same temperature, were 

 freed of mites. Failure to secure control by the hot-water treatment 

 as employed by some growers was found to be due to lack of uniform 

 penetration of heat when the plants were treated in densely packed 

 crates. This difficulty was overcome by treating the plants in a large 

 tray on which they were placed in a thin layer. 



Considerable differences in tolerance to heat treatments are ap- 

 parent among varieties of gerbera. In a hot- water treatment at 

 110° F., the most tender varieties are injured by a 25 -minute immersion, 

 while others withstand a 40-minute immersion. In vapor-heat treat- 

 ments at 110°, the tender varieties are slightly injured by a 60-minute 

 exposure, while the resistant ones may be treated 120 minutes with 

 only slight injury. 



In tests to determine whether gerberas would withstand heat treat- 

 ments for control of the root-knot nematode, the plants were killed 

 or severely injured by 30-minute immersion in water at 116° and 120° 

 F. Chemical dips were generally injurious to the plants when applied 

 in conjunction with treatment for the cyclamen mite. 



In practical control operations 60,000 plants were successfully 

 treated in hot water for mite control. Precautions were taken to 

 prevent this material from being reinfected, and no mites or mite 

 injuries were found among these plants during the two successive 



