368 Diseases of Greenhouse Crops 



Maryland, Beaute Poitevine, Mme. Laudry are all 

 susceptible to the attacks of the mites. On the other 

 hand, the variety Le Favorite seems to be immune. 

 It is not known whether or not there are resistant 

 varieties of cyclamen, chrysanthemum, or snapdra- 

 gon. Because of the extremely primitive respiratory 

 system of mites, it is difficult to keep them in check 

 by fumigation with various gases. It is safer there- 

 fore to resort to spraying. However, when a plant 

 becomes badly infested, no attempt should be made 

 to save it. It will be cheaper to destroy it by fire. 

 Dusting with tobacco or sulphur will do little good. 

 Moznette * obtained good results by dipping the 

 plants in an oil emulsion called Yel-ros mixed in 

 the ratio of one part of Yel-ros to forty parts of 

 water. Yel-ros contains a good deal of Xylol which 

 is penetrating. This treatment, however, is recom- 

 mended for older plants. Young plants may be 

 greatly injured by burning. "Black leaf 40" and 

 water in the ratio of 1 to i,ooo, or of one teaspoon- 

 ful to a gallon of water will effectively control the 

 mite. By adding three to four pounds of ordinary 

 soap to each 100 gallons of the above solution, it 

 will be made to adhere better to the treated plants. 

 Spraying should begin before the mites attack the 

 plants and should be continued every ten days until 

 the flower buds are ready to open. At this stage the 

 spraying should cease as otherwise the petals may be 

 discolored. 



* Moznette, G. F., U. S. Dept. of Agr.. Jour. Agr. Research 

 10:373-390, 1917. 



