366 Diseases of Greenhouse Crops 



stroys their web and drives them off since red spiders 

 cannot thrive under moist conditions. Plants with 

 hardy foliage may successfully be rid of the spider 

 by spraying with a solution composed of one-half 

 pint of "Nicofume" liquid, and two quarts of con- 

 centrated lime sulphur in 25 gallons of water. One- 

 half ounce of salt dissolved in one gallon of water 

 seems to control red spider on carnations. This, 

 however, may bum the foliage of most other plants. 

 Investigations by Vinal * seem to show that no 

 fumigant was efficient in killing red spiders without 

 severely hurting cucumber plants. Sulphur burned 

 to form sulphur dioxide proved very effective in 

 killing all stages of mites. However, since this 

 gas is very deadly to plant life, it can only be used 

 as a fumigant to free empty houses from spider in- 

 festation. For the control of all stages above the 

 egg stage, graying with lemon oil or linseed oil 

 emulsion proved very effective. Lemon oil may be 

 used at the rate of 1 part in 20 parts of water, and 

 applied thoroughly. For directions to prepare lin- 

 seed oil emulsion, see p. 399. 



Mites {Tarsonetnus pallidus Banks) 



Mites (fig. 78, a and b) are really closely related 

 to red spiders. The species Tarsonetnus pallidus is 

 of particular interest to greenhouse growers because 

 it attacks cyclamens, snapdragons, geraniums, and 

 chrysanthemums. 



'Vinal, S. C, Mass. (Amherst) Agr. Ezpt. Sta., Bui. 179: 153- 

 182, 1917. 



