370 Diseases of Greenhouse Crops 



check is in burning nicotine papers at the rate of 2 

 sheets to every 1,000 cubic feet of greenhouse space. 

 Fumigation is best performed at night in a moist 

 atmosphere. Early in the morning the treated house 

 is opened and thoroughly aired. Fumigation with 

 nicotine liquid extracts is also effective in controlling 

 thrips. Russell * recommends the use of one ounce 

 of liquid nicotine (containing 40 per cent, nicotine) 

 to every 1,000 cubic feet of greenhouse space, or 

 from one and a half to two ounces of the weaker 

 strengths. The liquid is evaporated over small 

 lamps or stoves, and to prevent scorching is diluted 

 with water. Greenhouse thrips may also be kept in 

 check by fumigation with hydrocyanic-acid gas. 

 For directions, see p. 385. 



Mealy Bugs {Pseudococcus sp.J^ 



Mealy bugs are really scales without armor. They 

 are sprinkled over with a white mealy wax or pow- 

 der which gives them the name. In the greenhouse 

 there seems to be but two species of importance, 

 namely, Pseudococcus citri and P. longispinus. 



Control. The easiest way to keep this pest in 

 check is to liberally syringe the plants with water 

 at a fair pressure. This will wash the insects off the 

 plants and permanently dislodge them. Spraying 

 with a mixture of one paft nicotine sulphate to 750 

 parts of water will also keep them in check. Fumi- 



* Russell, H. M., U. S. Dept. of Agr., Bureau Entomology Cifd 

 151:1-9,1912. 



