294 MASS. EXPERIMENT STATION BULLETIN 246 



cent has been found safe for use on cucumbers which have been sprayed with 

 white mineral oil emulsion. This dust contains other active ingredients, which 

 bring the cost up to about 10 cents a pound. A home-made dust of much 

 greater effectiveness and similar safety can be prepared by thoroughly mix- 

 ing 15 pounds of dusting sulfur with 85 pounds of either 200 mesh gypsum 

 or talc at a cost of about 1^ cents per pound for materials. The latter dust 

 is preferable, but since a commercial sulfur dust of this composition is not 

 obtainable, its preparation at home is recommended. 



Summary of Recommendations. 



Learn to recognize the greenhouse red spider, the cucumber powdery mil- 

 dew, and the injury which they inflict. 



Prevent the establishment and spread of these pests by practicing repressive 

 measures. 



For red spider, spray witli a highly refined white mineral oil enuilsion 

 whicli is free from injurious carbolic or cresylic compounds. 



For powdery mildew, practice proper methods of ventilation, watering, and 

 heating, and use small amounts of high grade dusting sulfur. In dull, cool 

 weather or if powdery mildew is troublesome on lower sides of leaves, spray 

 with copper fungicides or potassium sulfide. 



When both pests are present, spray with a highly refined white nuneral oil 

 emulsion and dust with a low "free sulfur content" dust in bright, warm 

 weather. In dull, cool, weather, or if powdery mildew is troublesome on lower 

 sides of leaves, spray M'ith a copper fungicide combined with highly refined 

 white mineral oil emulsi-jn. 



Precautions When Using Insecticides and Fungicides. 



Do not funugate with hydrocyanic acid gas as long as tliere is residue from 

 cojjper fungicides on the leaves. 



Do not spray with highly refined white mineral oil emulsion while there is 

 residue from high "free sulfur content" dusts on the leaves. 



Publication of this document is approved by the 

 Commission on Administration and Finance 

 5 M-ll-'28. No. 3932. 



