INSECTS AND DISEASES 41 
existing on the outside surface of the leaf. We 
must attack it, then, from another direction. 
One weapon ready for our use is simply water, 
sprayed over the plant to wash off and drown 
the pests. This is effective against the red 
spider, which cannot exist in a moist atmosphere, 
and against the less persistent forms of scale and 
woolly aphis. Secondly, we may effectually destroy 
the insect by mechanical means, such as wiping 
the leaves with a rag moistened with a soapy 
solution, or, if the insects happen to be large and 
few, by picking them off and destroying them. 
The most common method is by the use of solu- 
tions or powders which, sprayed or dusted over 
the plants, cover the insect’s body, close up its 
breathing pores, and suffocate it. It is the oily, 
spreading nature of the various forms of kerosene 
emulsion that makes them useful in this work. 
One other way to effect this same result, 7. ¢., 
suffocation, is to fumigate the house wherein the 
pests are growing with some powerful gas. This 
is the means by which San José scale is destroyed, 
both in greenhouses and on nursery stock before 
shipment, and when imported from foreign 
countries. 
Among the insect enemies that especially 
bother vines, one of the hardest to deal with is the 
