14 
‘abbage, dusted as recommended above, 28 heads would have to be 
eaten at one meat to reach this result (Gillette). It is preferable, 
however, to use other insecticides in the case of vegetables soon to be 
eaten, and thus avoid all appearance of danger. 
INSECTICIDES FOR EXTERNAL SUCKING INSECTS (CONTACT 
POISONS). 
The simple remedies for this class of insects, such as soap, insect 
powder, sulphur, tobacco decoction, ete., are frequently of value, but 
need little special explanation. Some brief notes will be given, how- 
ever, describing the methods of using some of these substances which 
are easily available and will often be of service, particularly where 
few plants are to be treated. The standard remedies for this group 
of insects, viz, crude petroleum, kerosene, and kerosene emulsions, 
resin washes, lime, sulphur, and salt wash, hydrocyanic-acid gas, and 
vapor of bisulphide of carbon, will be afterwards treated in the order 
mentioned. 
SOAPS AS INSECTICIDES. 
Any good soap is effective in destroying soft-bodied insects, such as 
plant-lice and young or soft-bodied larve. As winter washes in very 
strong solution, they furnish one of the safest and most effective means 
against scale insects. The soaps made of fish oil and sold under the 
name of whale-oil soaps are often especially valuable, but variable in 
composition and merits. A soap made with caustic potash rather than 
with caustic soda, as is commonly the case, and not containing more 
than 30 per cent of water, should be demanded, the potash soap yield- 
ing a liquid in dilution more readily sprayed and more effective against 
insects. The soda soap washes are apt to be gelatinous when cold, and 
difficult or impossible to spray except when kept at a very high 
temperature. 
For plant-lice and delicate larvee, such as the pear slug, a strength 
obtained by dissolving half a pound of soap in a gallon of water is 
sufficient. Soft soap will answer as well as hard, but at least double 
quantity should be taken. 
As a winter wash for the San Jose and allied scale insects, whale-oil 
or fish-oil soap is dissolved in water by boiling at the rate of 2 pounds 
of soap to the gallon of water. If applied hot and on a comparatively 
warm day in winter, it can be easily put on trees with an ordinary 
spray pump. On avery cold day, or with a cold solution, the mix- 
ture will clog the pump and difficulty will be experienced in getting it 
on the trees. Trees should be thoroughly coated with this soap wash. 
Pear and apple trees may be sprayed at any time during the winter. 
Peach and plum trees are best sprayed in the spring, shortly before the 
buds swell. If sprayed in midwinter or earlier, the soap solution 
