34 FIFTH REPORT OF THE ENTOMOLOGICAL COMMISSION. 



effective against the insect, but that this poison injures the plant more than does the 

 London purple. 



Three-fourths of a pound of Paris green to a barrel (36 or 40 gallons) of water, with 

 3 quarts of flour, may be regarded as a poison mixture of medium or average strength 

 for treating elms against these beetles, and the indications thus far are that the 

 amount of Paris green should not be increased above one pound or be diminished much 

 below one-half a pound in this mixture. To a bucketful of water three-fourths of an 

 ounce of Paris green may be used. The action of this poison is slow but severe, and 

 varies much with the weather. Thus far the results of tests have been varied so much 

 by the weather and different modes of preparation and application that they will be 

 repeated. When used strong enough to cauterize the leaves the poisonous action 

 upon the plant may be observed to continue for several weeks. 



The species of Ulmus are quite susceptible to the effects of poison, 

 perhaps as much so as any common species of forest tree. But little 

 can be added to the above quotation, as there are few experiments re- 

 corded concerning work of this kind on other forest trees. With fruit 

 trees and vines there is a large experience, and the results indicate 

 that either of these arsenicals can be safely used on the most tender 

 plants in proportion of 1 pound to 100 gallons of water, if properly 

 atomized. Strong, hardy plants readily stand a strength of 1 pound 

 to 50 gallons of water, if applied with proper care. It is safe to con- 

 clude that between these two limits a strength suitable for all plants 

 may be obtained. 



A thoroughly atomized weak mixture will, under favorable con- 

 ditions, prove as efficient as the stronger ones ; but in wet, showery 

 weather weak applications are more liable to be washed off. 



Properly atomizing the liquid is of the greatest importance, for only 

 by this means can all the foliage be reached. The even distribution 

 thus obtained enables the leaves to retain a greater amount of the 

 poison with less injury than when sprayed in coarse drops. 



Insecticides which act by contact. — This class of remedies 

 apply principally to non-masticating insects, i. e., those which take 

 their food through a sucking-tube or proboscis, such as the plant- 

 bugs, aphids, and scale insects. , They may, however, often be suc- 

 cessfully applied to soft-bodied mandibulate insects, in lieu of the 

 poisonous mixtures. 



There are a great variety of substances, such as alkaline washes 

 and powders, and preparations of oils, and particularly the products of 

 petroleum, which have been successfully used on insects affecting 

 roots, trunks, branches, and foliage of trees. The experimental data 

 concerning them have been mostly obtained from cultivated fruit trees 

 and vines, but they will prove equally available against the similar 

 enemies of forest trees. 



Wood Ashes and Lime. — Of alkaline powders, wood ashes and slaked 

 lime are commonly used either pure or in mixtures around the bases of 

 trees or interred in the earth among the roots of plants to destroy root 

 aphids or other insects affecting the roots. No definite instructions 

 concerning their use can be given, as both substances vary as to strength, 



