COMBINED SPRAYS FOR CONTROLLING INSECT PESTS. 
'* The reasons for combining insecticides and fungicides, however, may 
be sufficiently urgent as to justify the action, e.g.:— 
(1) Although plants are often attacked independently by fungi, 
bacteria, or insects, these may, and often do, work in’ combination. 
(See Sc. and Ind., Nov., 1920, p. 652, on the “ Role of Insects in the 
Dissemination of Diseases’) In such cases a combined spray may be 
of decided value. ; ; rly ; 
(2) In places where there is a great shortage of labour and also 
where spraying materials are expensive, a combined spray would be 
preferred. 
(8) Under various state laws relating to spraying for the control 
of orchard pests and diseases, ¢.g., for codling moth and fruit fly, &c., 
the grower is compelled to carry out a certain minimum number of 
sprayings with specified substances (mostly arsenate of lead of an 
approved brand). He may,.therefore, combine other substances with 
that required by law in order to reduce to a minimum the number of 
sprayings that he would find it necessary to’ give in order to keep 
all pests under control. 
(4) In response to demand, scientists have investigated the results 
of combining two or three spraying materials, and many- experimental 
spraying or dusting tests have been conducted in orchards and elsewhere 
under appropriate control. Consequently, the grower can now obtain 
- adyice ou what to mix and what not to mix, the precautions that he 
must exercise, and the results that he can expect, from the use of his 
mixture. 
Tn combination sprays, each substance should be selected for definite 
reasons, ¢.g., in spraying peach trees one application of Bordeaux at 
the correct time is sufficient to prevent practically all damage from 
peach leaf curl (Haoascus deformans). At the same time arsenate of 
lead may be added for peach tip moth. The same mixture is very 
efficient as the first spray (pink bud stage) for apple diseases and 
*insects. The lead arsenate also complies with the requirements of the 
law. In all cases when selecting insecticides it is necessary to dis- 
tinguish between biting insects and sucking insects. The former (e.g., 
beetles, grasshoppers, caterpillars, wireworms, and cut worms) have 
their mouth parts developed for biting and chewing plant tissues; the 
latter (e.g., aphids and other plant lice, mites, and bugs) have their 
mouth parts developed as a sucking tube which enables them to pierce 
the outer coatings of the plant cells and to suck the juices from the 
internal tissues. Biting and chewing insects can be killed by means 
of poisons placed on the surface of the plant. When the insects feed 
on the leaves, the poison is eaten with the food, and acts through 
absorption in the stomach and intestinal tract. The sucking insects 
are killed by contact insecticides. These generally contain volatile 
substances, and death is mainly due to their absorption into the tissues 
of the insects. It was formerly thought that death was due to suffoca- . 
tion by the stopping of the breathing pores or the closing of the 
trachew. Recently, however, investigations indicate that insects aré 
not so readily suffocated, and that the volatile parts of kerosene, nico- 
tine, carbon disulphide, pyrethrum, &c., are effective long before the 
C.21662.—3, 721 
