1920.] PUBLIC DOCUMENT — No. 31. 35a 



the main had not been tested. Accordingly, experiments on 

 control measures were at once begun. 



The materials tested were repellent and insecticidal dusts, 

 contact insecticides, and arsenical sprays and dust. The re- 

 pellent and insecticidal dusts proved worthless, partly, perhaps, 

 because of the habit of the caterpillar, when disturbed, of 

 dropping to the ground, but mainly because it was practically 

 impossible to cover the under surfaces of the leaves where 

 most of them feed. Contact insecticides also failed, the plants 

 in most cases being so closely matted together that the cater- 

 pillars could not be reached by the sprays, and when the plants 

 were parted the insects dropped to the ground, as already 

 stated. 



Calcium arsenate, magnesium arsenate and lead arsenate 

 were used as sprays. These poisons, sprayed onto the leaves, 

 would be consumed by the insects when they ate through to the 

 upper surfaces, so the poison could be sprayed onto the plants 

 without disturbance, and left for the caterpillars to eat when 

 they got to it. As the insects after a short time eat entirely 

 through the leaves, this placing of the poison was effective. 

 The calcium and magnesium arsenates burned the foliage so 

 badly, however, that their value as insecticides was less than 

 the injury they caused. Lead arsenate gave entire success, 

 particularly if applied before the leaves had been badly riddled. 

 The only drawback to its use was in cases where the pods 

 were nearly ready for picking. In such cases the only way of 

 handling proved to be to thoroughly wash the beans gathered 

 after treatment, to remove the poison which had fallen on 

 them. 



Arsenate of lead powder, dusted onto the leaves, was also 

 effective against the insects, but proved difficult to apply 

 evenly with any of the dusting machines, and where it was 

 too thick it injured the leaves. 



Generations of the Codling Moth. — Whether the second 

 generation of the codling moth is sufficiently important in 

 Massachusetts to require a special late treatment has for years 

 been a question. It now seems probable that it is not often 

 large enough to need consideration. L^ncertainty as to the 

 best time for the second spring spraying for this pest has led 



