THE PEAR LEAF-WORM. 21 



WASHINGTON EXPERIMENTS. 



In Washington State, where the pear thrips is not to be considered, 

 lead arsenate would appear to be the only logical insecticide to 

 be used against the pear leaf -worm. It is less expensive than extract 

 of tobacco sprays, and easier to mix than oil sprays; besides, the 

 lead arsenate can serve a double purpose — that of controUing this 

 worm and, at the same time, the codling moth. The first apphcation of 

 lead arsenate for the control of the latter is made when the petals of 

 the pear blossom drop, and at this time the larvae of the sawfly have 

 reached the second instar. The injury done previous to this is 

 neghgible ; it is only during the last two instars that the larvae cause 

 serious injury to the foliage. 



Mr. Zimmerman, in whose orchard the worst infestation occurred, 

 used lead arsenate at the rate of 4 pounds to 100 gallons of water 

 against the pear leaf-worm with excellent results, both in 1914 and in 

 1915. The first year there was a very severe infestation of larvae 

 and the apphcation was made May 16, at the same time that the first 

 codling-moth spray was applied to apples; this was too late for the 

 pears, as the larvae already had devoured as much as a third of many 

 of the leaves. However, it saved most of the trees from a severe 

 defoliation, as is shown in Plate II, which pictures a tree of which 

 the left half was sprayed while the right half was left unsprayed, the 

 photograph having been taken on May 21,5 days after the trees were 

 sprayed. The difference was very marked. No definite coimt was 

 made, but on the sprayed trees scarcely any living larvae could 

 be found, while many limp and blackened remains were hanging 

 from the partially eaten leaves. In the unsprayed portion of the 

 tree just mentioned, which served as a check, larvae were numerous, 

 and large numbers of them were dropping to the ground to spin their 

 cocoons. 



In 1915 the infestation was not so severe, owing to the control 

 measures of the year before. The orchard was sprayed on May 6, 

 earlier than in 1914. Lead arsenate was used at the same strength 

 as before, that is, 4 pounds to 100 gallons of water. This applica- 

 tion effectually checked the ravages of the larvae, and the trees suffered 

 very little injury. 



In 1915 a small experiment was performed with nicotine sul- 

 phate, 40 per cent concentration. Infested twigs wore placed in 

 water and sprayed with a hand pump. April 27 a twig with 10 second- 

 instar larvae was sprayed with the nicotine sulphate at the rate of 

 1 to 1,200, with the addition of a little fish-oil soap. On April 28 

 the twig was examined and all the larvae found dead. The larvae 

 on a check twig were still alive. On this date a similar twig was 

 sprayed in the same way, except that the nicotine sulphate was- 



