32 BULLETIN 1238, U. S. DEPARTMENT OF AGRICULTURE 



initial observation has never been verified. Di\ H. E. Ewing, of the 

 Bureau of Entomology, states that this species is unrecognized, and 

 that the habit of sucking eggs, if it occurs, is contrary to the habits 

 of the group to which the genus Nothrus belongs. 



CONTROL MEASURES. 



Three general methods have been recommended and used for the 

 control of cankerworms: Cultivation, spraying, and the use of 

 mechanical barriers to prevent the ascent of the wingless female 

 moths and the larvae. 



CULTIVATION 



Plowing and cultivation at any time when the spring cankerworm 

 larvae or pupae are in the ground will aid materially in their control 

 by exposing them to many of their enemies. This practice, however, 

 will have little effect on the fall species, which is safely inclosed in a 

 tough cocoon. 



SPRAYING. 



The present practice of spraying for the codling moth and other 

 insects has almost eliminated the cankerworm as a pest in well- 

 cared-for orchards. 



Laboratory tests have shown that the larvae of both species are 

 readily killed by arsenate of lead, applied at the strength of 1 pound 

 of the powdered form in 50 gallons of water. In all tests made in 

 the laboratory at Wallingford, even the last-stage larvae died within 

 four or five days after being placed on sprayed foliage, and the 

 earlier stages were killed in a shorter time. 



Although the larval feeding period of the cankerworms is short, 

 it occurs at such a time that the first two of the regular summer 

 spray applications recommended for the apple orchard will be ef- 

 fective. Peck (If) noted that the eggs " commonly hatched about the 

 time that the red currant is in blossom, and the apple tree puts forth 

 its tender leaves." In Wallingford the greater part of the hatching of 

 the eggs of the fall species has invariably occurred during the period 

 when the apple blossoms of medium-season varieties were showing 

 pink, and was practically completed before the blossoms were open. 

 The eggs of the spring species began to hatch in 1920 a day or two 

 later than those of the fall species, and the hatching period was 

 somewhat more prolonged. It is therefore evident that if the so- 

 called pink spray includes an arsenical, and is thoroughly applied, 

 the newly hatched larvae of both species will find awaiting them a 

 meal of poison. This application is the more important of the two 

 noted, and in case of a severe infestation should never be omitted. 

 If an outbreak occurs in young orchards not in bearing, an applica- 

 tion of arsenate of lead should be made shortly after the proper time 

 for the pink spray on bearing trees, at which time all the eggs will 

 have hatched, but comparatively little feding will have been done. 

 Observations in an orchard near Wallingford during the season of 

 1920 confirmed these recommendations. The orchard in question 

 had been totally neglected for a number of years, and had become 

 thoroughly infested with the spring cankerworm. In 1920 the 

 owners applied the pink spray, but were a few days late about it, al- 



