CONTROL OF CODLING MOTH IN COLORADO. 7 



In the treated plats over 90 per cent of the worms actually infesting 

 the fruit gained entrance through the side of the apple and less than 

 7 per cent entered by way of the calyx. In untreated plat X 72.31 

 per cent of the larvae entered through the side of the fruit and 26.45 

 per cent through the calyx end. It will thus be seen from these data 

 that one of the chief difficulties in controlling the codling moth in the 

 Grand Valley of Colorado is to prevent the larvae from entering the 

 apple through the side. 



In the plats where arsenate of lead was employed the average 

 number of larvae for worm-infested fruit varied from 1.39 to 1.67, 

 whereas in the .arsenate of lime plats this average was increased to 

 1.86 and 2, and in the unsprayed plat there was a further increase to 

 2.08 larvae for each wormy apple. The higher the percentage of 

 apples free from worms the lower the average number of worms per 

 apple. Thus in plat III, where the best control was obtained and 

 where 72.22 per cent of apples were free from worms, there was an 

 average of only 0.39 larva per apple, and in plat X, which was un- 

 sprayed and yielded but 13.51 per cent of worm-free fruit, there were 

 1.80 larvae per apple. 



In scoring results, account was taken of the so-called codling 

 moth ''sting" (PI. II). The sting is a shallow excavation extending 

 through the skin of the apple into the flesh to a depth of about one- 

 sixteenth to three thirty-seconds of an inch. It is caused by newly 

 hatched larvae that only succeed in eating their way through the 

 skin before succumbing to the poison, or, for other reasons, do not 

 penetrate deeper into the fruit. In the sprayed plats the average 

 number of stings per apple varied from 0.82 to 1.91, whereas in the 

 unsprayed plat the average was only 0.12. 



It is the belief of the writers that, with a uniform infestation and 

 crop and with other factors equal, the number of stings is directly 

 proportional to the number of worm-free apples. In other words, 

 if the spray treatment is effective, the only indication of worm attack 

 will be found in the sting marks, and these will increase within 

 certain limits as the number of worm-free apples increases. In the 

 case of unsprayed fruit, the worms are not subjected to a poison, 

 and hence what might result in only a sting in a sprayed apple 

 becomes a worm hole in the untreated fruit. It should not be 

 inferred, however, that unsprayed fruit is totally devoid of stings, 

 for sting marks sometimes occur on untreated fruit and may be 

 accounted for by larvae which start an entrance hole and then change 

 to another place, or by Inrwe that, before penetrating very far into 

 the fruit, are blown ofl' by wind, ])rushed off by foliage, or washed off 

 by heavy rains. 



SPRAYING EXPERIMENTS IN 1916. 



In 1916 the Gus J. Johnson orchard, at Highland Park, and the 

 J. D. Nettleton orchard, at Fruitvale, were used for experimental 

 purposes. 



