356 GROWTH OF PLANTS 



Weighings of samples of 100 leaves were made from American elm trees 

 in 1934 and again in 1935 as compared wth an equal number of unhanded 

 trees. The difference in leaf weight resultmg from banding was less than 

 10 per cent, indicating no appreciable control. 



Since cankerworm larvae had occurred on banded trees in numbers 

 sufficient to defoliate them in spite of the fact that neither in the fall nor 

 in the spring were any female moths observed that had succeeded in crawl- 

 mg over the bands, the larvae apparently had infested the banded trees by 

 some other means than by hatching from eggs laid above the bands. 



It was decided to investigate the possibility that the infestation on the 

 banded trees had been brought about by larvae being blown by the wind 

 from unhanded trees. Eight stationary shields covered with tanglefoot and 

 directed toward the cardinal and intercardinal points of the compass were 

 erected on a pole 20 feet high just north of the banded area. From time to 

 time the shields were exammed for the presence of cankerworm larvae and 

 the tanglefoot renewed when needed. The site selected was a clear space 

 where no larvae could reach it except by passing through an ah space of 

 at least 25 feet. A tanglefoot barrier was maintamed on the pole to pre- 

 vent any larva from climbing up from the ground. To the west, the land 

 sloped away rapidly and there were no infested trees m direct line of the 

 shields for about 500 feet. It was demonstrated by means of captures on 

 the tanglefoot shields that cankerworm larvae are dissemmated by mnd. 

 A total of 99 larvae were collected on the shields. Larvae were collected on 

 all shields. Toward the west and the northwest there were no mfested 

 trees nearer than 500 feet, yet more than 20 per cent of the larvae were 

 collected from shields facing these directions. It was estimated that if the 

 density of the larvae per cubic foot of air space was the same at all heights 

 above ground as surrounding the shields, in an air space occupied by a tree 

 60 feet high and 20 feet wide approximately 5000 larvae would have drifted 

 from May 18 to June 12 during the period of observation. 



As is often the case in research, the failure of an accepted method led to 

 a discovery, namely that cankerworm larvae are wind-borne, the silk 

 strands buoying the insects through the air like parachutes. 



Japanese beetle. i3,i3'-Dichloroethyl ether was tested as a soil fumigant 

 against the larvae of the Japanese beetle (Popillia japonica Newm.). The 

 saturated aqueous solution, with the addition of 0.1 per cent Tergitol 7 

 penetrant * (a sodium alkyl sulphate) as wetting agent, was found to give 

 satisfactory control of the grubs, when two applications were made about 

 one week apart when the grubs are near the surface of the soil.^" No injury 

 to the turf resulted with this treatment. When it is desired to avoid the 

 use of materials which leave poisonous residues, such as lead arsenate, and 

 where a rapid kill is required, this mixture may offer a promising substitute. 

 It was found, however, that iS,i3'-dichloroethyl ether with Tergitol 7 

 penetrant as a wetting agent was not very effective in the control of adult 

 * A product of Carbide and Carbon Chemicals Corporation, New York, N. Y, 



