| ) 
| The use of this dust mixture is practical in greenhouses, because — 
| the foliage can be easily and quickly covered with the arsenical with- 
| 
| 
| i 30 BULLETIN 1357, U. S. DEPARTMENT OF AGRICULTURE 
| 
| 
out being injured or disfigured by it, and the sulphur in it also | 
operates ‘against mildew and black spot. Eight pounds of the dust 
ean b> applied to 3,000 plants 2 to 8 feet tall in less than eight — 
1 minutes. Because of its relatively nonsticking quality, the dust 
| covering is washed from the foliage and must be renewed after each 
| syringing, or about two or three times a week. By this means the 
| new crowth produced in the periods between dusting is also’ k>pt 
| covered. From the middle of February, when the “beetles begin 
feeding, until November, when they become inactive, the 1 aves must 
be constantly covered with an arsenical to protect them from i injury. 
It was not possible to determine with accuracy the effect of th-se 
| dusts when applied on a commercial scale in the greenhouses, unless 
| | diminution of numbers be used as an index. The results presented 
| 
| in Table 13, however, 
| indicate the effect of 
various mixtures on 
caged beetles. 
The outstanding 
fact in the cages 
where — arsenicals 
were used is the very 
greatly reduced 
amount of feeding as 
compared with the 
fohage consumed in 
the check cages, and 
this indicates a re- 
pellent action in ad- 
dition to the poison- 
ig. 15.—Bellows type of hand duster, usefui for apply- On eB S0 oer 
ing insecticidal dusts in greenhouses th in larger quantities. 
- In some cages the 
arsenicals seem to affect the beetles almost immediately, whereas 
in others the action appeared to be prolonged over several days. The 
amount of feeding on leaves dusted with superfine sulphur was some- 
what reduced, but did not result fatally. There was no evidence 
that the effectiveness of dusts would be increased by the addition of 
cornstarch as a possible bait. Hellebore proved valueless. Beetles 
which were caged with untreated rose leaves ate voraciously, while 
others confined without food remained alive from 7 to 15 cays. 
In three establishments which had suffered severe injury dusts were 
apphed during three seasons. In two of these places the plants were 
treated persistently and thoroughly with a mixture of lead arsenate 
and sulphur (10 per cent formula) during the periods when the 
beetles were present in large numbers. Although many of these in- 
sects were actually removed by tearing out infested beds, by replac- 
ing the soil, by setting new plants, and by hand picking, the dusting 
was undoubtedly a very important factor in reducing the infestation 
in these establishments. 
