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BULLETIN 1357, U. S. DEPARTMENT OP AGKICULTUEE 



The use of this dust mixture is practical in greenhouses, because 

 the foliage can be easily and quickly covered with the arsenical with- 

 out being injured or disfigured by it, and the sulphur in it also 

 operates against mildew and black spot. Eight pounds of the dust 

 can b3 applied to , 3,000 plants 2 to 3 feet tall in less than eight 

 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 Aveek. By this means the 

 liew growth 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 haves must 

 be constantl}^ covered with an arsenical to protect them from injury. 

 It Avas not possible to determine with accuracy the effect of thzse 

 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 

 Av here arsenicals 

 were used is the very 

 greatly reduced 

 amount of feeding as 

 compared Avith the 

 foliage consumed in 

 the check cages, and 

 this indicates a re- 

 pellent action in ad- 

 dition to the poison- 

 ous effect when eaten 

 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- 

 Avhat reduced, but did not result fatall3^ There was no evidence 

 that the effectiveness of dusts Avould be increased by the addition of 

 cornstarch as a possible bait. Hellebore proved valueless. Beetles 

 Avhich Avere caged with untreated rose leaves ate voraciously, while 

 others confined without food remained alive from 7 to 15 clays. 



In three establishments Avhich had suffered severe injury dusts were 

 applied 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 Avere actually removed by tearing out infestpcl 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. 



Fig. 13. — Bellows type of hand duster, useful for apply- 

 ing insecticidal dusts in greenhouses 



