﻿28 



BULLETIN 1357, U. S. DEPARTMENT OF AGRICULTUEE 



SPRAYING WITH ARSENICALS 



Ordinarily arsenicals used as stomach poisons are the standard 

 remedies applied in combating such ravenous leaf feeders. For 

 this reason preliminary tests were made with varying- strengths of 

 calcium arsenate, arsenate of lead, and Paris green. In sprayino- 

 the plants at Alexandria, Va., with a pressure sprayer, special 

 care was taken to cover all of the foliage so that it presented a 

 whitewashed appearance which lasted many days. The arsenates 



of lead and calcium did not injure 

 the rose foliage when used at the 

 rate of from 2 to 21/2 pounds to 50 

 gallons of water, to which one-half 

 ounce of soap was added for each 

 gallon of spray material, provided 

 they were applied only on bright 

 days; otherwise severe burning re- 

 sulted. This was demonstrated in 

 experiments conducted later at 

 Oak Lane, Pa., where one block of 

 40 rose bushes sprayed at the fore- 

 going dilutipn on a dark, cloudy 

 day showed severe burning and the 

 plants shed 50 per cent of the foli- 

 age, whereas a similar group 

 sprayed on the following day, 

 which was clear, suffered no injury. 

 In marked contrast with the re- 

 ported control of this insect on 

 strawberry plants by means of 

 spraying with calcium arsenate or 

 lead arsenate, it was found that 

 under the conditions existing in 

 rose houses this treatment was not 

 only im]3racticable and objection- 

 able but was actually ineffective. 

 It was impracticable because the 

 beetles fed at night on the young 

 and tender growth, which was 

 being forced so rapidly during the 

 hot, sultr}^ nights that it could 

 not be sprayed frequently enough 

 to keep the new foliage covered 

 with the poison. Moreover, the 

 whitish deposit which remained 

 on the leaves after spraying was objectionable to the florists, be- 

 cause it reduced the market value of the cut flowers. It was ineffec- 

 tive in controlling the beetles because they avoided feeding on the 

 arsenate-coated foliage but continued to devour the new leaves. 



There is, however, one period in the culture of roses when the 

 use of an arsenical as a spray has proved effective against the 

 beetles. When the rose plants are cut back (fig. 11) practically all the 

 foliage is removed and the fresh growth develops from new buds. 

 The absence of foliage forces the beetles to feed on the green bark 

 as well as on the swelling and breaking eyes or buds, which causes 



Fig. 11. — Rose plant cut back at end of 

 resting period. Many adults were 

 found hiding in the debris on the 

 soil. (See fig. 14) 



