290 



THE AGRICULTURAL NEWS. 



September 19, 190«. 



been found that when Paris green-' was used as a spray 

 nt ordinary strength (1 It), to 100 gallons of watir), the 

 gyp^y moth caterpillars were not killed, and when the 

 strength of the mixture was increased, the foliage of 

 the trees was injured. Lead arsenate completel}' 

 replaced Paris green in this work as soon as it was 

 found that when the arsenate was used at ordinary 

 strength the cat' ■ pillars were killed, and that whatever 

 the strength at v .lieh it was apjilied, it did not injure 

 the H)liage on wliich it was sprayed. 



'J'here are several advantages to be expected from 

 the use of lead arsenate in combating the cotton 

 worm. The fact that, as already stated, this substance 

 ■does not injure the foliage of plants is of C(jnsidi-rable 

 importance. Lead arsenate also has a \ery great 

 power of adhesion to the leaves of plants, and this is 

 one of the greatest inducements to its use. It will be 

 found that after the lapse of two or three hours of sun- 

 shine from the time of application, only a very little 

 of the arsenate would be washed from the leaves by 

 a really heavy shower. 



On the other hand, there are (-eitaiii features that 

 are likely to seem disadvantageous when considered 

 from the point of view of the planter. In the hrst 

 place, lead arsenate, up to the present time, has been 

 sold only in the form of a heavy paste, and can be 

 applied only .is a spray. This necessitates the purchase 

 •of machines, in place of the bags and tin dusters, which 

 have been used for the application of dry Paris green. 

 Secondly, lead arsenate is much slower in action than 

 Paris green. This is likely to be a disadvantage which 

 will be severely felt unless a very sharp look-out is 

 kept for the first appearance of the cotton worm. In 

 past seasons it has happened frequently that the 

 •cotton wortu has not been noticed until man}' of the 

 caterpillars were full-giown. In such a case, as every 

 cotton grower well knows, it is very diHicult to prevent 

 damage to plants even by the most promi)t application 

 of Paris green. 



It will probably be found best to spray at regular 

 intervals to ensure that a sufticient amount of poison is 

 always on the plant, and especially to enstire tiiat the 

 young leaves are protected as they develope. 



The form of sprayer most in favour with the cotton 

 planters of Barbados is the 'Auto-Spray,' which is a com- 

 pressed air s|)rayor. That is, the air is pumped into 

 the tank until sufficient pressure is obtained, and the 

 spray mixture is forced through the nozzle until the air 

 pressure is entirely reduced. By careful trial, the 

 amount of spray material in the cylinder and the amount 



of pressure may be so adjusted, that one pumping wiiJ 

 serve to force out all the spray nuxtuse. 



In this connexion, another disadvantage in the u»e 

 of leail arsenate is likely to be noticed. This material is 

 very heavy, and a considerable amount of agitation is 

 necessary to prevent the poison from settling to ti^e 

 bottom of the sprayer and thus producing an unequal 

 distribution. Whether it will be po.ssible to get the 

 labourers to agitate the mixture sufficiently by shaking 

 the sprayer as they walk, so that the jjoison may be 

 equally distributed throughout the entire operation 

 of spraying, remains to be seen. The fact, however, 

 that good results in the use of lead arsenate have 

 already been obtained at Barbados, would seem to indi- 

 cate that this is not an insurmountable obstacle. 



One of the points of comparison between dusting 

 andspraying has reference to the weights of the materials 

 used. In dusting with Paris green and lime at the rate of 

 one to six, it will be seen that in applying each pound of 

 the poison, a total of 7 tb. of material has to be handled by 

 the labourers, while in spraying at the rate of 1 ft. of 

 lead arsenate to 100 gallons of water, the material used 

 will have a total weight of nearly 1,000 ft. These 

 figures may be taken to represent the amounts used 

 per acre per application. 



In addition to this, the value anil weight of the 

 respective apparatus used in the application of the 

 spray and of the dust are t-u be taken into considera- 

 tion. The cloth bag used in the application of Paris 

 green costs only a few (;ents and has very little wei>-'l,t, 

 while each sprayer weighs several pounds, and repre- 

 sents an initial cost of several dollais. 



Pans grei'ti usually costs slightly more per pound 

 than lead ansenate, but since it is customary to use 

 a little more of the latter sulistance than of Paris 

 green, the difference in the Hrst cost of the two 

 materials is very small. li\ howe\er, the lead arsenate 

 proves, as is expected, to he much more adhesive than 

 Paris green, the saving of several applications, and the 

 more continuous protection to the plants, due to the 

 lasting properties of the lead arsenate, may make this 

 a much rhea{)er insecticide in the long run. 



It may be added that during the present season 

 one firm of manufacturing crhemists in the United States 

 has succeeded in producing a good grade of lead arsen- 

 ate in a dry powdered form. This has been tried by 

 the Crop Pest Commission of the State of Louisiana in 

 certain of their experiments and the results are very 

 promising. A small quantity of this material will be 

 imported by the Imperial Department of Agriculture 

 for trial. 



