680 ANNUAL REPORT OF THE Off. Doc. 



scales on treated trees, and the probability of not reaching an accu- 

 rate figure is so large that it may be regarded as an impossibility. 

 For this reason we do not think it possible that an estimation can 

 be made which is within 5 per cent, on either side of the accurate 

 figure, and any estimation carried out to the fractional part of one 

 per cent, it little else than an absurdity. 



A third serious mistake is where trees are not thoroughly sprayed. 

 In this case the insecticide is not given a fair chance, as where 

 parts of trees are missed breeding centers are established for the 

 next season. From these centers the entire tree may soon become 

 entirely re-infested, with the result that the insecticide is marked 

 as "worthless," yet it may have killed every scale that it touched. 



Another mistake, although not so common as the others, is where 

 trees are sprayed for an insect with which it is not infested, for 

 it must be understood that no spraying should be done merely for 

 the sake of "spraying," especially with an insecticide which has an 

 oil for its base, as the oil is bound to injure and can do no possible 

 good where the tree is not infested, and consequently will be a 

 waste of material and labor as well as injury to trees. 



As to the effect on the tree, it is absolutely necessary to note the 

 condition of the tree previous to treatment. Here again the insecti- 

 cide is often blamed for something which it does not do, as many 

 times the trees are nearly dead before they are sprayed, and may 

 be so far gone that even the most efficient spraying could not save 

 them, any more than a physician can save a dying man. 



In the item of cost is where we find our first great objection to 

 Commercial Insecticides, as when applied in a strength sufficiently 

 strong to be effective we find that the cost is too great for the 

 use of many fruit growers. The second objection to them is their 

 general inefficiency. 



Commercial Insecticides on the market at the present time may 

 be roughly grouped in the following classes: 



(1) Those having crude oils for a basis, which are rendered soluble 

 by some "secret" means, as "Scalecide," "Target Brand Scale De- 

 stroyer," etc. 



(2) Modification of the Lime-sulphur-salt solution, as "Con Sol," 

 and "Horicum." 



(3) Partial union of 1 and 2, as "Kill-O-Scale," and "Salimene." 



(4) By-products of no other use, and for that reason often recom- 

 mended by the originators as the "only insecticide and fungicide 

 in the world." Some of the last-named compounds have proven 

 to be such as Calcium Sulphate, one of the most insoluble compounds 

 known to chemistry, a paint mixture, which would not kill even 

 the Aphids, and many others too numerous to mention, but all of 

 about the same value as the two just mentioned above. 



Early in July Professor Surface outlined and the writer under- 

 took a series of experiments to determine the possibility of spraying 

 during the summer months and hold the scale in check to such an 

 extent as to warrant summer spraying. In these experiments com 

 mercial insecticides were mostly used, and the results are summar- 

 ized below: 



In cases where "Con Sol," "Target Brand Scale Emulsion," and 

 "Kil-O-Scale" were applied in summer strength as recommended by 

 the manufacturers, we found that they caused the crawling larvae 



