SOLID-STKEAM SPRAYING IN NEW ENGLAND. 11 



SHADE-TREE SPRAYING. 



The spraying of shade trees with arsenate of lead should be ac- 

 complished at as early a date as possible after the foliage has suf- 

 ficiently developed. (PI. XII.) Early spraying not only applies to 

 the gipsy moth, but will poison many brown-tail caterpillars, as they 

 are much earlier feeders than the gipsy moth. In the case of the elm 

 leaf-beetle (GaleruceUa lf<ola Miill.) much is accomplished in pois- 

 oning the adult beetles, which do a small amount of feeding after 

 coming out of hibernation before mating and laying eggs, as they are 

 very easily poisoned at that time. It is often argued that solid- 

 stream spraying on street trees is too expensive and that the work can 

 be done much cheaper with smaller apparatus. The principal reason 

 for this is because of the low first cost of the smaller outfits. (PL 

 XIII. ) This may be true for a single year, but for two or more years 

 the solid-stream method is the cheaper. The total cost of the most 

 expensive high-power apparatus on the market at the present time is 

 approximately $1,500 for a complete equipment. It is safe to figure 

 depreciation at the rate of 20 per cent each year, although there are 

 machines in the field at the present time that have been used 8 

 years and have only required an annual overhauling and the replace- 

 ment of small worn parts. In 20 days' spraying one large machine 

 should treat 10,000 shade trees. This would average only 3 cents 

 for each tree in depreciation which is not prohibitive to any munici- 

 pality. Taking everything into consideration, the entire cost of 

 spraying shade trees with the solid stream does not exceed 12 cents 

 per tree if the work is managed properly. The following figures are 

 submitted to show how the cost per day is computed for 20 working 

 days: 



1 pair of horses and driver $6.00 



3 men, 8 hours each . 7. 50 



560 pounds of poison, at 5 cents per pound 28. 00 



10 gallons of gasoline 1.80 



1 gallon of oil .30 



Depreciation per day at 20 per cent per year 15. 00 



$58.60 



The average number of shade trees sprayed with each 400 gallons 

 of poison is 35, and 14 tanks (5,600 gallons) in 8 hours is a good 

 average, totaling 490 street trees per day, making the average cost 

 per tree about llf cents. In treating shade trees, where any consid- 

 erable amount of spraying is to be done, the use of small outfits in 

 mist spraying is much more expensive than the solid-stream method. 

 In an experiment conducted during the summer of 1916 the cost of 

 treatment with a small hand outfit was more than twice the amount 

 per tree that it was when the solid stream was used. While one can 



