388 INSECTS AFFECTING VEGETATION 



It is important that the water be put in the vessel first, then the 

 acid, and lastly the cyanide. If the water and cyanide are put in 

 the vessel first and the acid poured in afterwards, there is danger of 

 an explosion which will scatter the acid and burn the tents and the 

 operator. In the spring, when the trees are tender with new 

 growth, and in early fall when the oranges are nearly grown and 

 the skins are likely to be easily marred, and also with young trees, 

 it is advisable to add one-third more water than ordinarily used, 

 or to add the cyanide in larger lumps. This causes the gas to gen- 

 erate more slowly and with less heat, and, if the tents are left over 

 the trees a third longer, the effectiveness of the treatment will not 

 be lessened. The person handling the chemicals should always 

 have an attendant with a lantern, to hold up the tent and enable the 

 cyanide to be quickly dropped into the generator, and to facilitate 

 the prompt exit of the operator. 



Trees are fumigated for the black scale in southern California 

 in October, or preferably in November. The red and other scales 

 may be treated with gas at any time, but preferably at the season 

 already indicated. In California most of the work is done by con- 

 tract, or under the direct supervision of the county horticultural 

 commissioners, in some cases the tents and material being furnished 

 at a merely nominal charge, together with one experienced man to 

 superintend the work, while a crew of four men operate the tents, 

 the wages of the director and men being paid by the owner of 

 the trees. 



Construction and Handling of Tents.* The tents now em- 

 ployed are of two kinds, the sheet tent of octagonal shape for large 

 trees, and the "ring" tent for trees under 42 feet in height. The 

 ring tents, or, as they are also called, the bell tents, are bellshaped 

 and have a hoop of half-inch gas pipe fastened within a foot or so 

 of the opening. Two men can easily throvy one of these tents over 

 a small tree. An equipment of 36 or 40 ring tents can be handled 

 by four men. They are rapidly thrown over the trees by the crew, 

 and the director follows closely and introduces the chemicals. By 

 the time the last tent has been adjusted the first one can be removed 

 and taken across to the adjoining row. An experienced crew, with 

 one director, can treat 350 to 400 5-year-old trees, averaging 10 feet 

 in height, in a single night of eleven or twelve hours. The cost 

 under such conditions -averages about 8 cents a tree. 



With large trees the large sheet tents are drawn over them by 

 means of uprights and pulley blocks. Two of these sheets are ne- 

 cessary for very large trees, the first being drawn halfway over and 

 the second drawn up and made to overlap the first. In the case of 

 trees from 24 to 30 years old and averaging 30 feet in height, about 

 50 can be treated in a night of ten or twelve hours with an equip- 

 ment of 12 or 15 tents, the cost being about 75 cents per tree. It is 

 not practicable to treat trees above 30 feet in height. 



The handling of the bell tents is simple and needs no further 

 description, but the large tents are not so easily operated, and the 

 method of adjusting the great flat octagonal sheets over the trees, 



* For illustrations, see pages 87, 104, 384. 



