May 1, 1921. 



THE INDIA RUBBER WORLD 



555 



Rubber Tents in Tree Fumigation 



Attempts to Control an Annual Loss of More Than a Billion Dollars by a New Use of Rubber 



FEW REALIZE the Constant fight that fruit growers and indeed 

 all agriculturists wage against pests of a thousand and one 

 kinds. Scale and boll-weevil are but two out of scores of 

 common enemies that sometimes wipe out huge plantings. Gas 

 fumigation, already practiced upon a large scale, has proved a 

 wonderful success. And furthermore, the rubber, gas-tight, fum- 

 igation tent has arrived; and growers cf oranges, lemons, grape- 

 fruit, and other citrus fruits, are predicting that it will soon sup- 

 plant the old-time canvas covers, under which scale and other 

 pests have been quite generally killed. 



EVOLUTION OF THE RUBBER TENT 



For twenty years the growers have snught in various ways 

 to check one of 

 the greatest 

 drawbacks of the 

 tent method — 

 gas leakage 

 through the cot- 

 ton fabric ; but 

 even the applica- 

 tion of a muci- 

 lage from boiled 

 down cactus 

 leaves mixed 

 with linseed oil, 

 as tried in the 

 Southwest, has 

 failed to make 

 the fabric im- 

 permeable to the 

 confined fumes. 

 As the fumigant 

 has to be used 

 from one to three 

 times a year, the 

 item of leakage 

 of valuable gas 

 becomes impor- 

 tant. Some growers discouraged by the cost, the trouble of tent 

 erection, and the fact that fumigation had to be carried on almost 

 entirely at night, even turned back to the -dinost discarded method 

 of spraying with dry and liquid insecticides. 



.An alert rubber man, George Hockensmith, an e.\pert on balloon 

 fabrics, had been studying the troubles of the citrus growers and 

 he intimated several months ago to Professor H. J. Quayle, en- 

 tomologist of the University of California Experimental Station 

 of Riverside, California, that he could help to solve one of the 

 growers' most trying problems, gas leakage. Encouraged by the 

 entomologist. Mr. Hockensmith tried various kinds of materials 

 and finally decided that a fabric, equivalent in strength to 8-ounce 

 U. S. .Xrniy diirk would best serve the purpose. 



FABRIC TREATMENT. TENT CONSTRUCTION AND TESTS 



The treatment given the material is similar to that which was 

 given to balloons and dirigibles manufactured during the war, the 

 fabric being not only rubberized and made perfectly gas-tight, but 

 also given an aluminum color facing that makes the tent also 

 , opaque. The advantage of opacity is that fumigation may be 

 carried on in the tents three or four hours before sundown. Ex- 

 perience with the plain canvas tents has proved that day fumiga- 

 tion gives decidedly inferior results to night work. For some 

 reason not yet explained, sunlight on i lain canvas tents during 

 the fumigation of trees with liquified hydrocyanic-acid gas often 

 causes peculiar injury to fruit and leaves. Hence the practice 



Placing Rubber Gas-Tight Tent Over Orange Trees 



of doing most of the "gassing" after sundown. It is claimed 

 that the new rubberized cloth tent will efifectually bar out the 

 actinic sun rays which are believed to do the mischievous work 

 with the gas, thus making the long-desired daylight fumigation 

 feasible. 



The new rubber tents are octagonal in .shape, the center being 

 made of the heavy material and the wings or sides of a coated 

 fabric about three ounces lighter to the yard. Such construction 

 not only makes the tent lighter, but also more convenient to 

 handle in the field. As might be expected, the initial cost of the 

 rubber tents is more than that of the plain canvas affairs, but the 

 a{l\antages of the rubber tree cover are so great, it is 



claimed, that the 

 higher cost is 

 easily offset. 



A severe test 

 not only of the 

 efficiency of the 

 tents in retaining 

 gas, but of their 

 durability, was 

 given recently at 

 Corona, Califor- 

 nia, where they 

 were used in 

 fumigating 1,000 

 newly - pruned 

 Lisbon lemon 

 trees. The tents 

 were given the 

 equivalent of two 

 years' wear and 

 tear in a few 

 days' time and 

 showed no visible 

 defects after all 

 the rough han- 

 dling, as attested 

 by members of the Growers' Cooperative Fumigating Association 

 of that place. 



STANDARD FUMIGATION METHODS POSSIBLE 

 Standardization of fumigation is the .coal for which economic 

 entomologists have long been striving, and they feel that in the 

 rubber tent their hope will at last be realized. Standardization 

 was impossible with such a variable factor as gas-leakage, possible 

 always with the porous sail-cloth and often influenced by weather 

 conditions. To hold a definite amount of gas for a definite period 

 is the very basis of fumigation, and these two essentials are quite 

 obtained, it is said, by Professor Quayl--, in the use of gas-tight 

 tenting material. Exact d<-sage, not merely to get results but 

 also to insure the tree's safety from injury by excess gas, or 

 overexposure, as has so often happened, can now be achieved. 

 Moreover, it is claimed, with gas-tight tents the dosage for small 

 trees may be reduced two-thirds; of average sized trees, one-half; 

 and very large trees, one quarter. In addition, the time of ex- 

 posure may be reduced from about an hour to an average of thirty 

 minutes. 



It is necessary, too, for trees to be kept dry during fumigation. 

 Plain canvas tents often allowed dampness to reach the fruit and 

 foliage, and when the dry gas (liquified hydrocyanic acid) unites 

 with the moisture, serious damage may be done to the tree. 

 I'nder a rubber tent the tree may be entirely safeguarded from 

 dampness as well as wind, which also interferes to some extent 



