482 INJURIOUS AND BENEFICIAL INSECTS OP CALIFORNIA. 



FOR ANTS' AND WASPS' NESTS 



A small amount of carbon bisulfid poured into the underground 

 nests of ants, wasps, yellow jackets and other insects of like habits 

 will usually exterminate the colony. This method, however, is of 

 little avail against the Argentine ant, because of the many small 

 nests. 



TOBACCO FUMES 



For very tender house and greenhouse plants infested with plant 

 lice, thrips and other small insects or mites, it is sometimes advisable 

 to fumigate them with slowly burning tobacco, to avoid injury to the 

 foliage, but even in such cases hydrocyanic acid gas, if properly 

 handled, is much better and is gradually replacing the tobacco punk 

 and other commercial fumigants of a similar nature. 



HYDROCYANIC ACID GAS 



Hydrocyanic acid gas is usually generated by the addition of 

 cyanide to diluted sulphuric acid. The generation is made in an 

 earthenware jar, or in a special fumigating machine, the gas being 

 confined in a fumigating house or, as is more often the case in Cali- 

 fornia, in a tent thrown over a tree. For many years the size of 

 the dose to be given depended entirely upon the guess of each 

 fumigator, there being no uniform practice in this respect. The 

 results of this early guesswork so clearly showed the need of systema- 

 tism that the State University and the United States Depart- 

 ment of Agriculture set experts to work out a more reliable and 

 uniform system of dosage. Prof. C. W. AVoodworth was the first to 

 design and use marked tents and published dosage schedules based 

 on measurements. 334 Dr. A. W. Morrill 335 designed the style of 

 marked tents known as "the Morrill system," which is generally 

 used throughout the State. His work was done in Florida, where 

 Prof. C. W. Woodworth first used marked tents several years pre- 

 viously in fumigating for the white fly. 330 Later R. S. Woglum 337 

 began operations for the United States Department of Agricul- 

 ture in California and carefully tested "the Morrill system" so 

 as to make its practicability and availability apparent to all of the 

 orchardists. 



TENTS 



Shape. — In order to conform as near as practicable to the form of 

 a tree, fumigation tents are made in the shape of an octagon (8-sided, 

 Fig. 482). If the tents were square the corners Avould be a constant 

 and unnecessarjr annoyance. 



For small trees, bell tents were formerly made dome-shaped with a 

 strong hoop sewed around the bottom. Such tents are seldom if 

 ever used at the present time. 



33 *Bul. No. 152, Cal. Agrcl. Exp. Sta., 1903. 



335 Bul. No. 76, Bur. Ent. U. S. Dept. Agric. 



336 Bul. No. 67, Fla. Agrcl. Exp. Sta. 



3 "Bul. Nos. 79, 90 (pts. I and II), Bur. Ent. U. S. Dept. Agric, 1909, 1911. 



