54 HYDROCYANIC-ACID GAS FUMIGATION IN CALIFORNIA. 



severely infested with purple scale, was fumigated with the 1-1-3 

 formula with an exposure of one hour. Dosages varying from 1J 

 to 2 J ounces per 100 cubic feet were used. The result was that 

 eradication occurred on the leaves and branches at a rate of 2 ounces 

 per 100 cubic feet, thus corroborating the work on such small trees 

 previously carried on at Orange. 



Eradication of an insect would be preferable, yet experience during 

 these experiments just mentioned demonstrated that the dosage 

 required for eradication might result in injury to the fruit. A rate 

 of 1 ounce per 100 cubic feet for trees about 11 to 12 feet high was safe 

 under almost all conditions and such a rate was adopted for general 

 work. Dosage schedule No. 1, based on such a strength of gas, was 

 prepared at this time. 



This schedule No. 1 was used during the autumn of 1908 by several 

 practical outfits in the vicinity of Whit tier, and has since been fol- 

 lowed in other sections in which the purple scale occurs. Thousands 

 of acres have been fumigated after this schedule. The general result, 

 when the work has been carefully done, has corroborated the writer's 

 own experiments in that all live insects and in excess of 99 per cent 

 of the eggs were destrwed on the leaves and branches. Such a 

 killing is entirely satisfactory. In some cases a slight amount of 

 pitting of fruit has occurred, especially in the top of the trees, and has 

 caused some growers to complain. This slight amount of pitting can 

 be overlooked by reason of the superior killing which has resulted. 

 To use a dosage sufficient to control the scale and at the same time 

 entirely avoid pitting throughout a fumigating season is a practical 

 impossibility. 



The first season the improved system of fumigation was adopted 

 schedule No. 1 was used almost universally. As this schedule gives 

 dosages considerably in excess of those formerly used, fumigators in 

 general became somewhat uneasy about using it, with the result that 

 during the season of 1909 a three-fourths schedule, rather than full 

 schedule No. 1, was used by the majority of outfits. Although the 

 results with the three-fourths schedule have been very good, this 

 schedule is far less satisfactory than the full schedule No. 1. 



The writer advises the use of full schedule No. 1 (see fig. 9, p. 34) 

 for the purple scale. The results with this dosage are so superior, as 

 shown by experience, that most orchards are rendered so clean that 

 thereafter they do not require fumigation oftener than once in two 

 years. It is more economical to use schedule No. 1 and escape treat- 

 ment alternate years even if a little fruit is pitted in the operation 

 than to use a smaller dosage and be obliged to treat an orchard every 

 year. It is seldom, however, that any marked degree of pitting takes 

 place with schedule No. 1, if proper care is exercised during the 

 operation. 



