HYBE'X'YAXIC-ACID GAS FUMIGATION IX CALIFORNIA. 



the red scale in orchards and vet these have become remfested within 

 a year. In one orchard the reinfestation was traced to some fig trees 

 on one side which had not been frunigated: in another, the scale 

 spread from a neighboring orchard across the way: while in a third, 

 the scale came from nightshade {Solatium sp.) which had not been 

 destroyed. The insect is distributed by the wind, by birds, and 

 especially by clinging to the bodies of the hordes of insects which 

 frequent citrus trees and carry them to other trees. Foremost among 

 these insects are the ladybirds (.Coccinellida? ), of which there are 

 numerous species as well as vast quantities of individuals. Before 

 fumigating for the red scale care should be taken that host weeds 

 along irrigation flumes, ditches, and fences are destroyed so far 

 as possible and all neighboring trees subject to its attacks cleaned up. 



Dosage. — The first orchard treated for the red scale '^December. 

 7 was a severely infested one of between 2 and 3 acres of trees 

 in an unhealthy condition, and was located at Sierra Madre. The 

 height of the trees was about 10 to 14 feet. The 1-1-3 formula 

 was used. Exposure lasted one hour. Dosages of from one-half 

 to 3 ounces per 100 cubic feet were used. Eradication took place 

 with aU strengths. 



In September. 190S. about 1 acre of trees about 10 feet tall, 

 located at \Vhittier. was treated with dosages of from of 1 to 1J ounces 

 per 100 cubic feet. Exposure lasted one hour. Eradication resulted. 



During April. 1909. 4 to 5 acres of iinhealthy orange and lemon 

 trees at Villa Park. Oranse Count v. were fumieated with dosages of 

 from one-half to lh of schedule No. 1. The exposures lasted 45 

 minutes, 1 hour, and 1^ hours. Complete eradication occurred. 



An acre of entirely healthy orange trees severely infested with the 

 red scale — fruit as well as leaves and branches — was treated during 

 September, 1909. The results of this experiment showed that a 

 one-half schedule usually would destroy the scale on the leaves and 

 branches, but that it required a three-fourths schedule to accomplish 

 this on the fruit. As satisfactory work was done with an exposure 

 of 45 minutes as with 1 hour. 



The examination of much work carried on by practical outfits using 

 both a three-fourths schedule and a Xo. 1 schedule has demonstrated 

 that eradication would result when careful work was done. 



Results from these extensive observations show that the red scale 

 is more easily destroyed on unhealthy than on healthy trees, and 

 that it is slightly more difficult to destroy on the fruit than on the 

 leaves and branches. The dosage used must be based on a strength 

 sufficient to destroy the scale on all parts of all trees: thus it is 

 apparent that a three-fourths schedule is the most economical for 

 the red scale. In all fumigation work against this insect it is advised 

 that a three-fourths schedule (three-fourths of schedule No. 1 (see 

 fig. 11 be used. An exposure of 45 minutes is sufficient. 



