FUMIGATION OF CITRUS TREES. 57 



purple-scale eggs than all the rest of the tree, and on the hatching 

 of these eggs the insects will spread to other parts of the tree. The 

 danger from old scaly fruit is evident, and all such should be re- 

 moved from the trees before fumigating an orchard* 



There are times in which a scale-infested orchard to be treated 

 contains some scale on the green fruit. During the autumn season 

 when fumigation is most practiced the purple scale is largely in its 

 earlier stages of development, in which it may be destroyed by the 

 employment of schedule No. 1. The immature fruit which is scale 

 infested can be left on the tree. It is the old scaly fruit which requires 

 removal at the time of fumigation. 



TWO SUCCESSIVE TREATMENTS. 



A few growers whose groves are severely infested with the purple 

 scale will desire to have the scale eradicated if possible, even though 

 the initial expense is considerably above the cost of a regular treat- 

 ment, yet they do not care to assume the risk of having any fruit 

 on the trees injured. In such cases some authorities advise two 

 successive treatments during the early autumn and about five or six 

 weeks apart. The dosages used should be sufficient to destroy the 

 mature insects. The first treatment would destroy all the insects, 

 leaving only eggs on the trees. The time elapsing between this and 

 the second treatment should be just long enough to allow all the eggs 

 to hatch. About five weeks is supposed to be sufficient unless the 

 weather be exceptionally cool. Careful inspection will settle this 

 point. If the first treatment has been thorough and there are no eggs 

 present at the second, eradication should result. A three-fourths 

 schedule should be used in each treatment. The first fumigation 

 should be in the autumn, not later than the first part of October. 

 Double fumigation is seldom resorted to, as its economy in the long 

 run is somewhat questionable. 



THE RED SCALE. 



The red scale is generally held as the most difficult of all citrus scales 

 to destroy. Extensive experiments during this investigation, carried 

 out in many sections of southern California, have proved it to be one 

 of the easiest to destroy. It is, however, the most difficult insect to 

 keep out of an orchard when once it has become established in a com- 

 munity, and this may be the basis for the opinion as to its greater 

 resistant power to hydrocyanic-acid gas. By reason of its great pro- 

 lificness, its infestation of some weeds common about citrus orchards 

 as well as many trees and shrubs which are sometimes planted on 

 driveways or about the buildings on the premises, and the ease with 

 which it spreads, this insect frequently will quickly reinf est an orchard 

 which has been treated. Live insects left on a few trees in an orchard 

 quickly multiply and infest the others. The author has eradicated 



