FUMIGATION OF CITRUS TREES. 9 



its habit of secreting honeydew, which spreads over the leaves, fruit, 

 and branches, furnishing a growing medium for a black or sooty 

 mold fungus, resulting in a black coating throughout the tree. This 

 coating is removed from the fruit by washing, or in light attacks by 

 brushing. In the investigations by Dr. G. Harold Powell * of the 

 causes of decay of oranges while in transit from California, it was 

 shown that the decay was greater in washed than in unwashed fruit. 

 To avoid the washing of fruit it is necessary to destroy the scale 

 in the orchards. The black scale appears generally to have little 

 effect on the vitality of the tree. Its attacks are confined mainly 

 to the branches, yet it is commonly found on the leaves during its 

 earlier stages of development, and sometimes it matures in this situa- 

 tion. Seldom does it mature on the fruit. The young of the black scale 

 insects hatch from eggs deposited by the adult. They can be readily 

 destroyed by fumigation in the early stages of development. Ap- 

 proaching maturity they become tough and leathery, and in this 

 condition they are capable of resisting very heavy dosages of gas. 

 The breeding of the black scale in southern California has never been 

 closely investigated, so the exact number of broods is not known. 

 When this has been done undoubtedly it will be found to be very 

 variable with different hosts, or even on the same host. The scales 

 on " sucker" shoots will mature much more rapidly than those on 

 other parts of the tree. There is one noticeable general brood which 

 is usually largely hatched by the first part of September. In the 

 warmer and drier parts of the citrus belt, remote from the coast, the 

 hatching of this brood is quite distinct, so that in most instances all 

 the insects may be found in the early stages of development at the 

 same time. In the immediate vicinity of the coast, and especially 

 on recently budded trees, one frequently finds the scale in all stages 

 of development on the same tree. In these latter instances fumi- 

 gation will prove less satisfactory than in the former. 



THE RED SCALE. 



(Chrysomphalus aurantii Mask.) 



The red scale, although its injuries are more severe in some local- 

 ities than in others, has the limits of its distribution very much the 

 same as has the black scale. It can be found within a few miles of 

 the ocean or as far inland as Redlands. This insect occurs on many 

 host plants besides citrus trees. It attacks the fruit, leaves, and 

 branches. In point of destructiveness it excels all other citrus scale 

 insects in this State, destroying not only branches, but sometimes 

 entire trees by its attacks. The young are born alive. It has at 

 least three broods and is very prolific. 



i Bui. 123, Bur. Plant Ind., U. S. Dept. Agr., 1908. 



