496 SUCCESSFUL FARMING 



understood. When caused by use of organic manure, such as blood, stable 

 manure and the like, it is cured by stopping fertilization and cultivation 

 for a period and mulching the tree. When caused by lack of drainage, 

 tile drainage of the area frequently results in a cure. 



Mottle leaf, a very common and injurious malady in California, is an 

 obscure disease, the cause of which is not yet known. Very extensive 

 investigations of this disease are now in progress. 



Citrus canker, a very serious malady caused by a bacterium (Pseudo- 

 monas citri), has recently become epidemic in Florida and the Gulf states. 

 It is now known to occur in Japan and the Philippine Islands and was 

 apparently introduced into Florida from one of these sources. An extensive 

 campaign is now being waged to eradicate this disease by burning all 

 infected trees. 



Verrucosis, or scab, and melanose are two important fungous diseases 

 occurring in Florida that have not appeared as yet in California. Wither- 

 tip, caused by the fungus Colletotfichum gloeosporioides, is common both in 

 California and Florida. It is controlled by pruning accompanied by spray- 

 ing with Bordeaux mixture. 



Many fruit rots caused by such fungi as the cottony mold (Sclerotinia 

 libertiniana) , brown rot (Pythiacystis citrophthora) , blue mould (Penicillium 

 italicum) and green mould {Penicillium digitatiwi), cause considerable 

 loss in the packing-house and in shipment. These are controlled by careful 

 handling, by the use of disinfectants in the wash water and the proper 

 sterilization of the fruit boxes and packing-house machinery and the like. 

 (For other diseases see Chapter 75.) 



Insects. — Insect pests are very numerous in all citrus sections and 

 require the systematic use of control methods to insure the financial success 

 of the industry. By far the most serious pests are the scale insects of which 

 there are numerous kinds. 



In California the most common scale insects are the black scale (Sais- 

 setia olece), the citricola scale (Coccus citricola), the red scale (Chrysomphalus 

 aurantii) and the purple scale (Lepidosaphes beckii). The control of these 

 scale pests is aided to some extent by various parasites, but fumigation 

 with hydrocyanic acid gas about once every two years, or more often if 

 necessary, is almost universally practiced. 



The cottony cushion scale (Icerya purchasi), which at one time was so 

 serious as almost to threaten the life of the citrus industry in California, 

 has been so thoroughly controlled by the introduction of the Australian 

 ladybird beetle that it has ceased to be considered a serious pest. 



In Florida the most common scale insects are the purple scale (Lepido- 

 saphes beckii), the long scale (Lepidosaphes gloverii), the Florida red scale 

 (Chrysomphalus aonidum), the chaff scale (Parlatoria pergandii), the soft 

 brown or turtle-back beetle (Coccus hesperidum), the black scale (Saissetia 

 olece) and the hemispherical scale (Saissetia hemisphcerica) . In the control of 

 these insects in Florida, more reliance is had upon parasitic fungi and insect 



