DISEASES OF CITRUS TREES ] 91 



way to our groves. In its first stages of growth the 

 white fly looks like a very small whitish round scale, 

 thickly disseminated on the undersurface of the leaf. 

 Both sexes emerge to a winged life, in their final 

 stage, and are then a very small gnat-like insect, 

 with four milky white wings. When in its scale-like 

 stage it sucks the sap of the leaf, and checks the 

 growth of the plant or tree, being therefore directly 

 injurious, and also exudes much honey dew in the 

 same way as a scale insect, and upon this honey 

 dew the sooty fungus develops in autumn and winter. 

 The white fly requires the same treatment as the scale 

 insects. 



Phytoptus oleivorus Ashmead, the rust mite of the 

 orange is common on the orange in Florida. This 

 mite is present on both the leaves and the fruit. Its 

 presence on the leaves is often overlooked, but on the 

 fruit it extracts part of the essential oils and causes 

 a hardening or suberification of the peel, which becomes 

 paler in colour and often somewhat rusty. Oranges 

 thus affected are said to stand shipment better, owing 

 to the toughened peel, and are also said to be more 

 juicy and to acquire a better flavour. This mite attacks 

 also the lemon, and is then called silver mite of the 

 lemon. The green lemons become partly white, or 

 greenish white, a particularity shared also by green 

 oranges when attacked by the same insect. However, 

 in the case of the lemon the peel becomes useless for 

 the purpose of extracting the essential oil. Dusting 

 with flowers of sulphur on a dewy morning, or spraying 

 with sulphur mixed with ash-lye has been found a good 

 remedy against this disease, provided that the spraying 

 or dusting is repeated several times, at intervals of 

 10 to 15 days, to kill the young as they hatch. This mite 

 as well as the six-spotted mite ( Telranychus sexmaculatus 

 Riley), have originated in North America, and so far 

 do not exist in our groves. 



