BULLETIN 645, U. S. DEPARTMENT OF AGRICULTURE. 



parasitic on certain injurious insects, excellent as they are, have 

 fallen short of what was expected, of them, but more as a result of a 

 spraying system developed by the writer, which, by taking all pests 

 into consideration instead of merely the white flies, has proved the 

 direct financial gain that will follow the intelligent application of 

 spray mixtures. It is to certain advantages of this system of spray- 

 ing that attention is called in this bulletin. Perhaps the best argu- 

 ment in favor of spraying is to be found in the difficulty experienced 

 in securing the same grove for demonstration purposes two or three 

 years in succession. Once the owner has seen with his own eyes the 

 benefits resulting from careful and well-timed spraying, he refuses 

 to accept the losses that he knows will come to him or his company 

 through the setting aside of blocks of trees to serve as checks in com- 

 munity demonstration work. 



PESTS OF IMPORTANCE. 



Of the total damage caused by insects and mites to citrus in 

 Florida, more than 95 per cent may be attributed to six species. In 

 the order of their destructiveness, these are the citrus white fly, 1 the 

 purple scale, 2 the rust mite, 3 the red scale, 4 the cloudy- winged white 

 fly, 5 and the red spider. 6 There are several other pests of secondary 

 importance, such as the woolly white fly, 7 the purple mite, 8 and the 

 chaff scale. 9 The citrus white fly now infests nearly all the groves 

 in the State. The purple scale is found in greater or less numbers on 

 every citrus tree. 



INJURY TO TREES AND FRUIT. 



The presence of these pests on the trees and fruit produces 

 blemishes which cause fruit to be placed in a much lower grade than 

 would be the case if these blemishes were not present. While the 

 excellent methods of washing the fruit remove nearly all the sooty 

 mold which follows attacks of the white fly, usually some of it is left 

 near the stem end. When this is present the fruit is placed in a grade 

 lower than if it were absent. The presence of scale insects on the fruit 

 lowers the grade, and, when these are abundant, makes the fruit 

 practically unmarketable unless the scales are removed by hand wash- 

 ing. Perhaps the greatest cause for lowering the grade of fruit is 

 the blemish following rust-mite injury. All these pests devitalize the 

 trees, and this type of injury is much more important than the low- 

 ering of the grade of the fruit, because the yield is reduced. This 



1 Dialeurodes citri Ashmead. 



2 Lepidosaphes beckii Newman. 



3 Eriopliyes oleivonis Ashmead. 



4 ChrysompJidlus aonidum Linnaeus. 



■■ Aleyrodes nubifera Berger, now known 

 as Diaieurodes citrifolii Morgan. 



6 Tetranychus sextnaculatus Riley. 



7 Aleurothriatus howwrdi Quaintance. 



8 Tetranychus citri McGregor. 



9 Parlatoria pergandii Comstock 



