NATURAL CONTROL OF WHITE FLIES IX FF.ORIDA. 09 



THE DISADVANTAGES ACCRUING TO CITRIS TREES THROIGH THE 

 USE OF PARASITIC I TNGI. 



DIRECT INJIIJY TO I'()I,IAC;E. 



Dr. 11. J. Webber gave the subject of direct injiiiy to foliage 

 some consideration in connection witli the brown fungus and re])orted 

 as follows : ^ 



Old leaves on which the larvae have been dead for some time, and on which the 

 fungus has been exposed for an extended period to the action of rain, etc., clearly 

 show the slight damage to the loaf caused ])y this fungus. Leaves which were observed 

 in March, 189G, to be badly infested with the fungus were found in December of the 

 same year to show only the remains of the pustules, the hyi)o(hallus having l>een 

 entirely washed away. That the fvmgus does some damage to the tree can not be 

 denied, buC this is clearly a secondary effect. 



The secondary injury referred to by Dr. Webber has l)een noted 

 by the authors. It may be considered as of sliglit importance. A 

 more serious secondary mjury frequently results from the prevalence 

 of the yellow Aschersonia. Dr. Webber has noted - that sooty 

 mokl frequently siuTounds and covers insects infested })y the red 

 Aschersonia. He states: 



The honeydew collected aroiuid the infected insects furnishes nourishment for 

 the sooty mold, wliich frequently springs up and makes a cons])icuous growth. The 

 growth of the sooty mold is more rapid than that of Aschersonia so that it some- 

 times happens that a rank growth of the sooty mold smothers both the insect and the 

 Aschersonia. 



The condition described is one wliicli unqtiestionably interferes 

 seriously with the respiratoiy functions of the infected leaf. Tlie 

 extent of the injury has never been estimated, so far as known to 

 the writers. Fortunately this condition is not the usual one where 

 the infection consists of the red Ascliersonia. Such a condition is, 

 however, cpiite typical when the yellow Aschersonia is abundant. 

 Moreover, the j^ellow pustules themselves, being much larger than 

 the red pustules developing on the citrus wliite fl}', cover a corre- 

 spondingly larger leaf surface. As has been indicated the secondary 

 injury residting from the yellow Ascliersonia infection is of some 

 im])ortance and withotit doubt partly offsets the benefits resulting 

 from the destruction of the wtiite-fiy larvje and pupce. 



INDIRECT INJURY THROUGH THE DISUSE OP FI'NGICIDES NEEDED TO COMRAT KUNOOUS 



DISEASES. 



In Florida the control of diseases ^ of citrus b}'^ means of fungicides 

 is seriously interfered ^\'ith by the disadvantages and supposed 

 disadvantages of the destruction of fungous parasites of destructive 



1 Bill. 1.3, Div. Veg. Phys. and Path., U. S. Dept. Agr., p. 29, 1S97. 



2 Ibid., p. 2.3. 



3 The principal diseases preventable or partly controllable by means of applications of fungicides are 

 known as melanose, die back, anthracnose, scab or verrucosis, withertii>, and scaly.bark. For the treat- 

 ment of these diseases publications of the Bureau of Plant Industry of this departniciit iind of the 

 Florida Agricultural Experiment Station should be consulted. 



