14 BULLETIN 1117, U. S. DEPARTMENT OF AGRICULTURE. 



reasonable and fairly accurate check on the activities of the fungus 

 in the field. The table shows that of the first collection on June 13 

 only 11 per cent died of the disease, whereas in the last collection 94 

 per cent succumbed ; and, furthermore, that the percentage of mortal- 

 ity jumped from 18 on June 22 to 64 on June 29, an increase of 46 

 per cent in one week's time. The rapidity with which such diseases 

 spread when once established is remarkable, and it is strange that 

 any insects escape alive. 



Figure 1 records the events that occurred in one grapefruit grove. 

 It is reasonable to believe, owing to the wide distribution of the 

 fungus, that similar epidemics were present elsewhere, and that as 

 a matter of fact such widespread destruction of the mealybug has 

 been going on for years, unobserved and therefore unheeded by the 

 citrus growers of the State. 



RELATION OF FUNGICIDES TO MEALYBUGS. 



From the standpoint of the citrus grower, which in fact is the 

 true position for others who make recommendations to assume, 

 insect and fungous enemies are lumped together in one category as 

 injurious factors — factors which among other things tend to inhibit 

 the health and growth of the trees and lower the marketability of 

 the fruit. It is of no concern to the grower whether injury is 

 caused by insects or diseases, except in so far as it is necessary for him 

 to know the differences in order judiciously to apply remedial 

 measures. He sees only the damage caused and translates it into 

 dollars and cents. Unconsciously, perhaps, he mentally segregates 

 these enemies — whether correctly or not is beside the point — into 

 classes, according to the amount of damage or injury they have 

 caused in the past when no artificial measures have been employed 

 to control them. He has formed an opinion, for example, of the rela- 

 tive injury wrought by rust mites, white flies, melanose, scab, the 

 purple scale, etc., and although this opinion may be erroneous, it 

 will influence him in applying control measures. Although most 

 growers would like to control all of their insect and fungous enemies, 

 few attempt to do so. The majority are forced, for what they regard 

 as economic reasons, to control the most injurious. If certain dis- 

 eases seem to be causing great losses their control will be sought first, 

 or if insect pests are particularly prevalent, these will first be the 

 subject of control measures. In other words, if in the grower's opin- 

 ion all of the citrus enemies can not be controlled economically, only 

 those will be chosen for control that are causing the most injury. 

 Such a procedure is natural and logical, as the object striven for is 

 economic gain. 



The artificial control of citrus diseases in Florida by fungicides 

 and the natural control of injurious citrus insects by entomogenous 



