64 FUMIGATION FOR THE CITRUS WHITE FLY. 



favors the eflfectiveness of fungous and bacterial diseases, all give 

 basis for the hope that complete control by natural enemies will be 

 the eventual conclusion of the white-fly problem. A thoroughly 

 scientific and practical investigation, however, can not lead to lasting 

 benefits if the conclusions Tepresent merely desired results and are 

 unsupported by sufficient evidence and experience. Wliile a great 

 deal has been learned concerning the fungous diseases of the white 

 fly, the present investigations of this Bureau have not thus far shown 

 that any method can be relied upon to materially assist nature in 

 controlling the pest to the point of preventing all or nearly all of its 

 injury. The dissemination of these diseases is readily accomplished 

 under certain favorable conditions, but how far artificial dissemina- 

 tion, at its best, with our present methods goes toward the successful 

 control of the white fly is still problematical. 



Manatee County is the only large orange-growing district where the 

 fungous diseases have proved of much assistance. Data obtained 

 from many orange growers and personal observation by the writer 

 and other entomologists connected with the Bureau of Ento- 

 mology indicate that the fimgi, without artifical aid, reduce the 

 injury from the white fly about one-third. Undoubtedly without the 

 aid of these fungous friends the damage in Manatee County would 

 average more than 50 per cent. With this as a minimum estimate, 

 the average damage in Manatee County, allowing a benefit of one- 

 third from the fungi, amounts to 34 per cent. One year in three, it is 

 the experience of the growers in this county, the fungi have so 

 thoroughly cleaned up the pest that the fruit is clean and requires no 

 washing. The f<illowing year the insects are in the ascendency and 

 the fruit and foliage become blackened with sooty mold to as great 

 an extent as can be observed anywhere in the State. This is due to the 

 fact that the fungi liave diminished the white flies the previous year to a 

 point where they cease to flourish. Late in the second year, however, 

 with the fly abvmdant, the fungous enemies develop rapidly. The third 

 year the effect of the l)lackening of the foliage is apparent in a greatly 

 reduced crop, while during this year the fly is again reduced to a negligi- 

 ble c^uantity, permitting a good crop of fruit to set and remain clean 

 from sooty mold during tlie followang season. The above is the usual 

 course followed in individual groves. Considering the county as a 

 whole in 1906, fully three-fourths of the groves were so free from sooty 

 mold as to require no washing of the fruit. It was generally con- 

 sidered that this condition had never before been equaled since the 

 wlrite fly first obtained a foothold in this county. In one case, how- 

 ever, it was claimed by one of the leading orange growers that an 

 isolated grove had become practically clean through some unkno^\^l 

 agency, the prevailing fungous diseases not being present in sufficient 

 al)undance to accomplish any noticea])le result. Nevertheless, the 

 fungous enemies referred to were undoubtedly of prime importance 



