CONDITIONS FAVORABLE OK NECESSARY. 11 



deposited by these adults may have time to hatch. It is impractica- 

 ble to attempt to destroy the egg stage by fumigation, or as a rule by 

 any other direct means. The scale-like stages, however, teclmically 

 known as the larval and pupal stages, are readily destroyed when the 

 dosage is properly estimated. In Florida the month of January is, 

 everything considered, the most favorable month for fumigating for 

 the white fly. Ordinarily it would probably be undesirable to continue 

 fumigation after the adults begin to emerge in considerable numbers 

 in the spring. Tliis time of emergence, of course, varies according to 

 the locality and to weather conditions, but in general is between the 

 middle of February and the first of March. It remains for further 

 experiments to show how far fumigation may be practiced with profit 

 at other seasons of the year. It is certain, however, that in cases of 

 emergency, such as the checking of the spread of the fiy in newly 

 infested groves, fumigation can frequently be used to great advantage 

 even in midsummer. 



METEOROLOGICAL ELEMENTS. 



Light. — Fumigation is conductetl in the absence of bright sunlight, 

 to avoid injury to the foliage wliich may occur when this precaution is 

 not observed. With tents treated with oil to make them nearly gas- 

 tight, damage is almost certain to result from daylight fumigation. 

 With untreated tents, however, the writer has on several occasions 

 conducted fumigation experiments with the sun fifteen minutes high 

 ^vithout appreciable injury to the foliage. One orange tree was 

 fumigated forty minutes, beginning at 3 p. m., with the sun sliining, 

 without any shedding or burning of foliage resulting from the treat- 

 ment. The tent was placed over the tree twenty-five minutes before 

 generating the gas, and at the beginning of the forty-minute period 

 the temperature was 79.5° F., or 4.5° higher than the outside tempera- 

 ture." Twenty and one-half ounces of potassium cyanid were used, 

 and 97.7 per cent of the wliite fly pupse were destroyed. This amount 

 of cyanid was 4^ ounces less than the amount called for by the 

 table given in the Appendix. At the time of fumigation, the foliage 

 on the tree was very much curled by drought and after a few rains 

 became normal in appearance without the shedding of a single leaf. 

 The leaves, at the time of the treatment, when torn seemed to be as 

 dry as paper, although many pupse of the white fly on neighboring 

 trees in a similar condition produced adults, as did the nine speci- 

 mens which were known to survive on the fumigated tree. It is 

 probable that future experience will show that trees whose foliage is 

 curled as a result of drought are not nearly so liable to injury by 

 daylight fumigation as are trees whose foliage is in perfect condition. 



Fumigation can safely begin with sundown, or, during the fumigat- 

 ing season in Florida, between 4 and 5 o'clock p. m. On dark, cloudy 

 days fumigation seems entirely safe at any time with untreated tents. 



