FRANK E. GARDNER 211 



susceptibility, as in the case of apples. A great deal more work needs to 

 be done under Florida conditions and with Florida varieties to establish 

 the most effective safe concentrations and times for application. In the 

 Florida drop control experiments the sprays have thus far been applied 

 in the late fall months not only because this is near the beginning of the 

 drop period, but also because the trees are not flushing new growth and 

 do not normally do so until February and can therefore withstand a 

 higher concentration without injury than at other periods. Moreover, 

 sulphur sprays and dusts for rust mite control are commonly applied 

 at this time, and it appears entirely feasible to include 2,4-D at no 

 extra expense other than its insignificant cost. The results thus far 

 indicate, however, that the presence of wettable sulphur moderately 

 reduces the effectiveness of the 2,4-D, although it is possible that this 

 difficulty may be overcome simply by increasing the amount used. The 

 low cost of this material and the possibihty of including it in pest-control 

 sprays are important assets favoring its wide adoption for citrus fruits. 

 Pears. — Passing reference has already been made to the drop of pears, 

 but since this fruit responds to hormone sprays so readily, it appears 

 desirable to review briefly the present status of its drop control. Summer 

 pears for the fresh fruit market are harvested prior to full maturity, 

 and thus a drop problem is usually not of great moment. Canners, on 

 the other hand, need to have the fruit more nearly ripe, and the delay 

 in picking for this purpose and for increased size results in appreciable 

 amounts of grounded fruit. Apparently Strickland ei al. (47) in Aus- 

 tralia were the first to report pear drop control by hormone sprays. 

 Their treatments with 20 ppm. of naphthaleneacetamide in three appli- 

 cations have since been shown to be much more extravagant than 

 necessary. Davey and Hesse (12) obtained appreciable control in Bartlett 

 variety witn both NAA and its amide at 5 and 10 ppm. They make no 

 mention of injury from NAA at the higher concentration, although 

 Batjer et al. (6) reported a yellowing and premature drop of considerable 

 foHage from this concentration. These last investigators obtained effec- 

 tive drop control of Bartletts with 2.5 ppm. of either NAA or 2,4-D. 

 Concentrations of 2,4-D higher than 2.5 ppm. (5 and 10 ppm.) caused 

 yellowing of old foliage, injury to buds, and malformation of new fruit 

 and foUage in the following season proportional to the increase in 

 concentration. Overholser et al. (35) mentioned that Bosc variety, as 

 well as Bartlett, responds to NAA; but these workers did not try 2,4-D. 



