Abstract:
Fruit set of sweet cherries was reduced if sprays containing fluoride
(sodium or ammonium fluoride or hydrofluoric acid) were applied during
anthesis. Sprays applied at other times during the fruit-growing season caused
fruit and leaf symptoms, depending on the concentration of fluoride, but no
reductions in fruit set. Symptoms of fluoride toxicity were blackening, shriveling,
and "dimpling"; increased firmness of the stylar end of the fruit and
marginal necrosis; interveinal chlorosis, cupping, reduced leaf size, and a loss of
leaf tip. Similar responses were found, both with respect to fruit set and
symptom expression, when sweet cherry limbs were enclosed in mylar cages and
fumigated with gaseous hydrogen fluoride for varying periods of time at
varying air fluoride concentrations. Fruit set reduction was linearly related to
increasing dose of fluoride (expressed as hours exposure times concentration of
fluoride in μg/m'). Germination of pollen and growth of pollen tubes were
found to be inhibited by fluoride.
Growth of fruit and vegetative tissues was influenced only at the higher
levels of gaseous fluoride tested (4-6 )Ag/m') and generally after whole season
treatment.
