Three experiments were conducted on 'Empire' apple (Malus xdomestica Borkh.) to evaluate the effects of hard water, calcium chloride (CaCl 2), water conditioners, surfactants, and captan fungicide on the growth reduction and fruit cracking caused by prohexadione-calcium (PC). Two applications of 63 mg·L-1 PC provided season-long growth control in two studies. Adding a water conditioner to PC reduced shoot growth more than an application of PC in hard or soft water in one New York study. Ammonium sulfate (AMS) and Choice were equally effective water conditioners. PC provided no growth control of water sprouts and had no effect on fruit set or yield. PC applied at 250 mg·L-1 reduced fruit size. 'Empire' fruit cracking and corking was severe, despite the use of only 63 mg·L-1 PC in two of the three experiments. This damage was exacerbated by the addition of a water conditioner, however AMS applied with a surfactant but without PC had little or no effect on either the severity or extent of fruit injury. In a third experiment, the addition of surfactants, CaCl2, or captan to 250 mg·L-1 PC plus a water conditioner had no effect on the severity of fruit damage. Fruit cracking caused by PC increased preharvest drop in two of three experiments, and increased postharvest rot in the Geneva, N.Y., experiment where fruit were stored prior to grading. Application of PC plus a water conditioner reduced estimated gross return per hectare for 'Empire'. We conclude that the fruit injury is caused by the formulated PC product itself under certain environmental conditions, and that this product should not be used on 'Empire'. Chemical name used: calcium 3-oxido-4-proprionyl-5-oxo-3-cyclohexine- carboxylate [prohexadione-calcium (PC)].
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