Effects of Directed Applications of Prohexadione-Calcium to Tops of Mature Pear Trees on Shoot Growth, Light Penetration, Pruning and Fruit Quality

Abstract

Low-volume application of prohexadione-calcium (P-Ca, Apogee® BASF Corp.) to tops of mature pear trees reduced the vigor of shoot growth in relation to time of application, number of applications and amount of P-Ca applied. However, a second, late-summer flush of elongation of treated shoots occurred in most P-Ca treatments. Untreated trees did not produce a second growth flush. If shoot elongation in the tops of treated 'Bartlett' pear trees was reduced more than 60%, the time required for dormant pruning entire trees was also reduced. Time to summer prune 'd' Anjou' trees was reduced by treatment with P-Ca. In two of the three trials reported here, the weight of prunings removed from whole trees was reduced in proportion to the amount of P-Ca applied to the top halves of the canopies only. P-Ca treatment improved light penetration into the lower portion of the canopy in mature 'd' Anjou' pear trees whose canopies nearly touched in the row. 'Bartlett' fruit size was decreased when high concentrations of P-Ca were applied during the cell-division phase of fruit development. P-Ca produced few changes in 'Bartlett' pear fruit quality characteristics at harvest, all of which disappeared after two months of air storage. Chemical names used: calcium 3-oxido-4-propionyl-5-oxo-3-cyclohexene carboxylate (prohexadione-Ca); polyoxyethylenepolypropoxypropanol, dihydroxypropane, 2-butoxyethanol (Regulaid®).