226 Prohexadione-Ca: Growth Regulation and Reduction of Fire Blight Incidence in Pears, cv. `Abate Fetel'

Abstract

As in other countries, pear production in Italy requires an efficient control of excessive shoot growth. Chlormequat chloride, the only available plant growth regulator, does not necessarily represent the ideal solution because it requires high dosages, thus posing the risk of residues in fruit. Fire blight, which has invaded Italy in at the beginning of 1990, is of great concern because `Abate Fetel', one of the predominant cultivars, is highly susceptible and no preparations for control are currently available. To evaluate solutions for both aspects, prohexadione-Ca (BAS 125 11 W) has been tested on pears under growth chamber and orchard conditions. In each case, reductions of shoot growth and, if present, lowered incidences of fire blight could be achieved. Six-year-old trees of `Abate Fetel', located in an area with high fire-blight infestation pressure, were sprayed with prohexadione-Ca four times each at either 50 or 100 ppm of active ingredient at a new shoot length of 6, 12, 33, and 45 cm. The resulting final shoot length was 96% and 75%, respectively, of the control, whereas an average of 15 fire blight incidences could be found in the controls. This number was reduced to 8 and 4, respectively, in the treated trees. Fruit yield and quality was not affected.