Abstract
Prohexadione-Ca (Apogee®) was tested as a growth retardant and fire-blight control agent in the pear (Pyrus communis L. cv. Abbé Fétel) on both bearing trees in the orchard and on 1-year-old scions under greenhouse conditions. Four sprays of 50 and 100 mg·L-1 of the chemical were applied to trees in the orchard at 2-week intervals starting at petal fall, when terminal growth was 4 cm (mid-April). Scions received a single application (250 mg·L-1) and were transferred 2 weeks later to a greenhouse where the shoots were inoculated with a local, virulent strain of Erwinia amylovora (Burrill) Winslow et al. In the orchard, the higher prohexadione-Ca concentration was more effective in reducing shoot growth, enhancing fruit weight and controlling fire blight incidence and severity. Similar effects on growth parameters and disease progression were observed under greenhouse conditions. Chemical name used: calcium 3-oxido-4-propionyl-5-oxo-3-cyclohexene carboxylate (prohexadione-Ca).