Prohexadione-Ca and ethephon suppress shoot growth of sweet cherry [Prunus avium (L.) L.]

A 3-yr orchard study was conducted on Tehranivee, an advanced selection of sweet cherry [Prunus avium (L.) L.] on Mazzard and Gisela 6 rootstocks, to determine the efficacy of different prohexadione-calcium (P-Ca) and ethephon (ETH) treatments on vegetative growth. In experiment 1, cherry trees were treated with 123 or 246 mg L-1 P-Ca, which was sprayed on 16 and 30 d after full bloom (DAFB) or 16, 30, and 44 DAFB. In experiments 2 and 3, trees were treated before (-6 DAFB) and after (7 and 24 DAFB) bloom with P-Ca and rates similar to experiment 1, as well as with tank-mixed sprays of 123-246 mg L-1 P-Ca and 175 mg L-1 ETH applied at various timings. P-Ca alone or in combination with ETH decreased the vegetative shoot growth by up to 74% compared with the untreated control, but this varied by cultivar and year, as well as by plant growth regulator application rate, frequency, and timing. Lower rates of P-Ca at 123 mg L-1 were as effective as 246 mg L-1. No benefit was observed in applying P-Ca before bloom before active shoot growth had begun.