|NORELLI, JOHN (JAY)|
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: March 6, 2004
Publication Date: June 1, 2004
Citation: Norelli, J.L., Miller, S.S. 2004. Controlling fire blight in young apple trees with prohexadione-calcium. Meeting Abstract. Phytopathology 94:576-577. 2004 Technical Abstract: Prohexadione-calcium (Apogee) (Phd-Ca) is a plant growth regulator that suppresses shoot growth in apple. In mature orchards Phd-Ca is effective in managing fire blight caused by Erwinia amylovora. However, in young apple orchards there is a need to both control fire blight and allow sufficient tree growth for tree establishment, and the utility of Phd-Ca in young orchards was unclear. When Phd-Ca was applied to orchard-grown apple trees ranging in age from newly planted to fifth season of growth (4-year-old orchards) it was found that two applications of 125 mg liter -1 Phd-Ca provided a better balance between fire blight control and growth in young orchards than three or more applications of 63 or 30 mg liter -1. Although the high rate of Phd-Ca suppressed early season shoot growth more than the lower rates, trees that received the high rate of Phd-Ca tended to grow more in the latter part of the season resulting in little or no difference in total seasonal growth between trees that received two high or three low rate applications of Phd-Ca. Fire blight control with Phd-Ca required shoot growth suppression early in the growing season and 125 mg liter -1 Phd-Ca often provided significantly better fire blight control than treatment at lower rates. Poor fire blight control occurred when the rate of Phd-Ca was lowered sufficiently to allow greater early season growth. The results indicate that one-to-two Phd-Ca applications at 125 mg liter -1 can be used to manage fire blight in the fourth to sixth season of growth when there is a high risk of shoot blight.