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Poster: Biology & Disease Mgmt: Cultural Control


Scab severity in relation to hedge pruning pecan trees in the Southeastern USA
C. BOCK (1), M. Hotchkiss (1), T. Brenneman (2), K. Stevenson (2), B. Goff (3), M. Smith (4), L. Wells (5), B. Wood (1) (1) USDA-ARS SE Fruit & Tree Nut Research Laboratory, U.S.A.; (2) Department of Plant Pathology, University of Georgia, U.S.A.; (3) Dep

Scab is the most damaging disease of pecan in the Southeastern USA. Pecan trees are tall (up to 30+ m), and managing disease in the upper canopy is problematic. Hedge pruning trees to ~12 m is being explored to facilitate efficacy of ground-based fungicide sprays, but resulting vigorous shoot growth could result in more severe scab. Nine experiment compared scab severity on trees receiving hedge pruning regimes vs no hedging. All trees received fungicide treatments (ground-based air-blast sprays and up to 3 aerial applications). Results showed that different hedging methods either had no effect, increased or decreased scab severity on immature fruit in one experiment (P<0.0001, assessed before mid-August [immature fruit were assesses in 8 of the 9 experiments]), and on mature fruit in 6 of 9 experiments (P<0.0001, assessed after mid-August), but in all cases differences were small. However, height in the canopy invariably had a significant effect on scab severity, with up to 18-fold more severe scab on fruit at ≥12 m compared to 5 m. Immature fruit high in the canopy had more severe scab in all experiments (P<0.0001-0.03), and mature fruit had more severe scab in 6 of 9 experiments (P<0.0001). In trees that received the same fungicide program the effect of hedging in increasing scab severity was negligible and not consistent, but scab was consistently more severe at greater heights in the canopy of both hedge pruned and non-hedged trees.