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Title: Severity of scab and its effects on fruit weight in mechanically hedge-pruned and topped pecan trees

Author
item Bock, Clive
item Hotchkiss, Michael - Mike
item BRENNEMAN, TIM - University Of Georgia
item STEVENSON, KATHERINE - University Of Georgia
item GOFF, WILLIAM - Auburn University
item SMITH, MIKE - Oklahoma State University
item WELLS, LENNY - University Of Georgia
item Wood, Bruce

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/12/2016
Publication Date: 2/16/2017
Citation: Bock, C.H., Hotchkiss, M.W., Brenneman, T.B., Stevenson, K.L., Goff, W., Smith, M.W., Wells, L., Wood, B.W. 2017. Severity of scab and its effects on fruit weight in mechanically hedge-pruned and topped pecan trees. Plant Disease. doi:10.1094/PDIS-10-16-1473-RE.

Interpretive Summary: Scab is the most damaging disease of pecan in the southeastern USA. Pecan trees can attain 44 m in height, so managing disease in the upper canopy is a problem. Fungicide is ordinarily applied using ground-based air-blast sprayers. Mechanical hedge-pruning and topping of pecan may improve management of scab in the humid, wet Southeast. Disease was monitored in hedge-pruned and non-pruned trees to compare control efficacy under the same fungicide regimes. Results showed that hedge-pruning did not result in more severe scab. But sample height in the canopy invariably had a large and significant effect; with more sever scab at greater heights. In trees >~12.5 m tall, hedge pruning allowed more efficacious control of the disease as the whole canopy was within reach of fungicide sprays. Fruit weight depended on sample height, with fruit most often weighing less when collected at greater sample heights as they had less protection from fungicides. Hedge-pruning and topping pecan tree canopies to manage tree size and will enable better fungicide coverage, reducing risk of a scab epidemic as more of the canopy is assured efficacious fungicide spray coverage.

Technical Abstract: Scab is the most damaging disease of pecan in the southeastern USA. Pecan trees can attain 44 m in height, so managing disease in the upper canopy is a problem. Fungicide is ordinarily applied using ground-based air-blast sprayers. Although mechanical hedge-pruning and topping of pecan is done for several reasons, improved management of scab is an important reason in the humid, wet Southeast. Resulting shoot growth on cut limbs of susceptible cultivars could lead to more severe scab. In three experiments over three years, we explored the effect of hedge-pruning trees to ~12-14 m compared to non-hedge-pruned trees. All trees received fungicide treatments (air-blast sprays =3 aerial applications). Hedge-pruning either had no effect, or increased or decreased scab severity only slightly on leaflets, immature or mature fruit (a -9.95 to +14.63% difference in scab severity compared to the control). However, height in the canopy invariably had a large and significant effect on scab severity, and amounted to a 0.05 to 73.77% difference in severity between the lowest and highest sample in the canopy. Fruit weight depended on sample height, with fruit most often weighing less when collected at greater sample heights. A robust relationships between fruit weight and scab severity was found at the highest sample heights where scab was also most often severe (R2 = 0.21 to 0.67, P<0.0001). Hedge-pruning and topping pecan tree canopies to manage tree size will enable better fungicide coverage, reducing risk of a scab epidemic as more of the canopy is assured efficacious fungicide spray coverage.