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ARS Home » Southeast Area » Poplarville, Mississippi » Southern Horticultural Research » Research » Publications at this Location » Publication #354953

Research Project: Production and Disease and Pest Management of Horticultural Crops

Location: Southern Horticultural Research

Title: Effect of Phosphorous Acid and Pruning Height on Renovated ‘Woodard’ Rabbiteye Blueberry

Author
item STAFNE, ERIC - Mississippi State University
item Smith, Barbara

Submitted to: Blueberry Research Extension North American Workers Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 8/12/2018
Publication Date: 10/15/2018
Citation: Stafne, E.T., Smith, B.J. 2018. Effect of Phosphorous Acid and Pruning Height on Renovated ‘Woodard’ Rabbiteye Blueberry. Blueberry Research Extension North American Workers Conference Proceedings. pg.16. https://digitalcommons.library.umaine.edu/nabrew2018/proceedingpapers/proceedingpapers/16.

Interpretive Summary: Pruning is often recommended as the best way to renovate older rabbiteye blueberry plants, but it is stressful on the plants and results in a lost year of fruit production; however, if recovery stress could be reduced, perhaps a quicker return to fruiting could occur. One possible way to reduce this stress is application of phosphorous acid that may act as a biostimulant as well as a fungicide. The purpose of this study was to determine if the application of phosphorous acid would have a beneficial effect on blueberry plant growth and yield when combined with pruning at two different height levels. Pruning blueberry bushes to a height of 50 cm increased yield and fruit weight significantly compared to bushes pruned to ground level and resulted in more shoots and hastened harvest. The application of phosphorous acid showed no benefit, whether applied as a drench or foliar, after one season; but more time is needed to ascertain any differences as it has an induced, rather than direct effect. This information is important to blueberry growers, farm advisors, and extension personnel making orchard management decisions. This should result in a more plentiful supply of affordable, nutritious blueberries for the American consumer.

Technical Abstract: Phosphorous acid is a fungicide that may have other plant health-inducing properties. A previous study showed greater vigor in blueberry plants treated with phosphorous acid. In the current study, old, low-vigor ‘Woodard’ rabbiteye blueberries were selected for renovation in 2017. The bushes had not been pruned or otherwise managed in several years. To test the hypothesis that adding phosphorous acid treatments (Agri-Fos) to the renovation process would increase plant vigor, three treatments were used: no addition of phosphorous acid, phosphorous acid applied as a drench at renovation pruning, and monthly foliar applications of phosphorous acid after renovation pruning and the following year. Two pruning height treatments were also done on July 14: bushes were pruned at ground level and bushes pruned at 50 cm. End of season shoot number was significantly different between the 50 cm cut and the ground level cut treatments (35.6 shoots/bush vs. 21.3 shoots/bush, respectively). However, shoot length was greater for the ground cut (80.5 cm) vs. 50 cm cut (72.1 cm). Shoot diameters were not significantly different. Other factors such as first bud push after pruning and crop load rating were not significant. Yields were higher for the 50 cm cut treatment when compared to the ground level prune (318.7 g vs. 58.1 g, respectively). Interestingly, phenological development recordings of flower stage did not differ at stages 2 to 4 but were different in stages 5 and 6. Flower development on bushes in the 50 cm cut treatment was earlier by nine days at stage 5, nine days at stage 6, and five days at stage 7 compared to those in the ground cut treatment. There were no significant differences due to phosphorous acid treatments in any data evaluated, nor any significant interactions between phosphorous acid treatment and pruning height treatment. More time may be needed to ascertain any differences among phosphorous acid treatments as it’s effect is induced rather than direct.