Evaluating different approaches in the application of phosphonates for the control of apple root diseases
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Phosphonate fungicides are registered on various tree crops in South Africa for the management of oomycete root rot pathogens, but not on apple trees. The study investigated several phosphonate treatments previously evaluated independently by technical advisors in South Africa. A replicated orchard trial was conducted in non-bearing asymptomatic orchards; tree roots were infected by oomycetes but foliar symptoms were absent. Phosphonate foliar-, trunk paint- and soil drench treatments were equally effective, and consistently resulted in a significant reduction in Phytophthora cactorum and Pythium irregulare root DNA quantities relative to the non-treated control. The latter was not always true for phosphonate trunk spray treatments. Trunk paint applications applied at an annual dosage of 40 g phosphorous acid/tree yielded significantly higher root phosphite (breakdown product of phosphonates) concentrations than the soil drench and trunk spray applications; the latter were applied at lower annual dosages of 7.5 g a.i./tree and 20 g a.i./tree, respectively. Foliar sprays applied at a low annual dosage (1.8 to 3.0 g a.i./tree) often outperformed the soil drench and trunk spray treatments in root phosphite concentrations. No clear association was evident between root phosphite concentrations and pathogen suppression. Root phosphite typically peaked at 8-weeks post-treatment for winter applications, and between 2- to 4-weeks for summer applications. A rapid decline in root phosphite was evident over the 12-week summer period, but not for winter applications. Monitoring root growth in the untreated control plots showed that root growth was continuous but that it peaked in summer, with reduced growth in winter.
KeywordsPhosphonates Phytophthora cactorum Pythium irregulare Apples Phosphite Phosphorous acid
We acknowledge the South African Apple and Pear Producer’s Association (SAAPPA), the Technology and Human Resources for Industry Programme (THRIP) for financially supporting the research, and without whom this research would not be possible. We are appreciative of Marieta Van der Rijst (Agricultural Research Council, Biometry Unit, Stellenbosch, South Africa) for statistical analyses of the data.
- Garbelotto M, Schmidt DJ, Harnik TY (2007) Phosphite injections and bark application of phosphite+ Pentrabark™ control sudden oak death in coast live oak. Arboricult Urban For 33:309Google Scholar
- Giblin F, Pegg K, Thomas G, Whiley A, Anderson J, Smith L (2007) Phosphonate trunk injections and bark sprays. In: Proceedings of sixth world avocado congress (Actas VI Congreso Mundial del Aguacate), pp 12–16Google Scholar
- Graham JH (2011) Phosphite for control of Phytophthora diseases in citrus: model for management of Phytophthora species on forest trees? N Z J For Sci 41:49–56Google Scholar
- Loescher WH, McCamant T, Keller JD (1990) Carbohydrate reserves, translocation, and storage in woody plant roots. HortScience 25:274–281Google Scholar
- Lötze E, Van Zyl F, Taylor N (2018) Quantifying white root growth dynamics of bearing apple trees in a Mediterranean climate, South Africa. 30th international horticultural congress, Istanbul Turkey, pp. 12–16Google Scholar
- Nyoni M (2018) Spectrum of in vitro activity and efficacy of phosphonates for management of apple replant disease and oomycete root rot pathogens in South Africa. PhD dissertation, Stellenbosch University, South AfricaGoogle Scholar
- Thomas G (2008) Using phosphonates effectively to control Phytophthora root rot in avocados. Talking Avocados 2008:33–34Google Scholar
- Van der Merwe M, Kotze J (1994) Fungicidal action of phosphite in avocado root tips on Phytophthora cinnamomi. SAAG Y 17:38–45Google Scholar
- Van Zyl FJ (2016) Quantifying root growth dynamics and nutrient uptake in apple trees. MSc Agric thesis. Faculty of Agriculture, Stellenbosch University, South AfricaGoogle Scholar