Morgan L. Cromwell1, Lorraine P. Berkett and Heather M. Darby from the Department of Plant and Soil Science, University of Vermont, and Takamaru Ashikaga from Medical Biostatistics, University of Vermont, did a trial evaluation of organic fungicides for apple tree scab.
They tested three potential alternative fungicides along with the standard treatment (lime/sulfure) and a control group of no treatment.
- potassium bicarbonate (PB),
- neem oil (NO), and
- Bacillus subtilis (Bs)] with a
- standard organic sulfur/lime sulfur (SLS) fungicide program and a
- non-treated control (NTC)
The five treatments were applied to ‘Empire’ trees arranged in a completely randomized design with five single-tree replications at the University of Vermont Horticultural Research Center in South Burlington, VT
Fungicides were applied with a handgun to drip using maximum label rates.
Applications began on 26 Apr. 2007 and 23 Apr. 2008 and continued on approximately a weekly schedule through the end of June and then every 2 weeks through 23 July 2007 and 17 July 2008, respectively
The standard SLS treatment resulted in the best scab control in both years.
The Neem treatment reduced foliar and fruit scab compared with the Control and the other alternatives at the end of the 2008 growing season and had insecticidal activity.
However, both the Standard Lime Sulfur and Neem treatments had disadvantages, including phytotoxic burning on the fruit and/or significantly more russeting on the fruit at harvest.
In each year of the study, one or more of the alternative treatments, particularly Bt, resulted in higher insect damage than the non-fungicide-treated control.
This research showed that the tested alternatives do not offer advantages over the standard Lime Sulfur fungicide program in organic apple production and in some cases offer distinct disadvantages
Lime sulfur is still the best control for apple scab on the organic backyard fruit garden. Read and follow the directions on the label re timing in your area.
From the American Society for Horticultural Science