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United States Department of Agriculture

Agricultural Research Service

Title: Evaluation of Fungicide Programs for Management of Apple Scab and Powdery Mildew, 2004

Authors
item Turechek, William
item Heidenreich, M - CORNELL UNIVERSITY
item Heidenreich, G - CORNELL UNIVERSITY

Submitted to: Fungicide and Nematocide Tests
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 31, 2005
Publication Date: April 1, 2005
Citation: Turechek, W., Heidenreich, M.C., Heidenreich, G. 2005. Evaluation of fungicide programs for management of apple scab and powdery mildew. Fungicide and Nematocide Tests. 60:PF028.

Interpretive Summary: Apple scab is the most important fungal disease of apple worldwide. To maintain consistent protection from apple scab through high risk periods, growers typically apply fungicides on a 7 to 10 day schedule resulting in 10 to 15 regular applications. Despite their best intentions, growers often encounter control failures. Some of these failures can be attributed to the absence of fungicides with suitable 'kickback' activity (i.e., the ability to eradicate an existing infection) and/or the presence of fungicide resistant strains of the fungus. A field trial was designed to evaluate fungicide programs that address these causes of control failures. Results showed that programs can be designed to effectively manage fungicide resistance while achieving commercially acceptable levels of control. However, we found it difficult to achieve superior scab control with programs that included a fungicide with significant kickback activity; this may be attributed to factors outside the inherent activity of the fungicide. This i

Technical Abstract: Apple scab, caused by the fungus Venturia inaequalis, is the most important fungal disease of apple worldwide. The disease is managed primarily through the timely application of fungicides. To maintain consistent protection from apple scab through high risk periods, growers typically apply fungicides on a 7 to 10 day schedule, or after 2-3 inches of rainfall, resulting in 10 to 15 regular applications. Despite their best intentions, growers often encounter control failures. Some of these failures can be attributed to poorly-timed applications, the absence of fungicides with suitable 'kickback' activity (i.e., the ability to eradicate an existing infection), and the presence of fungicide resistant strains of the fungus. A field trial was designed to evaluate fungicide programs that address the causes of control failures. In this trial, we evaluated programs that use strobilurin fungicides applied at their highest and lowest labeled rates and as a mixture of the lowest labeled rate with a contact fungicide in commercial spray programs for their efficacy against apple scab as well as their utility in a resistance management program. Our results showed that anti-resistance properties of high strobilurin rates are superior to low rates and low rate mixtures with a protectant fungicide. We further evaluated programs that incorporate Scala (pyrimethanil) or Dodine as early-season sprays for their eradicant properties. The results showed that programs that included Scala provided good control of foliar scab, the degree of control was generally not statistically better than programs which did not include a fungicide with significant kickback activity. Programs that included Dodine failed to provide better control of scab, and even had slightly higher levels of scab than comparable programs; we suspect the presence of Dodine resistant isolates. Obtaining consistent results in our powdery mildew trials was challenging as none of the treatments performed statistically better than the control.

Last Modified: 10/1/2014
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