Preliminary Observations in Blocks Using PAD to Delay the First Apple Scab Fungicide Spray

Apple growers in the Northeast apply more sprays to manage apple scab than to manage any other disease or any insect problem. Reducing fungicide use in recent years has been difficult for all commercial apple growers. The introduction of the demethylation- inhibitor fungicides, also called sterol inhibitors (DMIs or SIs) fungicides (Nova/Rally, Rubigan, and Procure) in the 1980s allowed growers to adopt a "four-spray" program to manage apple scab. Using DMIs in combination with a protectant fungicide, usually captan or mancozeb, a grower could delay the initial fungicide application until the half-inch green or early tight cluster bud stage, and make subsequent applications at approximately 10-day intervals through to fruit set. Compare this to a typical program for apple scab before the introduction of DMIs. Programs commonly started at bud break, and continued with sprays every five to seven days through to fruit set, typically requiring five to seven fungicide applications. In other words, DMI fungicides allowed growers to save one to three applications a year. Unfortunately the apple scab fungus has developed wide-spread resistance to DMIs. With this, growers have been forced to return to using fungicides that need to be applied more frequently, either the older protectants or newer fungicides. As a result, the amounts of fungicides applied in apple orchards today have increased compared to levels used five to fifteen years ago. New England growers and plant pathologists have collaborated to develop a strategy that can reduce the total number of sprays per season by 2 or 3, and that can allow for better integration of fungicide and insecticide applications at the tight cluster bud stage. The method was developed and tested first in New Hampshire, and simplified by researchers in Vermont