The model predicts ascospore maturation based on degree days accumulated from the green-tip bud stage on apples. Thus, on the graphs shown below, the beginning of each graphed line toward the lower left corner indicates the dates for green-tip on McIntosh for the respective years. The most striking observation from the graph below is that apple scab ascospore development occurred roughly two weeks later during every year from 1992 to 1996, compared with the years from 1987 to 1991. The most striking observation we found from this exercise is that apple scab ascospore development occurred roughly two weeks later during every year from 1992 to 1996, compared with the years from 1987 to 1991. In the Hudson Valley, we have benefited from late springs during each of the past five years.
Late springs allow more time to get sprayers up and running and clear brush from the orchards.
Often, a late spring also means that fewer fungicide sprays will be needed prior to bloom because tree development may be more rapid when spring finally arrives. This could be the year that we revert to the spring weather patterns we had from 1987-1991. With high inoculum levels, it will be essential to get into the orchards and get a scab fungicide applied at green-tip. As we've said in the past, there may be times when you don't get the expected results from a pesticide application, even though you used the correct concentration of the recommended material and applied it in the same way that has given acceptable control at other times. A close inspection of the pesticide label will often reveal a caution against mixing the chemical with alkaline materials such as lime or lime sulfur.