When to apply the first walnut blight treatment ?

For over 30 years, attempts have been made to determine when to begin treating for walnut blight, Xanthomonas campestris pv. juglandis. Past trial results have always indicated that the best time to begin treating was just before significant moisture, usually in the form of rain, occurred. Without some control over the amount of moisture present, the time to begin treating could not be tied to tree physiology but only to environmental conditions. The advent of overhead sprinklers in the test orchard, which has allowed researchers to create “rain” at will, has provided progress in addressing the question of what physiological stage of tree development is most desirable before applying the first walnut blight treatment in the spring.