You can double-dip in disease prevention with this early-season copper application as copper compounds, although not quite as effective as Captan or EBDCs for apple scab control, can play a role in scab management as the first spray of the season at 0.25- to 0.5-inch green tip. Copper, at 2 pounds metallic equivalent per acre, represents a separate mode of action that is not at risk of resistance development.

The green tip timing is absolutely critical for apple scab management. Although the amount of tissue available for infection is small and the scab spore load is typically small at this early timing, any infection that occurs early will result in severe consequences later in the primary scab season. This is because lesions initiated at green tip will be producing secondary spores (conidia) at a timing between pink and petal fall that coincides with what is typically the period of highest primary spore concentration from overwintering leaves. Thus, early infections can be a killer because they compound the spore load in an orchard, which can lead to significant fruit infection. It is true there is not a lot of green tissue present in orchards at green tip. But, be certain that spores of the scab fungus can find that tissue; for any spores released at this timing, that is their primary function. And once they land on that susceptible tissue, infection, producing a lesion and conidia becomes the primary function.

Finally, beware of phytotoxicity!

Copper phytotoxicity can occur on apples, with the predominant copper problem on apples being increased fruit russeting. Although phytotoxicity is a potential problem, if used wisely, copper bactericides applied early will effectively begin the 2012 disease management season and lower primary fire blight disease inoculum and control early apple scab.