Copper's mode of action is not unlike a piano being dropped from a four-story building and landing on you. Applying fixed copper early gets this mineral into bud scales and twig lesions where pathogens might be lingering. Of course, so are benign microbes, and that's why it's important to understand the specifics of the disease(s) at your site if playing this card:
Apple Scab - Copper can be useful in a "dirty orchard" to protect green tissue as buds unfurl. Conidia overwinter in the buds in warmer zones and must be dealt with. Further north, it's residual copper spreading into tissue moisture pockets that undoes the first round of spores. These earliest potential infections are not so much a concern for growers enhancing leaf decomposition.
Pear scab is a little different, however, as twig lesions in the tree are an "up high" source of inoculum.
Peach Leaf Curl - A fixed copper application made in fall when leaves come off the tree and again in late winter is a proven allopathic approach to knocking back these fungi. Same goes for
Bacterial Spot. Different microbe but same overwintering haven.
Brown Rot - These fungal pathogens of stone fruit build in number over the course of several years. The primary overwintering sites are mummified fruit both in the tree and on the ground, along with cankers at the base of buds. Copper plays a role in regaining the upper hand where rot has become severe. The primary window (as I understand it) is definitely a dormant application, and here spray the ground beneath the tree as well, followed with one or two additional copper soap apps up till pink (think peach pink) but not beyond. This applies to the "blossom blight" phase which in turn sets up the fruit rot phase. This is not something to do every year but rather to get back to square one.
Cedar Apple Rust - Copper has no relevance whatsoever. The spores-to-come are on an entirely different tree (the eastern red cedar) at quarter-inch-green on the apple. Plus this fungal disease is a couple beats behind scab so even residual copper will be gone when the primary infection period for rust begins.
Fire Blight - Copper's role here is to literally capture all staging areas throughout the orchard on both well trees and susceptible trees. The bacterium that causes fire blight spreads from cankers early in the season but can't infect until conditions are right during bloom and beyond. The heavy metal strategy in this case is preemptive.
Mike makes great points about knowing copper levels in your soil and the interaction between one strategy and the next. I have not sprayed copper for 20 years now for disease purpose but would certainly consider it if an overwhelming situation develops. Otherwise, that "blue piano" is also wiping out the very microbes that work in the fruit grower's favor on the competitive colonization front.
And just because Roger started all this ... use of dormant oil at a 2% concentration with a fixed copper as a dormant application helps spread the mineral deeper into those bud scales and crevices. There are different formulations of "safe copper" once the growing season has begun.
Lost Nation OrchardZone 4b in New Hampshire
Edited 1 time(s). Last edit at 04/10/2014 09:56AM by Michael Phillips.