Fall is well upon us in the Okanagan and the apple harvest is starting to slow down. This is historically seen as a quieter time for growers, as fruit trees start shifting into a state of dormancy, yet this may be one of the most crucial times to think about tree fruit care as well as preventative measures for the upcoming seasons.
Now is a good time to start spraying your fruit trees and one of the sprays you should consider using is fixed copper, which includes copper oxide, copper oxychloride, copper hydroxide and copper ions linked to fatty acids or other organic molecules (Cueva).
What is Fixed Copper?
Copper Sulfate has a high solubility in water and can therefore cause phytotoxicity even at relatively low application rates. The high solubility also means that copper sulfate residues can be rapidly removed by rainfall. Copper products registered for tree fruits are almost all fixed coppers that have low solubility in water. When mixed with water, the spray solution is actually a suspension of copper particles, and those particles persist on plant surfaces after the spray dries. Copper ions are gradually released from these copper deposits each time the plant surface becomes wet. The gradual release of copper ions from the copper deposits provides residual protection against plant pathogens. At the same time, the slow release of copper ions from these relatively insoluble copper deposits reduces risks of phytotoxicity to plant tissues.
Why Use Fixed Copper?
When used correctly, fixed copper sprays will cut costs and effectively help to manage bacteria and fungi on your fruit trees, stone fruit and pome fruit. Copper sprays help to manage bacteria and fungi such as fireblight and bacterial canker as well as bacterial spot and fungal diseases like cherry leaf spot, peach leaf curl, and apple scab as well.
Some Tips and Important Information to Remember when Applying Fixed Copper in the Fall
- Copper sprays act as protectant against fungicide and bacteria rather than a treatment for already present bacteria and fungi and should always be applied in a preventative way.
- Fixed copper is moderately toxic to bees, and should only be applied in the late evening or early morning when bees are not foraging for food.
- Copper does not break down in the soil. A buildup of excess copper is toxic to earthworms, and runoff of copper-based fungicides pollutes water.
- Except for Cueva, always apply fixed copper before green tissue emerged or after harvest.
- Different formulations have different properties and should be applied accordingly. The rate per acre varies widely and not all formulations are registered on all tree fruits. Some fixed copper products do not have the same diseases listed on their labels, so always ensure you’re reading labels carefully or ask for an expert’s help before using a copper product.
Besides fixed copper sprays, post-harvest sprays of Boron, Zinc, Magnesium and Urea should be used too to facilitate strong buds in the next growing season. Always keep in mind that you need good leaf function after the application for the nutrients to be translocated down into the storage tissues. In other words, the leaves need to be green and not yet turning yellow.