By Erica Faber – Orchard Productivity Manager
Excessive copper can affect the uptake of phosphorus, zinc, manganese and iron, resulting in low levels within the plant contributing to poorer performance and yield. High levels of copper have also been found to inhibit root growth as well as have an adverse effect on beneficial fungi (which suppress phytophthora), bacteria, protozoa and earthworms. Copper-based fungicides however are an effective means of improving packouts and returns by controlling fungal diseases such as anthracnose, post-harvest rots etc. Until alternative, effective controls are found, it seems they are our only option. So, what can we as growers do to ensure we try minimize these negative side effects.
These are some suggestions for avoiding elevated levels of copper and their side effects within our orchards:
Firstly, by managing orchard sanitation, we can reduce the source of fungal inoculum in orchards by chipping or mulching the old prunings and by removing windfall fruit from the orchard floor. This will lower the incidence of anthracnose and post-harvest rots and will reduce the amount of copper sprays eventually required for the control of these fungal diseases.
Pruning also plays an integral part in reducing the severity of these fungal diseases by allowing better air movement throughout the canopy, thereby improving drying conditions.
Calcium sprays onto young developing fruit will be absorbed by the fruit and ensure improved fruit quality as well as strengthened cell walls. These strengthened cell walls are more resilient to penetration of the fungal hyphae as well as post-harvest bruising. Remember though that Boron also affects calcium absorption, so this needs to be in balance for the calcium to be effective.
Limit the copper ion concentration on plant surfaces by using copper products that are relatively insoluble in water, i.e. fixed copper.