1. Use a fertilizer that contains Cu.
2. Correct by applying a fungicidal spray containing copper, such as tri-basic copper sulfate if needed.
3. Corrective drench application of copper sulfate at 9.3 ppm of Cu for soilless substrates. Add 0.5 oz. (14.2 g) of copper sulfate (25% Cu) per 100 gallons of water. Do not over apply. Rinse off foliage.
4. Foliar spray of Cu: mix 4 oz. (113.4 g) of tri-basic copper sulfate per 100 gallons of water. It will give a final concentration of 159 ppm Cu. Test on a few plants first. Do not over apply.

Foliar sprays have a greater risk of plant injury. Avoid applications during the midday heat. Plant uptake is enhanced by prolonged drying time, which occurs during humid conditions, especially in the morning. Nutrient uptake through the leaves is also greater in the day than at night, making morning applications more desirable than evening sprays.