Copper (Cu)

Function:

Copper (Cu) is a component of several enzyme complexes, pollen formation, and fertilization.

Deficiency:

Deficiency symptoms are expressed on young growth as chlorosis, with leaves becoming distorted or cupped. It is important to correct Cu deficiency when symptoms first appear because distorted leaves can not be reversed. Copper is immobile and deficiency symptoms appear with the young, newly developing leaves. Excessive levels of K or P can have an antagonistic effect on Cu availability.

Excess:

Symptoms vary, but can cause death of roots (lack of lateral root development) and plant decline. Excessive levels of Cu can have an antagonistic effect on Fe, Mo, or Zn availability.

Confirm your actual Cu levels by conducting a plant tissue analysis. Root substrate (medium) tests are less reliable for determining Cu levels.

Monitoring and Management Strategy for Copper (Cu)

Fertilization Rate:

There is a fine line between deficient and toxic levels. Use a fertilizer that provides a measured dose of Cu.

Interactions:

Excessive levels of K or P can have an antagonistic effect on Cu availability. Excessive levels of Cu can have an antagonistic effect on Fe, Mo, or Zn availability.

Tissue Concentration:

Normal range is 2 to 10 ppm. Levels below 1 ppm are considered deficient and above 15 are considered excessive.

Options:

Preplant:

Incorporation of a micro-nutrient mix into your soilless substrate.

Continual Fertilization:

Most commercial fertilizers that provide micronutrients including Cu. Remember to add supplemental Cu applications if using calcium nitrate (Ca(NO₃)₂) + potassium nitrate (KNO₃).

Corrective Fertilization:

1. Correct by applying a fungicidal spray containing copper, such as Bordeaux mixture.
2. Corrective applications of copper sulfate at 9.3 ppm of Cu (see mixing rates below) for soilless substrates. A corrective fertilization of Cu will return the tissue to the normal green color within 1 to 2 weeks. It is important to correct Cu deficiency when symptoms first appear because distorted or cupped leaves can not be reversed.

   For Corrective Application: Add 0.5 oz. (14.2 g) of copper sulfate (25% Cu) per 100 gallons of water. Do not over apply.

Corrective Foliar Spray:

Foliar sprays have a greater risk of plant injury. Early morning applications are preferred. Avoid applications during the midday heat. Plant uptake is enhanced by the increased drying time which occurs during the moist conditions in the morning. Nutrient uptake through the leaves is also greater in the light periods than at night, thus making morning applications more desirable than evening sprays.

1. Correct by applying a fungicidal spray containing copper, such as Bordeaux mixture.
2. To apply a 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.

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