Manganese (Mn)

Function:

Manganese (Mn) is involved with oxidation-reduction in electron transport.

Deficiency:

Deficiency symptoms are expressed on young mature growth as a mottled, interveinal chlorosis (yellowing), which progresses to a necrotic (brown) areas on young leaves. (Mn deficiency and iron deficiency both have similar symptoms.) It is important to correct Mn deficiency when symptoms first appear because leaf necrosis can not be reversed. Mn is relatively immobile in the plant and deficiency symptoms appear on the young, newly developing leaves. Excessive levels of Ca or Mg can have an antagonistic effect on Mn availability.

Excess:

Symptoms appear on the older leaves as leaf yellowing and leaf margin necrosis. Excessive levels of Mn can become available at pHs <5.4.

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

Monitoring and Management Strategy for Manganese (Mn)

Fertilization Rate:

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

Interactions:

Excessive levels of Ca or Mg can have an antagonistic effect on Cu availability. Excessive levels of Mn can become available at pHs <5.4.

Tissue Concentration:

Normal range is 60 to 300 ppm. Levels below 40 ppm are considered deficient and above 650 are considered toxic.

Options:

Preplant:

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

Continual Fertilization:

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

Corrective Fertilization:

1. Corrective applications of manganese sulfate at 10 ppm of Mn (see mixing rates below) for soilless substrates. A corrective fertilization of Mn will return the tissue to the normal green color within 1 to 2 weeks. It is important to correct Mn deficiency when symptoms first appear because leaf necrosis can not be reversed.

   For Corrective Application: Add 0.5 oz. (14.2 g) of manganese sulfate (28% Mn) 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.

To apply a foliar spray of Mn: mix 2 oz. (56.7 g) of manganese sulfate per 100 gallons of water. It will give a final concentration of 40 ppm Mn. Test on a few plants first. Do not over apply.

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