Manganese is an essential trace element for all plants. Manganese acts as an activator for different enzyme reactions in the plant, for example in water-splitting during photosynthesis, the synthesis of amino acids and proteins and the build up of plant cell membranes and chloroplasts. Manganese is generally taken up via the roots.
Once inside the plant it is difficult to transport but not as difficult as calcium or iron for example. Silicon and molybdenum improve the transport possibilities for manganese in the plant.
About manganese in short
- What is it and what does it do?
- The metal manganese is an essential trace nutrient and acts as an activator for different enzyme reactions in the plant.
- What can you see?
- Yellow stripes appear between the leaf’s side veins.
- What can you do?
- Using products that contain trace elements (Tracemix).
Symptoms of a deficiency
A manganese deficiency causes different physiological changes in the plant due to a decrease in protein production. Amongst others, this causes less nitrate to be fixed in the plant, which can lead to dangerously high levels of nitrate. Additionally, a lot of chemical reactions in plant cells slow down which may result in a build up of organic acids.
Development of a deficiency
The progression in chronological order:
- Yellow stripes appear between the leaf’s side veins on the larger leaves at the top of the plant.
- The yellowing between the side veins spreads further over the leaf and small, yellow/brown necrotic spots can form.
- The final result is a small plant (-10%) with minimum fruit/flower production.
Reasons for a deficiency
In practice, the most common reason is that the pH in the substrate is too high. Like iron, manganese is easily dissolved at a low pH value in the substrate. If the pH is too low, a risk of excess manganese may occur. At high pH values manganese precipitates into manganese oxide (MnO2) which cannot be taken up by the plant which can cause deficiency.
Solutions to resolve a deficiency
- Check the medium’s pH when the first symptoms are noticed. High pH values mean that there is less manganese available for the plant. By lowering the pH of the nutrition (pH min (down)) the medium’s pH can be lowered to 5.0-5.5.
- Low substrate temperature can be the cause of reduced manganese absorption. If a deficiency is noticed, check that the substrate temperature is sufficiently high (20-25ºC) during the day.
- Using products that contain trace elements (Tracemix) may also help. A manganese deficiency is usually not a problem on its own. To facilitate manganese transportation in the plant, molybdenum is needed. Thus, the problem may well be a molybdenum deficiency. High levels of phosphorus may also result in a reduced availability of trace elements like zinc, copper and (of course) manganese. CANNA advises to use a mix of all needed trace elements. Trace elements can be given to the plant both in the feeding and by spraying the leaves. Spray the plant at the end of the day and spray daily with water after spraying to prevent burning.
When there are high concentrations, manganese precipitates into manganese oxide (MnO2 or black manganese) which causes yellow- brown spots on the leaves. Initially, small spots will appear along the main and side veins of the leaf, following this the spots will spread out from the veins. Excess manganese can be a result of a low pH in the substrate (<5.0), this can be corrected with pH plus (up). Oxygen deficiency in the root environment can also cause excess manganese. A substrate that is too wet can be a cause.