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Tomato - Chlorosis
Symptoms
Symptoms of magnesium deficiency start on older leaves. They show interveinal chlorosis on the leaf margins and some whitish to light brown necrotic dots.
If deficiency is severe, interveinal chlorosis progresses from the margins to the middle of the leaflets. The small veins also become chlorotic, but the bigger veins remain dark green first.
Subsequently the whole leaves are yellowing and finally the older leaves die. In this case growth is severely impaired and fruit yield is reduced.
Reasons
Magnesium deficiency
Magnesium uptake can be depressed by an excess of other cations (potassium, ammonim, calcium).
Symptom can be confused with nitrogen and iron deficiency. But in the case of nitrogen deficiency the whole leaf turns uniformly yellow and the veins do not remain green.
Iron deficient plants also show intercostal chlorosis, but in contrast to Mg it starts on the young leaves.
Magnesium deficiency made worse by
- Sandy soils
- Acidic soils
- Potassium rich soils
- Soils receiving high potash applications
- Cold wet periods
Magnesium is important for
- Part of chlorophyll molecule
- Phosphate metabolism
- Nitrogen metabolism
- Protein synthesis
- Water uptake by the plant