Symptoms
Symptoms of magnesium deficiency start on older leaves. They show interveinal chlorosis, often covered with some whitish, necrotic dots. In the beginning, the spots may also have an olive green, watery and sunken appearence.
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.
The necroses become larger.
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.
