Symptoms: The new leaves turn yellow except for the veins, and the leaf yellowing leaves grow on the axillary buds.
Occurrence conditions: (1) The soil is prone to iron deficiency due to its high phosphorus content and high pH. (2) Due to the excessive amount of phosphate fertilizer, iron absorption is affected, and iron deficiency is also prone to occur. (3) When the soil is too dry, too humid, and low temperature, iron deficiency may also occur due to the influence of the root activity. (4) When copper and manganese are too much, it is easy to produce an antagonistic effect with iron, and iron deficiency symptoms occur.
Diagnosis points: (1) According to the judgment of the depth of the veins of the veins, if it is dark green, there is a possibility of lack of manganese; if it is light or pale, fade is iron deficiency, which can be confirmed according to the above conditions. (2) Determine the soil pH. If the pH is high, the possibility of iron deficiency is high. (3) Similar symptoms may occur when the root function declines due to other reasons. (4) There are not many similar symptoms due to insect pests.
Control measures: (1) When the pH reaches 6.5-6.7, the use of alkaline fertilizers and the use of physiological acidic fertilizers are prohibited. When there is too much phosphorus in the soil, deep plowing, soil and other methods can be used to reduce the content. (2) Emergency measures: If iron deficiency symptoms have appeared, spray the tomato with a solution of 0.5%-0.1% ferrous sulfate in water, or spray 2-3 times with lemon iron 100 mg/kg per week.
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