The yellowing and abnormality of the leaves of vegetables are not caused by infective diseases, which is a physiological hazard. The occurrence of such harm reflects that there are some misunderstandings in the management process, and we must adjust the management methods in time to avoid further harm. The main reasons are as follows.
Calcium deficiency: Calcium plays a very important role in the growth of melons and fruits. If the metabolism of calcium is imbalanced, it will easily cause the leaf margin of the upper and middle leaves to turn yellow, and the edge of the leaf will roll down to form a parachute leaf. If the calcium deficiency is very serious, during the low-temperature cultivation process, the new leaves of the melon crops (especially cucumber) grow yellow and dry. Prevention and treatment methods: To prevent calcium deficiency, especially in high temperature and drought, as well as in early spring and deep winter cultivation, fruits and vegetables need sufficient calcium fertilizer in the peak period. It is recommended to use chelated calcium fertilizer for foliar spray. The fertilizer effect is good. It is best to supplement the calcium and boron to promote mutual absorption.
The temperature is too low or too high: the temperature of the greenhouse is too low, the leaves become brittle, and the leaf edge will also yellow, and the parachute leaves can also be formed. When the temperature is too high, the leaf edge water evaporates quickly, which can cause the leaf edge to burn and yellow and dry. Control method: balance the temperature of the greenhouse, combined with foliar spray chitin, alizarin and other conditioning agents, preferably with potassium dihydrogen phosphate.
Deterioration of the soil environment: Excessive use of chemical fertilizers in successive years can lead to soil compaction, soil salinization, poor root development, and gold margins on the leaf margins. Control methods: comprehensively improve the soil, apply sufficient organic fertilizer and biological fertilizer to the base fertilizer, improve the soil; pay attention to the application of chitin, fulvic acid, alginic acid and other root-grown fertilizers.
Phytotoxicity: If the dosage is too large, or if the drug is caused by high temperature, the leaf edge will turn yellow, and the serious one will harm the flower and fruit, including the harm of aerosol. Control methods: foliar spray of nucleotides and cytokinins to alleviate the damage.
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