symptom
At the beginning, yellowing between the veins appears on the rapidly expanding young leaves, and the leaves are blue-yellow or have green veins, and then the leaves turn yellowish like ivory or white, and the severely chlorotic parts of the leaves often turn brown and necrotic. The growth of new shoots is significantly reduced, the flower spikes and cobs turn light yellow, and there is less fruit setting. In terms of production, if the iron deficiency situation is changed in time, the growth of new shoots will turn green, but the color of old leaves that develop earlier will recover slowly.
Etiology
The role of iron is to promote the activity of various enzymes. When iron is deficient, the formation of chlorophyll is affected, resulting in leaf chlorosis. In the field, iron exists in the soil as compounds such as oxides, hydroxides, phosphates, and silicates. When these inorganic salts are decomposed, a small amount of iron is released, which is absorbed by roots in the form of ions or compound organic matter. Iron deficiency is certain, but sometimes soil conditions limit iron uptake by roots, such as clay, poorly drained soil, low soil temperature, or increased salinity can easily cause insufficient iron supply. Especially in cold spring, high humidity or sudden rise in temperature in late spring, the rapid growth of new shoots can easily induce iron deficiency. Since iron moves to the required parts in the grape body as iron ions, it combines with proteins to form complex organic compounds. Iron cannot move from one tissue to another in grapes, so new shoots or newly expanded leaves are prone to symptoms.
During production, since iron is easily fixed or combined into compounds that cannot be utilized, the detection of total iron content and iron deficiency may not correspond to each other, so it is difficult to diagnose.
Prevention method
(1) To strengthen the management of the vineyard, watering in early spring should try to extend the water flow distance to increase the water temperature and ground temperature.
(2) Timely loosen the soil, increase the application of organic fertilizers, and reduce the salt content of the soil.
(3) Spray ferrous sulfate on the leaves, add 5-7g of ferrous sulfate per liter of water, and spray again after 15-20 days. In addition, after pruning, 200-250g of ferrous sulfate can be added to each liter of water, and it is also effective to smear the branches above the terminal buds after pruning.
