Occurrence Patterns and Control Methods of Zinc Deficiency in Apple Trees

Apple trees are highly susceptible to diseases during cultivation, especially physiological diseases caused by zinc deficiency, which we also call little leaf disease. The occurrence of this disease can cause apple tree leaves to turn yellow or grow relatively small. Let us take a look below at the occurrence and control of zinc deficiency in apple trees.

I. Symptoms of zinc deficiency in apple trees

Zinc deficiency in apple trees mainly shows on new shoots and leaves, and is especially prominent on the terminal shoots at the outer part of the canopy. In spring, diseased branches bud late, the internodes of new shoots become shorter, and the leaves are small and clustered, forming a rosette shape. Diseased leaves are narrow, small and slender, hard and brittle, with the leaf margins curling upward; the leaves are yellow-green or uneven in shade, and the leaf veins become lighter in color. Diseased trees have fewer flower buds, small and pale flowers, and a low fruit-setting rate or small, deformed fruit. On severely diseased trees, leaves gradually fall from the base of the new shoots upward, the canopy becomes hollow, the root system develops poorly, and root rot is likely to occur.

II. Control measures for zinc deficiency in apple trees

1. Control virus transmission and reduce the harm of little leaf disease caused by viruses: For little leaf disease caused by viruses, virus transmission must be strictly controlled in production to prevent the spread of little leaf disease. If little leaf disease is confirmed to be caused by a virus, affected plants should be promptly dug out. If the damage is relatively mild, use dedicated tools during pruning to prevent virus transmission, and at the same time spray diseased plants in a targeted manner with agents such as Virus Ling for correction.

2. Apply targeted supplementation to overcome nutrient deficiency and promote robust leaf growth: For little leaf symptoms caused by nutrient deficiency, carefully study the symptoms in production, treat them according to the cause, and overcome the adverse effects of nutrient deficiency. For little leaf caused by nitrogen deficiency, increase the application of organic fertilizer and supplement nitrogen fertilizer, especially quick-acting nitrogen fertilizer, to promote the leaves to return to normal. While applying nitrogen fertilizer to the roots, foliar spraying of 0.3%-0.5% urea can be used for correction; for little leaf caused by phosphorus deficiency, on the basis of increasing organic fertilizer application, pay attention to increasing the application rate of phosphorus fertilizer to supplement the phosphorus content in the soil and improve the phosphorus supply capacity, and 0.3%-0.5% monopotassium phosphate can be sprayed on the leaves; for little leaf caused by zinc deficiency, when applying base fertilizer, according to tree size, add 0.5-1 kg of zinc sulfate per tree. In early spring before the tree body sprouts, spray 0.3% zinc sulfate + 0.3% urea on the trunk and main branches. After sprouting, spray the leaves 1-2 times with 0.3%-0.5% zinc sulfate solution for correction. According to practice, adding 0.2%-0.3% urea when spraying zinc on the leaves makes it more likely to be effective.

3. Select excellent varieties for orchard establishment. When establishing an orchard, choose varieties with relatively strong comprehensive resistance, such as Red Fuji and Delicious strains, and choose a site with high terrain, good drainage, sunny conditions, and good ventilation for orchard establishment. In addition, do not establish another apple orchard on replanted orchard land or nursery land.

4. Deep plow the soil and increase organic fertilizer application to promote robust root growth, improve the absorption function of the tree body, and facilitate robust leaf growth: For terraced orchards, pay attention to deep plowing before orchard establishment. If deep plowing was not done at the time of orchard establishment, then within 2-5 years after planting the trees, carry out one deep plowing of the entire orchard, especially the places where soil has been removed, which must be deep plowed. Ensure the deep plowing depth is more than 60 cm. If a large amount of organic fertilizer can be applied in combination with deep plowing, it can optimize the rhizosphere growth environment and will have an obvious effect on correcting the occurrence of little leaf symptoms.

5. Chemical control. According to the zinc requirement characteristics of apple trees, supplementing zinc fertilizer can effectively control the occurrence of zinc deficiency in apple trees. In combination with autumn base fertilizer application, add 0.5-1 kg of zinc sulfate per mature tree. It takes effect the following year and has a long lasting effect, but it is less effective in alkaline soil, so foliar zinc spraying should be carried out. Before the fruit tree leaf buds begin to swell but before sprouting, spray 3%-5% zinc sulfate solution, or after sprouting spray 0.1% zinc sulfate solution. Because nitrogen can promote zinc absorption, 20 days after full bloom of apple trees, spray 0.2% zinc sulfate plus 0.3% urea solution, which has a good effect on reducing symptoms.