Occurrence Patterns and Control Methods of Jujube Fruit Shrink Disease

I. Symptoms and Damage

Jujube fruit shrink disease, also known as jujube fruit wilt disease, jujube fog wilt disease, etc., is one of the major diseases in all major jujube-growing regions of China. In jujube fruits affected by fruit shrink disease, yellow-brown irregular discolored spots first appear on the fruit shoulder or body, then the fruit skin becomes water-soaked and earthy yellow with indistinct edges, and later the fruit skin turns dark red, shrinks, and loses its luster. In the diseased area of the flesh, brown spots and earthy yellow softness appear from the outside inward. Diseased fruits taste bitter. The fruit stalk turns brown or dark brown. The entire diseased fruit is shrunken and small, and falls off before maturity. After the pathogen of jujube fruit shrink disease invades a normal fruit, the disease symptoms of the infected fruit generally go through several stages: halo, water soaking, coloring, shrinking, and falling off, but this is not always the case. If fruit shrink disease occurs in the early growth stage of jujube fruit, the diseased fruit falls off at the water-soaking stage; if fruit shrink disease occurs in the middle growth stage, some diseased fruits fall off when they are half red; and if fruit shrink disease occurs in the late growth stage of jujube fruit, most diseased fruits enter the harvest period without falling off at the shrinking stage.

II. Occurrence Patterns

Research in recent years has shown that fruit shrink disease is caused by bacterial infection. Its occurrence is directly related to damage to the outer skin of jujube fruits. In addition to wounds from natural wear on jujube fruits being able to transmit the disease, the disease is mainly transmitted through wounds caused by piercing-sucking mouthpart pests such as mites, leafhoppers, and stink bugs. The occurrence of the disease is also related to the developmental stage of jujube fruits. In North China, the disease generally occurs when jujube fruits turn white and begin to color. In terms of climatic conditions, when the temperature is 26°C to 28°C, once continuous rainy weather or rainy nights with clear days occurs, this disease is prone to breaking out into a disaster. Fruit shrink disease occurs mostly in spots and patches; in one jujube orchard, several trees are often severely affected, and on one jujube tree, several branches are often severely affected. In addition, fruit shrink disease often occurs on the same jujube fruit together with anthracnose or occurs in the same jujube orchard at the same time, and sometimes it is relatively difficult to distinguish them. The main difference between the two kinds of diseased fruit lies in whether the jujube pit turns black. In jujube fruits affected only by fruit shrink disease, the pit generally does not change color, but once infected with anthracnose, the pit will turn black.

III. Control Techniques

1. Strengthen pest control work and promptly prevent the occurrence and damage of piercing-sucking pests, such as peach fruit borer, scale insects, stink bugs, mites, and leafhoppers. Spray insecticides in the early stage, mainly to control jujube bud-eating weevils, leafhoppers, and jujube geometrid moths; in the later stage from August to September, in combination with insect control, apply insecticides such as cypermethrin mixed with tebuconazole (diclobutrazol) for spraying, and the control effect on jujube fruit shrink disease can reach more than 95%.

2. Strengthen orchard soil management, and keep the soil moist during the period when jujube fruits change color and turn red, to prevent or reduce the occurrence of fruit cracking.

3. Before and after jujube fruits change color and turn red, spray "Jujube Fruit Anti-Cracking and Anti-Rot Agent" (developed by Cangzhou Academy of Agriculture and Forestry Sciences) to prevent fruit cracking and reduce the number of cracked fruits. Each tube is 10 milliliters, directly diluted with 25 to 30 kilograms of water and sprayed over the whole tree, once every 7 to 10 days, for 2 to 3 consecutive applications.

4. Before and after the onset of disease during the period when jujube fruits change color and turn red, spray 50% DT fungicide at 500 times dilution or 12.5% tebuconazole powder at 3000 times dilution, once every 7 to 10 days, for 3 to 4 consecutive sprays. Use streptomycin at 200 international units per milliliter (that is, 10 million international units diluted with 50 kilograms of water) or oxytetracycline at 200 international units per milliliter, or kendomycin at 140 units per milliliter, for spraying over the whole tree. Spray once every 7 days, for a total of 2 to 3 sprays. Because the aqueous solutions of the above pesticides easily lose effectiveness, especially streptomycin, it is best to prepare these pesticides immediately before use.