Navel Orange and Citrus Canker: Symptom Identification, Control Methods and Pesticide Preparation

High temperature and frequent rain, high humidity and high temperatures: this kind of weather is extremely favorable for the occurrence of navel orange and citrus canker. Canker mainly damages the young shoots, young leaves and young fruit of navel orange. So what are the control methods for navel orange and citrus canker? How is the pesticide prepared?

1. Canker symptoms

Canker is a disease caused by bacterial infection. It can damage navel orange leaves, fruit and shoots. In the early stage of the disease, small yellow or yellow-green water-soaked spots appear; after they expand, they form nearly round, raised lesions with a sunken center and a yellow halo around them. In severe cases, it causes a large amount of leaf drop, fruit drop and shoot dieback. It seriously affects the yield and quality of the fruit trees.

Leaf damage

At first, yellow or dark yellow-green oil-soaked round spots the size of a needle head appear on the underside of the leaves. After they expand, they gradually become raised on both the upper and lower sides of the leaf, becoming nearly round, cream-yellow lesions.

Soon, the center of the diseased part ruptures, the raised area becomes more prominent, the surface is rough, lignified, and grayish-white or grayish-brown in a crater-like shape. The diseased part is mostly round, often with concentric rings or spiral patterns, surrounded by a yellow or yellow-green halo ring, and close to the halo ring there is often a brown glazed edge.

Sometimes several lesions merge with each other, forming irregular large lesions. In the later stage, the center of the lesion sinks and cracks open in a crater-like shape.

Shoot damage

The characteristics of the lesions are basically similar to those on the leaves. At first, small oil-soaked round dots appear, dark green or wax-yellow; after expanding, they become grayish-brown, lignified, and more raised than the lesions on the leaves.

The center of the lesion sinks and cracks open like a crater, but there is no yellow halo ring. In severe cases, it causes leaf drop and shoot dieback, with summer shoots being especially serious.

Fruit damage

The lesions on the fruit are also similar to those on the leaves, but the lesions are larger. The degree of lignification is even greater than that of leaf lesions, and they are firmer. The crater-like cracking in the center of the lesion is also more prominent. In some citrus varieties, there is a dark brown glazed edge at the boundary between the diseased and healthy parts.

Due to differences among varieties, the width of the glazed edge varies. The lesions are limited to the rind, and in severe cases they cause early fruit drop.

2. Conditions for occurrence

1. Climatic conditions

High temperature and frequent rain (May-September each year) are necessary conditions for the epidemic of the disease. The disease can occur when the temperature is above 15°C, but 20-36°C is more suitable, and 25-30°C is the most suitable. Rainwater is the main medium for the spread of the pathogen. Therefore, when the temperature is suitable, rainfall and rainy days are positively correlated with the epidemic of the disease. Rainfall also affects the size of the lesions. Generally, in the spring shoot period, the temperature is low and rainfall is low, so the lesions are smaller; in the summer and autumn shoot periods, with high temperature and frequent rain, the lesions are larger.

2. Growth stage

The canker pathogen generally only infects young and tender tissues at a certain stage of development. It does not infect, or rarely infects, newly emerged young shoots, young leaves, young fruit just after flowering, and mature tissues. This is because the stomata of very young tender tissues have not yet formed, so the pathogen cannot invade. In mature tissues, most of the original stomata are aged, and the openings are extremely small or closed, making it difficult for the pathogen to invade.

3. Cultivation management

Unreasonable fertilization prolongs the shoot emergence period, increases the number and quantity of shoot flushes, and delays maturity, which favors pathogen infection; excessive application of nitrogen fertilizer promotes disease occurrence, while increasing potassium fertilizer can reduce disease occurrence. If diseased branches are not pruned in winter, the disease will be more severe the following year; removing summer shoots and controlling autumn shoots can significantly reduce disease occurrence. In orchards with severe damage from pests such as citrus leafminer, citris leaf beetle and swallowtail butterflies, canker often occurs more seriously.

4. Tree age

Seedlings and young trees are more susceptible to the disease, and the older the tree, the milder the disease. This is because seedlings and young trees have more summer and autumn shoots and more shoot flushes, which favors pathogen invasion.

3. Control measures

1. Clean the orchard and remove leaves

Clean the orchard in winter, collect fallen leaves, fallen fruit and dead branches, and burn them. In early spring, combine pruning to remove diseased and pest-infested branches, diseased leaves, leggy branches, weak branches, etc., so as to reduce the sources of disease infection. Starting from the seedling stage, remove diseased leaves, especially after typhoon rain, and prune severely diseased shoots.

2. Fertilizer and water management

Reasonable fertilizer and water management should be used to cultivate uniform spring and autumn shoots and control the growth of summer shoots. At the same time, during each shoot emergence period, timely control of citrus leafminer should be carried out.

3. Scientific selection of pesticides

Main formula: 100 jin of water, 0.5 jin of copper sulfate, 1 jin of ammonium bicarbonate, 1 jin of lime. Preparation method: first dissolve the copper sulfate, prepare a 90% copper sulfate solution, then add the ammonium bicarbonate aqueous solution, then dissolve the lime in 10% water and remove the residue (preferably use lump lime), and finally slowly pour the ammonium bicarbonate and copper sulfate mixed solution from low to high into the lime water solution, and it is ready.

4. How to use

Spray the prepared copper-ammonium-lime mixture directly without dilution. If there are aphids, add 5% abamectin 800-1000 times solution for spraying. This mixture causes slight phytotoxicity to young leaves and shoots, but does not affect shoot growth, so it can be used boldly. It does not cause contamination of fruit; there may be contamination at first, but it can be washed off by rain.