Citrus Pests and Diseases Are Frequent in June: Causes of Massive Fruit Drop and Control Measures

As June approaches, with high temperatures and drought, citrus trees lack sufficient nutrients, and a large amount of fruit drop occurs, which makes farmers very anxious. It is still the summer shoot stage now, and the sprouting of summer shoots can cause severe fruit drop. Some farmers are eager to remove the shoots, and improper girdling can also cause fruit drop.

There are so many factors behind fruit drop. Let us analyze them in detail below.

What are the reasons for the current massive fruit drop in citrus?

A thousand orchards have a thousand situations. Different orchards differ greatly. There are management problems as well as pest and disease causes. Which one is it exactly? This still needs to be analyzed by the manager who knows their own orchard best, and then matched accordingly.

1. Management problems

1. Poor control of summer shoots

Overly vigorous summer shoots have a relatively large impact on flower and fruit drop. Summer shoots compete with young fruit for nutrients, and the fruit cannot outcompete the summer shoots. By the time fallen fruit covers the ground, the trend of fruit drop can no longer be controlled. Therefore, for citrus fruit retention, the second physiological fruit drop and summer shoot control are very important.

Everything has two sides. Some managers prevent summer shoots excessively and spray excessive shoot-killing agents or chlormequat, which can likewise cause massive fruit drop in citrus.

2. Improper girdling

For Shatangju mandarin that needs fruit retention, girdling has been proven to be the best method of fruit retention at present, but if the cut is too deep and the wound does not heal, it will cause massive fruit drop.

3. Nutrient imbalance

This is relatively common in fruit trees that are given excessive nitrogen fertilizer. Such fruit trees have luxuriant branches and shoots that compete with the fruit for nutrients. Once consecutive rainy days occur and light is insufficient, the nutrients initially stored in the tree cannot keep up, and massive fruit drop will occur.

In addition, long-term rain can also cause waterlogged roots, root hypoxia, and worsen fruit drop.

4. Magnesium deficiency in the tree

The greening of new shoots and leaves requires the participation of magnesium. When fruit trees are deficient in magnesium, shoots and leaves will compete with fruit for magnesium, manifesting as yellowing around the fruit stalk, followed by dropping. This is what we call yellow-stalk fruit drop.

5. Navel yellow fruit drop

In terms of variety, the navel yellow problem of navel orange will also continuously cause massive fruit drop. The high-temperature and drought weather from July to September is often accompanied by dry hot winds and strong light. The causes of navel yellow are relatively complex. If too much fruit is really dropping, drugs such as navel yellow inhibitors can be used to prevent navel yellow.

2. Pest and disease problems

1. Anthracnose and brown rot

In summer, during the hot and rainy season, the common diseases that cause massive fruit drop are anthracnose at the fruit stalk, that is, stalk-blight anthracnose, as well as brown rot, etc. These diseases easily cause fruit drop and easily occur in closed, water-accumulating orchards and poorly managed orchards.

2. Fruit-piercing noctuid moths and fruit flies

During the fruit expansion stage, pests such as fruit-piercing noctuid moths and fruit flies will also cause a certain amount of fruit drop.

General solutions

Different methods are used for different situations, but some general methods can be used.

1. Reduce the use of nitrogen fertilizer. A high-potassium foliar fertilizer can be applied, such as sugar alcohol chelated potassium, to promote maturity and improve the transfer of nutrients to the fruit. For severe fruit drop, diethyl aminoethyl hexanoate can be added to reduce abscisic acid formation in the fruit and further reduce fruit drop.

2. For vigorous Shatangju mandarin trees after girdling, another cut can be made after the wound heals, which can reduce fruit drop.

3. Drought resistance and mulching: keep grass to retain moisture and maintain temperature, or cover the orchard with straw to avoid heat damage causing fruit drop.

4. Supplement water appropriately. Although it is dry, the orchard should still be given water as much as possible, by manual watering and pumping through pipes, so that soil moisture remains at a certain level. For weaker fruit-bearing trees or young non-bearing trees, water-soluble flush fertilizer can be added for irrigation to supplement nutrients and improve plant stress resistance.

As June is about to begin, with temperatures rising in various places, the vast majority of pests on citrus have already begun to emerge and cause damage. So which pests should be paid most attention to in summer citrus management?