A Detailed Guide to May Citrus Fruit Retention Methods and Precautions

From early to mid-May through the end of May is the critical period for stabilizing citrus fruit set. In citrus production, this period is commonly called the fruit retention period - fruit stabilization period. At this time, it is the key period that determines yield. So what May citrus fruit retention methods are there? What aspects need attention?

1. What May citrus fruit retention methods are there

The key to fruit retention lies in balancing tree nutrition, maintaining a reasonable leaf-to-fruit ratio, increasing the carbohydrate content in the tree, raising the carbon-to-nitrogen ratio, reducing the conflict between shoots and fruit, and prompting more organic nutrients to be supplied to the young fruit for growth and development.

1. Nutrient supplementation

Because flowering consumes a large amount of nutrients, after petal fall is a period when elements such as nitrogen, phosphorus, potassium, calcium, magnesium, and boron are deficient, especially nitrogen, boron, and zinc. Timely supplementation is beneficial for fruit retention.

Citrus bud drop and flower drop consume the most nitrogen from the tree, so nitrogen fertilizer should be properly top-dressed during the flowering period, such as high-nitrogen water-soluble fertilizer, 1-2 kg per mu. For citrus trees with too much fruit, too few branches and shoots, and average tree vigor, 2-3 kg of water-soluble organic fertilizer per mu should be applied to nourish the roots. From April to June is the young fruit expansion period of citrus. At this stage, nutrient demand is high, and 1-2 liang of potassium fertilizer should be top-dressed per tree.

2. Hormone regulation

Fruit trees in the flowering and young fruit stages secrete large amounts of auxin, abscisic acid, and other substances. However, if these substances are secreted in excess, they can cause nutrient excess and lead to heavy fruit drop. Therefore, timely and reasonable supplementation of hormones such as gibberellin can increase the fruit-setting rate. But the timing of using hormones for fruit retention must be correctly grasped. If gibberellin is sprayed too early when there are many shoots and few flowers or before petal fall, it is easy to enlarge leaves and cause excessive new shoot growth, which is not conducive to fruit retention. Late-maturing citrus types are mostly seedless and few-seeded citrus varieties and can be used earlier, sprayed when 2/3 of the petals have fallen. For multi-seeded varieties or pomelo types, use gibberellin sparingly or not at all.

During the fruit retention period, using natural regulators such as seaweed extract, brassinolide, and sodium nitrophenolate can enhance the tree's stress resistance and regulate the transfer and transport of plant nutrients from branches and leaves to flowers and fruit, avoiding blocked fruit growth caused by excessive vegetative growth of branches and leaves.

3. Physical girdling

Girdling is also an important method of fruit retention. Choose vigorous trees for girdling. If the tree is weak or is a young tree, girdling is generally not needed; otherwise it will weaken the tree, affect the sprouting of autumn shoots, reduce yield, and in severe cases cause yellowing and tree death.

For spring girdling for fruit retention, after petal fall and within 7-15 days after spraying gibberellin plus foliar fertilizer, when spring shoot leaves are 90% turned green and very few new buds are sprouting, is the most ideal time to cut. Too early affects the tree turning green and the fruit-setting amount; too late, once shoots emerge, it is difficult to control them.

Seedless varieties are not easy to retain fruit and basically all require girdling to achieve high yield. For seeded varieties, it depends on the rootstock and tree vigor. For Mashuiju, Wogan, and others, it depends on the rootstock and the number of flowers. If it is a strong rootstock such as sour orange rootstock, with many flowers and vigorous trees, girdling is recommended. In addition, first-fruiting trees are often not easy to retain fruit, and girdling can be considered for fruit retention when abnormal weather occurs.

2. What issues should be noted during fruit retention

1. Fertilizer spraying

Every 1,000 citrus flowers consume 2 grams of pure nitrogen. When citrus blooms heavily, it consumes more nutrients, and if fertilizer is not supplemented, it is very difficult to stabilize fruit. During the young fruit period, about 3 liang of urea can be supplemented per tree. For trees with especially weak vigor, supplementation is still needed in June.

2. Shoot removal

Citrus bud emergence and flowering and spring shoot sprouting, as well as young fruit growth and shoot sprouting, all proceed at the same time, competing with each other for organic nutrients. If too many shoots sprout, flowers and fruit will drop. Therefore, for young trees bearing fruit for the first time, especially vigorously growing trees, some strong spring shoots and all June shoots should be removed.

May is an important period that determines the yield of citrus trees. Only by carefully doing the best fruit retention work can fruit yield and quality be improved.