Latest Technical Measures for Flower and Fruit Thinning in Citrus

Although there are many types of citrus, most of them share the characteristic of producing many flowers and many fruits. Citrus often blooms all over the tree during the flowering period, but flowers keep dropping throughout the entire flowering period, and only one third of the flowers eventually set fruit. The number of fruits that citrus sets is also relatively high compared with other fruit trees, but the number that finally holds firmly decreases further. At this point, if no one comes to select flowers and thin flowers, or select fruits and thin fruits, and it is left to natural selection, the losses may be greater.

I. Purpose of Flower and Fruit Thinning

Citrus blooms profusely, but not all flowers can become fruit. 90% of the flowers will drop with physiological flower and fruit drop, which consumes a large amount of tree nutrients and weakens tree vigor. Therefore, most of the flowers should be thinned out, leaving the best flowers in the best positions to set fruit. After fruit set, only the fruits on fruiting branches with clearly stable fruit set should be retained, and fewer fruits should be kept on weak branches, in order to concentrate nutrients and maximize their use in useful parts.

II. Flower and Fruit Thinning

1. Manual flower thinning

Flower thinning can be carried out throughout the entire flowering period, but it is still best to do it as early as possible. The earlier it is done, the less is consumed; on the contrary, the more is consumed. Generally, fruiting branches borne on slender weak branches, defoliated branches, and basal branches are thinned away together with their flowers and branches. Flowers on late autumn shoots or on shoots whose leaf color never turns green may be abnormal and need to be cut back, retaining a portion of potentially effective flowers, or they may all be removed. If multiple flower buds are borne in the leaf axils of the same flowering and fruiting branch, only two good flower buds need to be retained, and the rest should be removed. In addition to these, all weak flowers, incomplete flowers, flowers damaged by pests and diseases, poorly developed flowers, excessively dense branches, and vigorous water shoots should be removed.

2. Manual fruit thinning

At the early stage of fruit set, you can first shake the tree. Fruits that fall off with a gentle shake are all fruits that cannot hold. Then diseased branches and diseased fruits should all be removed. In addition, retain 6 to 8 fruits on strong fruiting branches, retain 5 to 6 fruits on slightly weaker fruiting branches, and thin out the rest. Fruits that are too densely clustered in the same space should have some removed.

3. Chemical flower thinning

In regions and varieties that flower early, naphthaleneacetic acid can generally be sprayed about 20 days after full bloom to thin flowers, but for varieties that flower late, spraying can begin one month after full bloom, relatively delayed. After spraying, weak flowers drop off automatically.

4. Chemical fruit thinning

Manual thinning consumes a lot of labor and has higher costs, so growth regulators can be used to thin flowers and fruits. Generally, ethylene accelerates abscission layer formation and has a fruit-dropping effect, so indole ester can be sprayed to increase the ethylene content in the tree to thin fruits. Ethephon can also be used; the amount of ethylene produced is greater than that of indole ester, but the duration is shorter.

The reason for thinning flowers is to better preserve flowers, then concentrate high-quality flowers to set fruit and reduce consumption. Likewise, thinning fruits is also to concentrate nutrients for high-quality fruits, preserve fruits, and improve yield and fruit quality. Therefore, flower and fruit thinning should be viewed correctly. Do not feel regretful about it, and avoid alternate bearing.