At present, citrus varieties are ripen and are about to enter the harvest season, but at this critical time, there is a headache for many fruit farmers - pre-harvest fruit drop. Today, let's analyze the causes of this problem in depth and discuss effective measures for prevention and remediation. First, let's explore the three main factors that contribute to fruit drop, and understand the causes in order to better remedy them.
1. Weather factors
Rainfall
Long-term drought leads to water stress, which affects calcium transport and absorption, and causes citrus cracking and shedding.
In the late stage of drought, the moisture of the fruit increases sharply, the pulp cells expand rapidly, and the pericarp cells expand slowly due to the limitation of the stratum corneum, which is easy to lead to cracking and falling off.
Continuous rainfall or flooding in the late stage of fruit expansion or coloring period will also cause a large number of citrus cracks and falls off.
The temperature drops
When the temperature drops, the cells on the fruit stalk begin to senesce when the fruit is ripe, forming a "delayer".
Low temperatures promote the formation of endogenous hormones, causing citrus to fall off early, resulting in reduced yields.
At low temperature, the absorption capacity of the root system is weakened, and the aboveground part is still growing, resulting in a nutrient gap, and the demand for fruit expansion is large in the later stage, but it cannot grab the top branches, resulting in the fruit stalk leaving the layer and falling the fruit.
2. Nutritional elements
The tree has poor strength and weak root system
Citrus trees with weak roots have limited root absorption capacity and a lack of organic matter resulting in a large number of fruit drops.
Autumn shoots are not ripe or have late hair extractions
Partial application of nitrogen fertilizer, low temperature and drought lead to the autumn shoots are not easy to mature and ripen, and the shoots compete with the fruit for nutrients, resulting in insufficient nutrients and a large number of fruit drops.
The amount of fruit hung is large
Nutrition is limited, and the amount of hanging fruit is too large, resulting in the fall of weak and small fruits.
Magnesium deficiency
Preharvest fruit drop in citrus is related to magnesium deficiency, which affects chlorophyll synthesis and reduces photosynthesis.
New shoots and new leaves need a lot of magnesium to turn green, and when magnesium is deficient, the shoots and leaves compete for magnesium in the fruit, and the peel turns yellow and falls off, which is the so-called "yellow pedicle falling fruit".
3. Pest and disease infestation
Anthracnose
After the fruit swells, a large amount of nutrients are consumed, which weakens the tree, and the bad weather is prone to spittle anthracnose, causing the fruit to fall off.
Phytophthora brown rot
It usually occurs after sustained rainfall, and susceptibility leads to a large amount of fruit drop.
Orange fruit fly
From September to November, the adult ovipositor pierces the fruit skin to lay eggs, and the larvae feed on the fruit, resulting in a large number of fruit drops.
Other insect pests that can cause fruit drop include Spodoptera exigua, peach borer, bugs, etc.
This is the main reason why citrus fruits fall before harvest. In the face of these causes, how should we prevent and remedy them?
1. Strengthen tree nutrition
Pay attention to the application of organic fertilizer, balance phosphorus, potassium and trace elements, promote the aging of autumn shoots, supplement fast-acting nutrients to fruits, and avoid nutrient competition.
For trees with weak strength and many fruits, timely fertilization outside the roots should be carried out.
Spraying Spano is abundant, accelerates the ripening of autumn shoots, enhances the nutrition of the tree, and promotes the color change of citrus. Note: Foliar fertilizer containing hormones should not be sprayed during the veraison period, so as not to drain the nutrients of weak trees and aggravate fruit drop.
2. Appropriate use of growth regulators
For fruit trees with serious fruit drop, when spraying phosphorus and potassium fertilizer on the foliar surface, growth regulators should be added appropriately to inhibit the production of plant endogenous hormones, reduce the fruit drop rate, enhance the stress resistance of citrus trees, and promote the physiological differentiation of flower buds.
III. Hanging Branches
For orchards with dense branches and drooping fruits, timely carry out means such as hanging branches, pulling branches, and supporting fruits to avoid fruits being blocked by branches and leaves, and prevent infection with germs in rainy days.
It can increase light transmittance and air permeability, improve photosynthetic efficiency, promote the later development of fruits, and prevent fruit drop caused by insufficient organic nutrients.
Fourth, the prevention and control of pests and diseases
Spray protective fungicides before the fruit veraison, before and after the rain or before the disease falls and the fruit falls early.
These measures can help fruit farmers effectively prevent and remedy the problem of preharvest fruit drop of citrus, and improve yield and fruit quality.