This blog will outline the reasons for fruit drop in citrus fruits and the most effective ways to prevent them.

Citrus farming has benefited farmers since it has a better economic yield than other fruit crops. Citrus fruits have risen to the top spot in terms of output and production area. However, a significant issue with citrus fruits is the substantial shedding of flowers and fruits from the flowering stage until harvest time.

Citrus trees often bloom lavishly in the spring, but only a small percentage of those flowers develop into fruit that remains on the tree and matures until harvest. For instance, less than 1% of flowers in Kinnow develop into fruit that may be harvested. The exact ratio of flowers to fruit that can be harvested varies yearly. Years with high flowering produce a lower proportion of flowers to fruit than years with lighter bloom.

Fruit loss at various growth and development phases can cause a low fruit-producing flower percentage. Fruits do not all fall at once; instead, they do so at multiple intervals. Extensive falling happens in more or less defined phases or times.

Table of contents:

1. Waves of Fruit drop
2. Physiological fruit drop 
3. Pathological fruit drop
4. Entomological fruit drop
5. Management

Waves of Fruit drop

The loss happens in waves at varying times depending on the citrus fruit type. Citrus trees shed their flowers and fruits in roughly three separate waves: the post-bloom drop, the June drop, and the pre-harvest drop.

Post-bloom drop (First wave):

This fruit drop begins shortly after flowering and results in the fall of incredibly small fruits. The farmer doesn’t give much thought to this decrease because it results from natural overproduction. This fruit drop caused the tree’s extra fruit burden to be reduced.

Summer or June drop (Second wave):

This fruit drop wave starts roughly one to two months after bloom; early developing fruit is abscised from trees with excessive fruit set in June, making up about 10% of the total fruits dropped. Fruits fallen at this time in Kinnow are roughly the size of marbles (about 1 to 2 cm in diameter). The fight among young fruit for energy (carbohydrates) for growth and development is the leading cause of the decline during this stage. Although citrus fruit drop in June is often seen as a natural occurrence during fruit growth, water shortage combined with high temperatures in the early summer can worsen fruit drop.

The third wave (comprise premature and pre-harvest fruit drop)

The third wave is the falling of almost mature to harvestable fruits, which includes premature and pre-harvest fruit drop. Pre-harvest fruit drop begins in August and lasts all the way through harvest. Fruit falls off without the peduncle attached when there is a drop at the peduncle and calyx junction.

This decline is significant economically for the farmer since it results in the loss of nearly fully grown fruits, which results in substantial losses for the grower. The majority of fruit drops prematurely as a result of disease transmission and fruit fly infestation. While low temperatures and foggy conditions in December and January are to blame for pre-harvest fruit loss.

Fruit Drop classification:

Several factors contribute to fruit drop in citrus trees. The fruit drops are classified into different categories based on these factors:

1. Physiological fruit drop 
2. Pathological fruit drop
3. Entomological fruit drop

Physiological fruit drop

Abscission is the term for the physiological process that causes fruit to fall. Plants subjected to physiological or environmental stress generally experience a physiological drop.

Physiological fruit decline is primarily caused by the following:

• Water pressure
• Extreme temperature
• Nutritional deficiency
• Prolonged periods of frost
• Tree in poor health

Pathological Fruit Drop 

Pathological fruit drop is a significant obstacle that lowers the output and quality of harvested produce. The premature fruits that fall during this fruit drop cause the growers to experience agony. Such fruits are no longer suitable for marketing. This decline has significant economic implications and, if unchecked, may significantly lower yield and returns.

As a result, adopting integrated strategies is essential for managing fruit drop effectively and sustainably. Pathological fruit decline often begins in August and lasts into harvest. The fall is most severe between September and October when the fruits are nearing maturity and have taken nutrients from the tree. Different plant pathogens, including Colletotrichum gloeosporioides, Diplodia natalensis, and Alternaria citri, are responsible for pathological fruit drop.

Entomological Fruit drop

Orange bugs and citrus bud mites are two significant pests that seriously reduce oranges’ ability to produce blossoms and fruits. Fruit drop is mainly caused by fruit flies (Daucus dorsalis) and fruit-sucking moths (Otherisfullonica) at the final, critical stage of fruit ripening. Fruit fly infection is the leading cause of fruit drop before harvest. It begins to be active in the final week of October and keeps going until the last harvest.

Management

How to stop or manage this kind of fruit drop is the question that now needs to be answered. Effective management strategies are crucial since they are required to preserve fruit quality and achieve increased yield. The following list includes management techniques for these fruit drops.

Management for Physiological Fruit drop

• It is crucial to keep trees healthy and protect them from stressful situations like too much or too little moisture, leaf yellowing caused by nutrient shortages, and the prompt elimination of diseases and insect pests.
• The citrus trees require the correct ratio of macronutrients and micronutrients to produce enough foliage to sustain the developing fruits. Apply suggested fertilisers accordingly to keep the plants growing healthily and vigorously. In order to prevent water stagnation, proper drainage arrangements must be made.
• During fruiting, citrus trees shouldn’t experience water stress because it speeds up the production of abscisic acid, which causes fruits to fall off more quickly.

Management for Pathological Fruit drop

Citrus pathological fruit drop can be controlled by implementing the following integrated management strategies:

• Citrus trees should be pruned to eliminate any twigs that are dead, diseased, decaying, or in danger of injuring other branches. In order to lessen the primary source of inoculum, citrus trees should be pruned in the months of January and February following fruit harvest.
• After pruning, Bordeaux mixture (2:2:250) or copper oxychloride 50 WP (3 g/liter of water) should be sprayed on the plant. Spray once again during the months of March, July, and September to lessen twig dieback.
• Avoid piling up pruned wood close to the orchard since it can spread disease. The pruned wood should all be gathered and burned to make it unusable.

Management for Entomological Fruit drop

• It has been demonstrated that clean culture, orchard sanitation, or removal and destruction of the fruit fly-infested fruits by burning or deep burying and ploughing around the trees are effective methods for controlling fruit flies.
• Fallen fruits must be properly disposed of because they draw moths to their habitat.
• Never leave fallen fruits out in the open. These fruits serve as a fruit fly nesting ground and a source of disease inoculum.

How can Fasal assist?

• Citrus fruit drop is a severe disorder that lowers fruit quality and yield. A single component does not just cause fruit drop; it is also influenced by several physiological factors, such as high humidity, extreme heat, and water stress, as well as a number of pathological and entomological causes, such as the spread of pathogens and pests. They are primarily responsible for citrus fruit losses.
• Fasal is a horticulture crop-focused AI system. It analyses temperature, humidity, the anticipated temperature at the canopy level, and a microclimate prediction favourable for fruit drop using its sensors.
• With the assistance of Fasal technology, you may use weather forecasts specific to farms to organise citrus production activities better.
• The Fasal System also provides early warning of pest and disease outbreaks, which significantly lowers the probability of fruit drop.
• Farmers can obtain a precise measurement of irrigation to be applied to the citrus crop using the Fasal system.
• The Fasal system suggests a pesticide dose for farms, ultimately lowering their pesticide costs.