Effective Pre-harvest Treatments for Fruits and Vegetables

The quality and shelf life of fruits and vegetables don’t depend solely on what happens after harvest. In fact, a significant portion of post-harvest performance is determined by treatments applied while the crop is still growing in the field. Pre-harvest treatments – the strategic use of specific chemicals and growth regulators before picking – can strengthen cell walls, delay ripening, prevent physiological disorders, and ultimately ensure that produce stays fresh much longer after it reaches the market. For farmers, exporters, and consumers alike, understanding these treatments is essential to reducing food waste and improving produce quality.

What are pre-harvest treatments? 🔗

Pre-harvest treatments refer to the application of chemicals, plant growth regulators, and nutrient sprays to fruits and vegetables while they are still on the plant, typically during critical stages like flowering, fruit development, or just before harvest. The goal is to modify the physiology of the produce so that it performs better after being picked – maintaining firmness, colour, taste, and nutritional value for a longer duration.

These treatments are considered proactive measures. Rather than waiting for post-harvest problems to appear and then trying to fix them, pre-harvest treatments address issues at their source. Research published in Frontiers in Plant Science highlights that the pre-harvest growth and development period is critical for forming the quality and disease resistance of horticultural crops, and that many pathogens remain dormant during this stage. Environmental factors like light, temperature, rainfall, and soil conditions – alongside cultural practices such as fertilisation, irrigation, and chemical sprays – all influence how well produce holds up after harvest.

Why pre-harvest treatments matter 🔗

Globally, an estimated 25-50% of fruits and vegetables are lost between the farm and the consumer. That’s a staggering amount of waste, especially when global food demand is expected to rise by 60% by 2050 to feed over 9 billion people. Pre-harvest treatments directly address several causes of these losses:

Preventing physiological disorders: Conditions like blossom-end rot in tomatoes and bitter pit in apples are directly linked to calcium deficiency during fruit development. Pre-harvest calcium sprays prevent these disorders before they occur.

Delaying ripening: Ethylene, a natural plant hormone, accelerates ripening and senescence. Pre-harvest application of ethylene inhibitors can slow down this process, giving farmers a wider harvest window and extending the produce’s marketable period.

Improving fruit firmness and storage life: Treatments that strengthen cell walls result in fruits that withstand transport, handling, and storage far better than untreated produce.

Reducing post-harvest chemical dependency: When produce enters the supply chain in better condition thanks to pre-harvest treatments, there is less need for aggressive post-harvest interventions like heavy fungicide applications or controlled atmosphere storage.

Key chemicals used in pre-harvest treatments 🔗

Calcium nitrate 🔗

Calcium nitrate is one of the most widely used pre-harvest chemicals for improving fruit and vegetable quality. It delivers two essential nutrients – calcium and nitrogen – both of which play critical roles in plant health and produce quality.

Calcium is vital for building strong cell walls. When plants receive adequate calcium during fruit development, the resulting produce is firmer and more resistant to physical damage during transport and storage. Calcium nitrate is the only fully water-soluble source of calcium available for plants, making it highly effective for foliar sprays and fertigation systems.

The most common disorders prevented by calcium nitrate include:

Blossom-end rot in tomatoes and peppers: This condition appears as sunken, leathery patches on the bottom of fruit and is directly caused by insufficient calcium availability. Foliar spraying of calcium nitrate during flowering and fruiting stages ensures adequate calcium reaches the developing fruit.

Bitter pit and cork spot in apples: Both conditions create discoloured depressions on the fruit surface and, in the case of bitter pit, affect taste as well. Pre-harvest calcium sprays applied at regular intervals during the growing season can significantly reduce these disorders.

Tip burn in lettuce: Calcium deficiency causes browning and death of leaf edges, which reduces marketability of leafy greens.

Application schedule for calcium nitrate 🔗

The timing and method of application are critical for calcium nitrate to be effective. According to Yara, a global crop nutrition company, calcium should be supplied continuously throughout the growth period because it has low mobility within the plant – once deposited in older tissues, it cannot be redistributed to new growth areas.

For foliar sprays, the typical recommendation is to dissolve 5-10 grams of calcium nitrate per litre of water and apply it 2-3 times during the crop cycle at intervals of 10-15 days, starting from the pre-flowering stage through fruit formation. In tomatoes, applications during the flowering and early fruiting stages are particularly important. For apple orchards, repeated cover sprays every alternate week until 2-3 weeks before harvest help prevent bitter pit and improve storage quality.

Calcium nitrate can also be delivered through fertigation (applying it via irrigation systems), which ensures a steady supply of calcium to the root zone. For soil-based application in vegetables, rates of around 150-200 lbs per acre at transplanting, followed by regular fertigation, are commonly recommended.

Ethylene inhibitors 🔗

Ethylene is a gaseous plant hormone that triggers ripening, softening, colour changes, and eventually senescence in fruits and vegetables. While ethylene is essential for natural ripening, uncontrolled ethylene activity leads to premature softening, over-ripening during transport, and accelerated spoilage. Ethylene inhibitors are chemicals that block or reduce ethylene’s effects, and their pre-harvest application has become an important tool in modern horticulture.

1-Methylcyclopropene (1-MCP) 🔗

1-MCP is the most commercially significant ethylene inhibitor used today. It works by binding to ethylene receptors in plant cells, effectively blocking ethylene from triggering the ripening cascade. Importantly, 1-MCP does not stop ethylene production – it prevents the plant from responding to it. This mechanism makes it highly effective even at very low concentrations.

While 1-MCP was originally developed as a post-harvest fumigation treatment, a sprayable pre-harvest formulation (marketed as Harvista™) has been developed for field application. A 2024 study on ‘Scilate’ apples found that a single pre-harvest 1-MCP spray applied one week before harvest resulted in higher malic acid content and lower juice pH after 7.5 months of cold storage. Treated fruit showed only 2% softening compared to 13% in untreated fruit, and respiration rates dropped by 32%.

Pre-harvest 1-MCP is particularly effective in apples, where it delays fruit drop, maintains flesh firmness, and reduces the development of storage disorders like flesh browning. It is also used in pears, mangoes, bananas, kiwifruit, and tomatoes.

Silver thiosulfate (STS) 🔗

Silver thiosulfate is another ethylene inhibitor, though it functions differently from 1-MCP. STS contains silver ions that interfere with ethylene perception at the receptor level. It is commonly applied as a foliar spray or dip treatment and is especially popular in floriculture for extending the vase life of cut flowers. In fruit and vegetable production, STS is used to delay ripening and reduce ethylene-driven senescence in specific crops.

Aminoethoxyvinylglycine (AVG) 🔗

AVG works by inhibiting ethylene biosynthesis rather than its perception. It blocks the enzyme ACC synthase, which is essential for producing ethylene in the plant. Pre-harvest AVG sprays are widely used in apple orchards to reduce pre-harvest fruit drop and extend the harvest window, giving growers more flexibility in scheduling their picking operations.

Growth regulators in pre-harvest management 🔗

Gibberellic acid (GA3) 🔗

Gibberellic acid is a naturally occurring plant hormone belonging to the gibberellin family. As documented by the USDA, GA3 is most commonly used on grapes, citrus, and apples, but also finds application in pears, strawberries, blueberries, lettuce, artichokes, and potatoes. Its uses include increasing fruit size, delaying or accelerating maturity, improving fruit appearance, and reducing fruit drop.

In grapes, GA3 is applied at the bloom stage to promote cell elongation, resulting in larger, more uniform berries. In citrus, pre-harvest GA3 sprays delay rind senescence – keeping the peel thick, firm, and green – without affecting internal fruit maturity. This allows farmers to delay harvesting until the fruit reaches optimal size and juice content. A systematic review published in PLOS ONE confirmed that pre-harvest GA3 applications can delay senescence in grapefruit and reduce the incidence of fruit disorders like creasing in oranges.

In kumquat, a study found that pre-harvest GA3 spraying at 20 mg/L maintained higher levels of beneficial hormones and reduced abscisic acid content, preserving fruit quality and extending post-harvest life.

Auxins 🔗

Auxins are plant hormones that regulate cell growth and fruit development. Synthetic auxins like naphthaleneacetic acid (NAA) are applied pre-harvest to reduce fruit drop in crops such as tomatoes, apples, and strawberries. By improving fruit retention on the plant, auxins allow more produce to reach optimal maturity before harvest, directly improving yield and quality.

Application schedules for common fruits and vegetables 🔗

Getting the timing right is just as important as choosing the correct chemical. Here is a practical overview of recommended application schedules for major crops:

Tomatoes: Apply calcium nitrate as a foliar spray during the flowering and early fruiting stages to prevent blossom-end rot. Use a 1-2% calcium nitrate solution every two weeks. AVG or 1-MCP sprays near harvest can delay ripening during transport.

Apples: Begin calcium nitrate sprays early in fruit development, repeating every 10-15 days through the growing season. Apply 1-MCP (Harvista™) as a foliar spray 1-4 weeks before anticipated harvest to maintain firmness and reduce storage disorders. AVG can be applied 4 weeks before harvest to reduce pre-harvest fruit drop.

Grapes: Apply GA3 at the bloom stage (70-80% capfall) for berry enlargement and cluster loosening. A second application may follow 5-7 days later. Calcium sprays during fruit development improve berry firmness.

Citrus (oranges, grapefruit, mandarins): Apply GA3 sprays during the colour-break period to delay rind senescence without affecting internal maturity. Research from the University of Florida found that GA3 treatment in citrus increased average fruit size by 5% and reduced pre-harvest fruit drop by 15-20%. Calcium sprays during fruit development reduce albedo breakdown in navel oranges.

Bananas: Post-harvest 1-MCP fumigation is the standard approach, but pre-harvest practices such as optimising harvest maturity and reducing mechanical damage during cutting are equally critical.

Peppers and cucumbers: Apply calcium nitrate through fertigation during fruit development to prevent calcium deficiency disorders. Foliar sprays at two-week intervals supplement root uptake.

Benefits of implementing pre-harvest treatments 🔗

The advantages of a well-planned pre-harvest treatment programme extend throughout the supply chain:

Higher quality produce: Treated fruits and vegetables have better colour, firmer texture, and improved taste due to optimised nutrient levels and delayed senescence.

Extended shelf life: By slowing ripening and strengthening cell structure, pre-harvest treatments can add days to weeks of marketable life. For example, 1-MCP-treated apples maintained quality through 7.5 months of cold storage in controlled studies.

Lower post-harvest losses: With new technologies continually emerging in post-harvest science, combining strong pre-harvest practices with advanced storage techniques (like nanotechnology-based antimicrobials and smart packaging) offers the most effective strategy for reducing waste.

Better market returns: Produce that arrives at market in superior condition commands higher prices. Firmer, blemish-free fruits with extended shelf life are preferred by both retailers and consumers, translating directly into improved profitability for growers.

Precautions and best practices 🔗

While pre-harvest treatments offer significant benefits, their success depends on proper application. A few important considerations include:

Follow recommended concentrations: Over-application of growth regulators like GA3 can lead to unintended effects such as reduced flavonoid and carotenoid content in citrus juice or delayed ripening that makes fruit unmarketable. Always adhere to label recommendations and local agricultural guidelines.

Timing is critical: Applying chemicals at the wrong growth stage reduces effectiveness or can cause harm. For example, calcium nitrate sprayed too late in the season may not reach the developing fruit adequately due to the low mobility of calcium within the plant.

Consider compatibility: Calcium nitrate is compatible with most insecticides and fungicides but should not be combined with sulphate-based products. Similarly, GA3 sprays on citrus should be kept at least 4 weeks apart from any oil-based spray applications to avoid phytotoxicity.

Environmental conditions matter: Foliar sprays should be applied during the early morning or late afternoon to avoid leaf burn from direct sunlight. Adequate soil moisture at the time of application improves nutrient uptake.

What do you think? Given the significant losses in the global fruit and vegetable supply chain, should pre-harvest chemical treatments be considered a standard part of every grower’s crop management plan? How can small-scale farmers in developing regions gain better access to these technologies?

References

1. https://www.frontiersin.org/research-topics/41458/preharvest-and-postharvest-factors-affecting-fruit-and-vegetables-quality-physiology-and-shelf-life/magazine
2. https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2023.1149358/full
3. https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/calcium-nitrate-fertilizer.htm
4. https://www.trees.com/gardening-and-landscaping/calcium-nitrate-fertilizer
5. https://www.yara.us/crop-nutrition/fertilizer-products/yaraliva/
6. https://www.intechopen.com/chapters/85574
7. https://link.springer.com/article/10.1007/s13580-024-00616-4
8. https://www.ams.usda.gov/sites/default/files/media/Gibberellic%20Acid%202%20TR.pdf
9. https://pmc.ncbi.nlm.nih.gov/articles/PMC6762134/
10. https://edis.ifas.ufl.edu/publication/HS1456
11. https://pmc.ncbi.nlm.nih.gov/articles/PMC10178206/