Flushing constitutes an important maintenance routine. In micro-irrigation systems provisions must be made to flush mains, submains and lateral lines to remove settled sediments.

Mainline should be flushed at scour valve locations, whilst submains are flushed at slushing points usually located at the ends of the lines while the system is running and allow water to run into a container until it runs clear. Collect some of the dirty water in a glass or clear plastic container and examine the contaminants. Take note of the nature of the impurities in the water. If there be significant amount of contaminant in the flush water, find out what it is. Does it appear to be bacterial slime? Are large aggregated particles present? Is there evidence of iron precipitation? Is there any material that could be sand from the media filter?

If unsure, have water examined and take corrective action to cure the problem. If chlorine or acid treatment is required follow the steps below for treatment.

Please note whenever a repair has been carried out on any pipe work in the system, flushing and cleaning of filtration will have to be carried out.

At the end of the season empty mainlines, field filters and valves and ensure all ball valves are opened to drain the water from within the ball and then shut again to prevent vermin and contaminants entering the system. This draining of components will help in preventing frost damage.

Chlorinating the System

The most common chlorine compounds are sodium hypochlorite (liquid) and calcium hypochlorite (solid). Sodium hypochlorite (10% chlorine) is easier to use and relatively safe.

There are four main chlorine application methods:-

• intermittent treatment 
  
• continuous treatment
• superchlorination
  
• end of season chlorination
  

The procedures below should be used as a guide to developing a procedure that suits your system, water conditions and management.

Intermittent treatment involves periodic sterilisation by chlorination and can also be used to prevent build-up of organic matter in the system. This is the most commonly used preventative treatment. 30 ppm chlorine is injected 3 - 4 times during the season.

Continuous Treatment uses a constant injection rate, usually of 5 to10 ppm, adjusted so that 1 ppm of chlorine is detectable at the end of the furthest lateral from the pump. A swimming pool tests kit can be used to detect chlorine and its level.

• Irrigation
• Nutrition
• Pruning
• Pest and Disease Control

Irrigation

"A grove without an effective irrigation system is unlikely to deliver consistent yields year after year. Many growers still underestimate the water needs of olive trees, and few actually monitor soil moisture levels. This is why so many groves have never achieved a commercial crop."  Marcelo Berlanda Specialist Olive Consultant

Water stress negatively affects flowering, fruit set, oil accumulation (oil production), fruit size (table olives), fruit quality, and overall tree health. However, many growers lack a proper system to monitor soil moisture or manage irrigation effectively. 

Marcelo recommends:

"Growers should inspect soil moisture weekly during spring and summer, and every two weeks in autumn and winter. Use a shovel to dig at least 400mm under the tree canopy to check moisture. If the soil is hard to dig, it’s too dry – even if the canopy shows no visible signs of stress." 

Advanced soil moisture monitoring tools can also provide reliable data on a digital display or computer dashboard. 

For optimal grove health, growers must consistently check soil moisture and prevent water stress.

Nutrition

As discussed previously, taking leaf samples is essential to assess your trees’ nutritional status. This information guides the creation of a fertiliser program, a critical component for boosting or maintaining yields.

Typically, no fertiliser is needed in winter, unless you’re addressing soil amendments. However, some groves have severe nutrient deficiencies requiring fertiliser even in winter. Where proper irrigation systems aren’t in place, growers must broadcast fertiliser before rain to allow rainfall to incorporate nutrients into the soil profile, an inefficient use of resources but often the only option.

When applying fertiliser in these conditions, target the area beneath the canopy and, if possible, cultivate the soil to improve incorporation and reduce product loss.

Olives need four essential nutrients: Nitrogen, Phosphorus, Potassium, and Calcium. Check product labels carefully. As a general guideline, aim for:

• Nitrogen 15%
• Phosphorus 5% or less
• Potassium 10% or less
  
• Calcium 2% or less
  

Pruning

Avoid pruning during the coldest part of winter and when it’s wet or foggy to reduce the risk of bacterial and fungal disease spread.

The main goals of pruning are to remove dead wood, reduce canopy size, restore tree balance, encourage healthy new growth, and increase fruit set in spring.

Tip: After pruning, apply a copper-based spray to protect wounds from infection by fungi and bacteria.

Pest and Disease Control

Pest & disease management is crucial for sustaining yield and tree health. Winter’s colder temperatures reduce insect activity, offering a prime time to tackle pest issues.

Set up a comprehensive Pest and Disease Monitoring Program. During winter, check marked trees (previously affected by pests or diseases) every two weeks; in spring, check weekly. Look under leaves and on new growth for signs like crawlers, yellow spots, black sooty mold, or anything unusual.

Proactive, weekly management is essential for a successful grove.

If you need further assistance, please contact us.

At the 5th International Conference on Sustainable Agriculture and Biosystems, researchers in Iran presented findings on why fruit and flower drop occurs in fruit trees and what growers can do to reduce losses. Drawing on their work, we explore the phenomenon of fruit and flower drop, the underlying causes, and practical remedies for orchard managers.    

The Role of Fruit Trees in Agriculture

Fruit trees contribute significantly to agricultural economies across the world. Their production supports farm income, provides employment for skilled horticulturists, and underpins industries ranging from fresh produce to processing and food manufacturing. Cultivation involves a complex mix of practices: careful irrigation management, balanced fertilisation, pruning, pest control, and the application of modern technologies. Beyond economics, fruit trees are valued for their nutritional contributions, supplying sugars, oils, proteins, vitamins, and essential minerals through both fresh consumption and processed goods.

The Phenomenon of Fruit and Flower Drop

Fruit and flower drop is a natural occurrence in many tree species. Its extent varies according to cultivar, climate, soil type, and orchard practices. In some cases, drop is beneficial, helping the tree regulate excessive fruit load through “natural thinning.” But when drop is excessive or occurs at the wrong stage, it becomes detrimental, reducing yields and profitability.

Researchers typically divide drop into three categories:

1. Natural Drop: This type results from competition between a very high number of flowers. Up to 90% of flowers and fruitlets may be shed in some species, but the remaining fruit usually develop adequately. Growers sometimes assist by thinning to ensure the fruit that remain receive sufficient nutrition and reach high quality.
2. Abnormal Drop: This type is more damaging because it affects flowers and fruits at various stages of development, including larger fruit, often reducing yields significantly.
   
3. Extreme Temperature Drop: This occurs during periods of hot, dry weather (often around June in many regions). While widespread, it usually has limited impact on the final crop load.

Causes of Abnormal Drop

Environmental Factors

• Extreme cold or heat events can damage blossoms or young fruit.
• Strong winds, particularly dust-laden storms, may strip flowers and fruit from trees.
  
• Heavy rainfall or hail can injure delicate blossoms.
  
• Excessive direct sunlight can cause sunburn, leading to premature fruit drop.
  

• High-pressure pesticide or nutrient spraying can dislodge flowers.
• Over-application or incorrect doses of sprays may also contribute to flower drop.
  

• Poor pollination and failed fertilisation result in flowers dropping.
• Over-competition for nutrients between flowers and developing fruit increases drop.
  
• Nutrient deficiencies, especially nitrogen and zinc, play a role.
  
• Irregular irrigation - including overwatering that suffocates roots - can trigger drop.
  
• Shallow soils limit root systems, reducing nutrient uptake and increasing drop.
  
• Weak or diseased leaves caused by pests, fungal infections, or poor tree health reduce a tree’s ability to support fruit.
  
• Misuse of plant growth regulators or tank mix errors in spraying can disrupt flowering.
  
• Infections of flowers or fruit by fungi or insects often lead to drop.
  
• Natural ripening and senescence also account for some degree of fruit shedding.
  

The Science Behind Fruit and Flower Drop

The underlying mechanism of drop is closely linked to plant hormones. As fruits grow, the concentration of auxins (growth-promoting hormones) declines, while ethylene levels rise. This shift lowers the fruit detachment force (FDF), weakening the connection between fruit and tree. The abscission zone (the separation layer) becomes increasingly sensitive to ethylene, causing fruit drop. Environmental conditions such as temperature and humidity interact with these hormonal signals to intensify drop.

Remedies to Reduce Fruit and Flower Drop

Growers can apply several strategies to reduce drop and improve fruit set:

• Fertilisation: Apply fertilisers well before flowering to build soil fertility. Nitrogen should be supplied before bloom, not after, to avoid negative effects.
• Micronutrient Sprays: Foliar applications of calcium, zinc, and boron—adjusted for tree age and timing - can enhance pollination and fruit retention.
  
• Pruning: Moderate winter pruning balances vegetative growth with fruit production.
  
• Girdling: In some fruit tree industries (e.g., apples and pears), carefully removing a ring of bark from branches at flowering can improve fruit set.
  
• Irrigation Management: Avoid excessive watering during bloom and fruit set to prevent root suffocation.
  
• Growth Regulators: The use of auxin-based products, such as seaweed extracts (rich in auxins, cytokinins, and gibberellins), can delay fruit drop and extend the flowering period.
  
• Pest and Disease Management: Prompt control of pests and fungal infections prevents cascading effects on fruit drop.
  
• Pollination Support: For self-incompatible varieties, ensure compatible cultivars or introduce pollinators like bees and butterflies.
  
• Windbreaks: Plant hedges or wind barriers to reduce wind damage and limit flower and fruit loss.

Practical Advice

While some degree of fruit and flower drop is unavoidable, excessive losses can usually be mitigated through careful orchard management. Attention to fertilisation, irrigation, pest control, and pollination provides the best defence against unnecessary drop.

Further Reading and References

• Concentrated Seagold Seaweed Extract
• Nitrogen Fertilisers
  
• Boron Application
  
• Calcium Fertilisers
  
• Zinc
  
• Soil Test & Leaf Analysis
  
• Pruning and Grafting tools
  
• Pruning machines 
  
• Gardening tools