Organic mango production: strategies and methods

Going organic with mango production

To meet organic certification requirements, conversion from a conventional system to an organic system is likely to involve changes to existing management practices and adoption of some new strategies and techniques. Changes to management go beyond simply not using synthetic chemicals and fertilisers.

This article outlines some of the strategies and methods used by organic mango growers that should be considered when planning conversion of an existing conventional production system. Please note that details provided are general outlines only.  Specific techniques and strategies adopted by individual organic growers will vary according to their circumstances, location of the property and type of enterprise.

Good organic managers rely on close observation, anticipation and prevention to develop a robust and productive organic system tailored to their situation.

Overall management strategies need to reflect the following key organic farming principles:

• Soil health largely determines plant health.

• Organic systems are biological systems.

• Organic farms should operate as closed systems as far as possible.

• A holistic approach ensures good integration of management practices.

Many of the best management practices developed for conventional mango production apply to organic systems. Efficient irrigation, windbreaks, erosion control, and aspects of integrated pest management (IPM) or integrated weed management (IWM) may be adapted to suit an organic production system. Quality control management systems, preferably incorporating a HACCP (Hazard Analysis and Critical Control Point) system will assist.

As with other organic farming, mango production requires a whole-farm approach. Increased reliance on management rather than chemicals demands careful planning.

A well designed whole-farm plan should devote special attention to the conversion phase – the first three years of transition from conventional to organic management. During this period practical experience is being developed and market price premiums for ‘in conversion’ product may be less certain.

Mapping out the details of the progressive changes intended will help develop a smooth conversion towards a profitable, productive and sustainable organic system. Such a plan can enable financial risk to be managed and adoption of each new operational component of the organic system can be readily integrated with other farm activities to improve management and enterprise effectiveness.

The major changes relate to the following aspects of a conventional production system:

• soil fertility and nutrient management

• orchard floor management

• irrigation layout

• weed management

• flowering habit

• pest and disease management

• postharvest treatments.

No synthetic fertilisers

Managing nutrients is important because synthetic chemical fertilisers are not permitted. Many conventional growers wrongly believe organic systems use no fertilisers at all. In fact a wide (and increasing) range of nutrient inputs is permitted, making it possible to correct any soil imbalance and provide specific supplements as required.

The main difference from conventional systems is that inputs are used to manage soil fertility through biology. Growing plant cover over the orchard floor and mowing to create mulch fuels soil biological activity generating soil fertility and plant available nutrients.

Applying supplementary fertiliser inputs only becomes necessary when an imbalance or deficiency can be demonstrated. The amount of supplementary inputs diminishes over time to maintenance levels.

A number of growers also use the 'Albrecht' method of balancing soil chemistry. Dr William Albrecht was an American soil scientist who established a set of ideal ratios for the main soil cations (Ca, Mg, K, Na). This method stresses the importance of the Ca to Mg ratio as a key driver of soil and plant health. Various other alternative soil management approaches are briefly described in the attachment.

Mangoes are generally known to be sensitive to excess nitrogen during the fruit development and ripening stages. This can result in poor quality and green fruit with poor storage characteristics.

Calcium and potassium levels are also thought to influence fruit quality and storage.

Trace elements like zinc, copper, boron and manganese are important. The role of boron in flowering and internal fruit quality is especially important.

In general, nutrient supplements can be applied to remedy identified soil deficiencies - rather than applying as a routine event. Occasional foliar nutrients are permitted.

Soil and plant tissue tests are important to verify nutritional requirements. The general approach toward correcting any deficiency is via the soil, rather than applying directly to the plant (leaves). Of course, in the early years of conversion, some foliar applications may be required while soil imbalance is corrected. The grower needs to demonstrate that measures are being taken to correct the soil. Care must be taken to use materials that are beneficial to soil biological processes and comply with certification standards.

Compost can be a valuable input to be used in conjunction with an integrated soil fertility management program. However, availability, quality, purpose and cost of compost are important considerations, depending on location. Careful consideration must be given to the timing of organic matter decomposition and nitrogen release to ensure this matches the appropriate stage in the trees’ growth cycle.

Some acceptable organic input nutrients may cost more than conventional products. However, the nutrient quantities applied may be less making the costs similar. The table below lists sources of key nutrients.

Plant availability of a number of the nutrient sources listed above can differ from highly soluble conventional products. The lead time required from first applying the input until useful quantities are plant–available must be carefully considered – especially in the first few transitional years. Over time residual pools of nutrients held in soil biomass can compensate for this time lag.

The impact of growing orchard floor cover and producing mulch must also be considered in calculating a nutrient management program.

In some instances too much clover and legume growth can lead to excessive nitrogen levels in soil and have a detrimental effect on fruit quality and storage.

Orchard floor management

The basis of organic orchard floor management is to grow grass to build mulch. Typically a range of preferred species are established that contribute various system functions including:

Generate biomass/organic matter (roots and tops) that feeds soil biological activity as the foundation for sustaining soil conditions, nutrient availability and organic matter cycling:

• build soil structure and improve resilience to soil compaction and erosion
• protect the soil from extremes of water stress, heat and cold
• attract and harbour beneficial predators and biodiversity to minimise pest pressure
• provide competition to suppress problem weeds
• facilitate rapid decomposition of diseased tissue
• improve trafficability
• attract bees and other pollinators.

Establishing floor cover species may include a mix of grass and legume pasture species. Other cover crops may also offer functional benefit or be more suited to local conditions. Careful management to ensure good establishment and persistence of sown cover plants is important, especially the legume component. However, excessive legume dominance can lead to an excess of nitrogen which can affect fruit quality and lead to storage problems.

The aim of building mulch can be achieved by simply bringing in straw. However, experienced growers caution that straw has often been responsible for bringing in too many problems – especially weed problems. An additional issue for mango production relates to avoiding excessive nitrogen release (resulting from decomposition of the organic material) especially during the fruit ripening period.

Costs associated with orchard floor cover management can relate to equipment and labour time for mowing, and additional irrigation costs to grow cover plants over more of the orchard floor.

Irrigation layout - micro-sprinklers

With the aim of growing grass to produce mulch, a number of growers use micro-sprinklers or fan jet sprinklers in place of drippers. This allows a greater area to be irrigated, so the benefits of the cover plants extend over a larger proportion of the orchard floor.

Weed management without herbicides

Attempting organic conversion on a site with serious weed problems will be difficult and expensive. Pre-treatment weed control is considered essential for problem weeds.

Starting with a site that is relatively free from serious problem weeds is an important prerequisite before committing to an organic production system. Vigilant monitoring and timely control of problem weed outbreaks will be important to ensure serious infestations do not get established.

Mowing and mulching

A well established plant cover of preferred species over the orchard floor provides the basis for out-competing and controlling weeds. Managing the orchard floor cover requires periodic mowing and mulching, and these events can be designed and timed to optimise impact on target weeds.

A tractor-mounted mower with spring-loaded retractable outrigger that moves around tree trunks is commonly used. The height and timing of cutting can influence the growth and flowering of different orchard floor species.

For new plantings, heavy straw mulch down rows during the first few establishment years may be useful. The use of barley as an initial cover crop followed by sowing selected orchard floor species can give a solid cover that allows mowing and mulching down the young tree lines. A brush cutter can also used around young trees and other areas where necessary.

In older mango orchards, weed management under stress is usually less problematic due to shading and leaf litter. Seasonal hand weeding of creepers that climb up the tree truck may be required in tropical regions.

Flowering without chemical induction

Mango flowers form from terminal buds of the most recent mature shoots. Most varieties flower once a year during winter or spring following a dormant period. Flower initiation is usually triggered by cool nights and dry conditions.

The most commonly grown mango variety in WA, Kensington Pride, is known to suffer from inconsistent flowering and irregular bearing, especially in climates with a short dormant period. The growth regulating chemical paclobutrazol used by conventional growers to promote flowering is not permitted under organic systems.

The following issues relate to flowering and irregular bearing and should be considered in organic production to minimise costs of these problems:

• Older trees tend to suffer less from irregular bearing than younger trees.
• Flowering can be reduced when tree carbohydrate reserves are diminished as a result of a heavy crop the previous year.
• Early pruning after harvest can improve uniformity of shoot growth and subsequent uniformity of flowering, especially after a heavy crop.
• Mangoes flower from the tips of branches. Pruning to give more terminal branches can lead to more flowers.
• Heavy pruning to reduce tree size can be detrimental to yield for several year.
• Adequate nutrition is important after harvest to ensure good growth and carbohydrate accumulation prior to flowering.
• Too much nitrogen can lead to excessive vegetative growth, often at the expense of flowering.
• Trees need a growth check or dormant period in winter to initiate flowering. Cooler weather and low soil moisture encourage dormancy.
• Withholding water from the tree (after the postharvest flush) for two to three months can help ensure trees enter a dormant phase and improve floral induction. Research in the dry tropics of Queensland showed water stress applied to trees, immediately following maturation of the first summer shoot flush, increased the percentage of terminals flowering (88% vs. 56%) and significantly increased fruit yield (235kg/tree vs. 195kg/tree).
• Late pruning can reduce flowering.
• Tip pruning prior to flowering has been shown to improve flowering in tropical areas. This technique involves lightly pruning trees back to mature wood just prior to flowering.
• Temperatures below 15ºC affect pollen viability. Later flowering in cooler climates can be manipulated by removing early flowers.
• Water stress during flowering can upset flower development and reduce fruit set.
• Wind and insects pollinate mangoes. Wasps, bees and large flies are the most efficient pollinators.
• Boron is important for pollination and fruit development and must be readily available from the soil or applied as a foliar spray prior to bud break.
• Any stress after flowering can increase the number of fruit dropped.

Other approaches to promote flowering and fruit production have been reported. CSIRO has demonstrated that flowering and fruit production of mangoes can be considerably enhanced by cutting a cincture around the tree trunk to induce stress by disrupting sap flow.

Pest and disease management

Mango production in WA has the enviable position of relatively few pests and diseases, and freedom from several serious pests that affect other growing regions. However, for many conventional growers the first question often asked when considering organic production is how do you manage pests and diseases?

Successful organic production requires an integrated approach to managing pests and diseases. An important part involves  underlying preventative strategies that can contribute to minimising the likelihood and severity of problems.

Conventional growers who have adopted integrated pest management (IPM) techniques into their orchard management practices find the transition to an organic system less dramatic than those without IPM knowledge and experience.

All of the principles of IPM can be applied to an organic system with the main variation being that some substances used for specific pest or disease control may need to be changed. Building biodiversity into an organic system by way of establishing and managing the orchard floor to attract and harbour beneficial predators can increase the effectiveness of IPM techniques.

A range of preventative measures is important to minimise susceptibility to pest and disease pressures. Some key preventative measures are:

• Location and regional occurrence – understanding the prevalence, timing and severity of specific pests or diseases for a given location is very important and can have a significant impact on production costs and reliability of production. An organic management plan can be developed to minimise identified risks. For example, southern growing regions need to consider orchard layout, varieties, planting density, tree structure and pruning to avoid conditions that favour fungal attack. Organic mango production in areas prone to wet weather during fruiting is likely to be difficult.
• Surrounding land use – neglected orchards or poorly managed surrounding properties can be a constant source for new outbreaks pest or disease (or weeds). Sometimes unhelpful neighbours can make these sources of pests or diseases a major problem.
• Co-operation with conventional growers is very useful. A local monitoring group for weather and other risk factors can mean less unnecessary sprays. This is important to reduce resistance issues.
• Rootstock and varieties – selection of plant material with resistance characteristics should be used wherever possible. Selecting varieties that are well suited to the local growing conditions will ensure healthy growth and resilience to problems.
• Tree condition and age - successful conversion to organic management can be difficult to achieve with existing tress that are unhealthy and diseased. Older trees may be more easily converted to an organic system than young trees as they may cope better with minor pest and disease pressure. Growth and recovery can also be superior due to less weed pressure and a larger root system to exploit soil reserves of water and nutrients.
• Healthy trees – emphasis on maintaining healthy trees that are naturally able to cope with minor pest of disease problems. The foundation for healthy trees stems from healthy soil. This is achieved via biologically active soil with adequate organic matter and nutrient cycling to balance the chemical, biological and physical condition of the soil. A wide (and increasing) range of inputs is permitted, making it possible to correct any soil imbalance and provide specific supplements as required.
• Canopy management - pruning to an open structure that allows good airflow and adequate internal light without burning fruit can be important to minimise disease risk and assist good fruit colouration.
• Biodiversity – orchard floor management that involves a mix of plant species and timely mowing to encourage and maintain beneficial predators. Windbreaks and shelterbelts can also be designed to encourage biodiversity.
• Hygiene – vigilant and thorough orchard hygiene is very important. Removal of infected wood, fruit and other plant tissue can reduce the severity of subsequent problems.
• Rapid decomposition – infected plant material as a source of future inoculum can be reduced by rapid decomposition assisted by mulch from the orchard floor.
• Proper identification, regular monitoring and timely intervention are essential for successful pest and disease management.

In the event of an outbreak that requires attention, an increasing range of substances is permitted for controlling pests and diseases in organic production.

Some require close attention to timing and frequency of application in order to optimise effectiveness. Target-specific substances should be used in preference to broad spectrum substances, and special attention must be given to any potential impact on beneficial predators. The tables below summarise likely pests and disease issues and their control.

Pest management options

Disease management options

Postharvest treatments

All postharvest operations must comply with organic standards. The primary objective is to avoid contamination with prohibited chemicals and to ensure separation of organic product from any conventional product.

Producers who convert only a portion of their orchard to organic (known as “parallel production”) are likely to have both conventional and organic product moving through the same pack-house. The postharvest procedure normally adopted is to run organic fruit first after the equipment has had a clean-down. This allows the organic product to be dealt with and packed in a separate area prior to commencing the conventional fruit and so avoids the risk of contamination from conventional fruit and related treatments.

HACCP (Hazard Analysis Critical Control Points) based quality assurance systems are ideal for establishing protocols and audit systems that meet organic requirements. Operations with existing HACCP-based QA systems typically find that only minor changes are required to comply with organic standards.

For postharvest disease control the best approach involves ensuring good pre-harvest (in-field) disease management and orchard hygiene together with good postharvest temperature management.

Packing shed hygiene that involves regular equipment cleaning and removal of reject fruit can reduce the transfer of fungal spores onto new fruit. Fruit destined for domestic markets where storage times are short may not require any post harvest treatments for fungal control. Longer term storage and fruit for export are likely to require some form of treatment to reduce fruit breakdown from the diseases anthracnose or stem-end rot.