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
| Pest | Organic management options |
|---|---|
| Scale insects (pink wax scale, mango scale) | Feed on plant sap from stems or fruit. Prefer shadiest parts of the canopy. Can cause sooty mould. Best to treat young (crawler) stage.
|
| Red shouldered leaf beetle | Can build up very rapidly. Causes defoliation and flower death. Not really an issue in Kununurra since the demise of the sugarcane industry, which was the major source of the pest.
|
| Fruit spotting bug | Can build up numbers very rapidly. Control as above. |
| Thrips (flower thrips, red banded thrips) | Causes fruit drop and fruit scaring
|
| Green ants | Efficient predators of a wide range of insect pests and reported (Northern Territory University) to control some of the main pests of mangoes. Cause discomfort for pickers.
|
| Giant termites | Can cause tree death
|
| Fruit fly | Can be a serious problem if not controlled.
|
Disease management options
| Disease | Organic management options |
|---|---|
| Anthracnose | Potential to be greater problem in regions with wet cold winters and wet periods during fruiting. Pre and post harvest control measures may be required.
|
| Stem-end rot | Tends to show as postharvest disease, but infection levels are related to spore loads present in the orchard. Remove dead wood. Spores reside in dead wood, twigs and bark |
| Bacterial spot | More significant problem in southern regions.
|
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.