Introduction to the Problem

Anthracnose is one of the most damaging diseases of olive fruit, caused by several Colletotrichum fungi. In Australia and worldwide, this disease leads to fruit rot, premature fruit drop, and a severe decline in yield and olive oil quality. It tends to strike as olives ripen, posing a serious threat to production - infected olives often fall before harvest and yield only turbid, highly acidic oil of poor quality. Anthracnose is especially problematic in humid olive-growing regions; in Australian groves of susceptible cultivars like Barnea, Manzanillo, or Kalamata, up to 80% of the fruit can be affected in a bad season. The fungus can persist from season to season on plant material, so without proactive management, the disease pressure builds over time. Urgent pre-harvest action is critical, as waiting until symptoms explode at harvest is often too late to save the crop.

Symptoms and Disease Progression 

Olive fruit with anthracnose showing a soft, circular shoulder lesion oozing orange-pink spore masses. As olives approach maturity, anthracnose infection becomes visible as soft, sunken brown rot spots on the fruit (often near the shoulder). Under high humidity, these fruit lesions exude telltale gelatinous, orange or salmon-pink masses of spores on the surface. Affected olives start to look water-soaked or greasy – a symptom sometimes called “soapy olive” due to the slimy appearance. In the early stages, the rot may be localised, but it rapidly expands, causing the olive to collapse into a soft mush. Infections can develop and produce new spore masses very quickly (within about 4 days on a ripe fruit in moist conditions), meaning a small outbreak can turn into a major fruit rot epidemic in under a week if the weather is conducive.

Advanced anthracnose on olives – the fruit has shrivelled, browned, and begun to mummify on the tree. As the disease progresses, many infected olives shrivel, turn brown or black, and dry up. These mummified fruit often remain clinging to twigs or fall to the ground. Clusters of olives on a branch may all become infected, creating a concentration of spore-producing mummies (as shown in the image). Such dried, mummified fruit is a hallmark of late-stage anthracnose and serves as a reservoir of the fungus. In severe cases, you may find twig dieback associated with heavy fruit infection – the fungus can invade pedicels and stems, causing leaves on that shoot to wilt and die. Anthracnose can also occasionally infect flowers in spring (blossom blight), causing brown, withered blooms that drop off, though early symptoms often go unnoticed. Generally, olives show no external sign of infection until they begin to ripen, at which point lesions erupt and spore masses spread to neighbouring fruit in the canopy. 

Olive branch with multiple anthracnose-infected fruit. Many olives exhibit dark, sunken lesions and fungal spore masses, and some have dried into mummies. Without intervention, an anthracnose outbreak can escalate rapidly as harvest time nears. Infected olives may drop to the ground in large numbers, resulting in direct yield loss. Those that remain on the tree are often unusable – when pressed, they yield oil with elevated free fatty acids and unpleasant flavours, unsuitable for extra virgin grade. The disease cycle can carry over into the next season via the persistent mummified fruit and any infected twigs left on the tree, so the severity may increase each year if not managed. Thus, recognising anthracnose symptoms early (and implementing controls) is vital to preventing extensive crop and quality losses. 

Biology and Infection Cycle of Colletotrichum in Australia 

Anthracnose in olives is caused by a complex of fungi in the genus Colletotrichum. Traditionally, C. acutatum and C. gloeosporioides were identified as the culprits, but taxonomists have since split these groups into multiple species. In Australia, at least three Colletotrichum species are known to cause olive anthracnose (C. acutatum, C. gloeosporioides, and C. simmondsii), with additional species reported overseas. All produce a similar syndrome on olives. The pathogen’s life cycle allows it to survive between seasons and infect the host at multiple points: - Overwintering: The fungus persists on infected plant debris, especially mummified olives that remain on the tree or ground, and can also survive in infected twigs or leaves. These serve as the primary inoculum sources in the new season. The fungi form masses of conidia (spores) on these residues, which are spread by winter and spring rains. (Insects and birds can also passively transfer some spores on their bodies, though rain-splash is the main dispersal mechanism.)

• Primary infection in Spring: During spring, when olive trees flower and set fruit, the anthracnose spores germinate and infect flowers, young fruit, and sometimes leaves. Prolonged wetness is required – at least 24–48 hours of moisture on the tissues – and moderate warmth (10–25 °C, with an optimum around 17–20 °C) for infections to occur. If wet, humid weather coincides with bloom or fruit set, the fungus can invade these tissues. Notably, infections at this early stage remain latent: the fungus may colonise the surface or tissue of the olive without immediate symptoms. The young fruit typically continues to develop normally over summer, harbouring quiescent infections. (Latent infection is why anthracnose is considered a “stealth” or latent disease – the damage often isn’t apparent until much later .) Leaves or shoots that become infected in spring may show some lesions or dieback, which can further harbour the pathogen. 
• Secondary infection cycles: As autumn arrives and fruits begin to ripen, the latent infections activate. If rain or heavy dew events occur in the ripening period, those initially infected olives swiftly develop the characteristic rot and spore masses. The now-symptomatic fruit becomes a new spore source, releasing millions of conidia that rain-splash onto other olives, causing secondary infections on any remaining healthy fruit. Warm, wet weather during the harvest period greatly accelerates this cycle – new infections can produce a new generation of spores in just a few days under ideal conditions. This can lead to an exponential spread in the canopy just when the fruit is nearing maturity.
• Cycle continuation: After harvest, any infected fruit left behind will mummify and retain the fungus. These mummies (along with infected twigs or leaves) carry the pathogen through winter. The following spring, they kickstart the cycle again by releasing spores with the rains. The disease may thus build up each year if infected material isn’t removed, especially in climates where frequent spring/ autumn rains provide regular infection opportunities. 
  

Impacts on Oil Quality and Yield

Anthracnose directly reduces olive yields and can essentially ruin the crop’s marketable value. Infected flowers may lead to blossom drop or poor fruit set, and later infection causes fruit rot and drop before harvest. It’s not uncommon for heavily infected trees to lose a large portion of their olives to the ground before picking. Those fruits that remain on the tree are often badly rotted or desiccated and contribute little to the yield. Australian growers have reported crop losses ranging from 10–50% in moderate outbreaks to nearly total loss in extreme cases on very susceptible cultivars.

Quality degradation is a major concern even for the portion of the crop that can be harvested. Oil produced from anthracnose-infected olives is of much lower quality than oil from healthy fruit. The rotting process raises the free fatty acid levels and peroxides in the fruit, resulting in rancid or “fusty” off-flavours and high acidity in the oil. Even a relatively small percentage of diseased olives in a press batch can downgrade the entire lot of oil. For example, field observations suggest that if around 15–20% of the olives going into the mill are anthracnose-infected, the oil will likely fail to meet Extra Virgin standards. In practice, oils from anthracnose-affected fruit are often only suitable for lampante (non-food) oil due to excess acidity and defects. Aside from acidity and flavour issues, the pigments from the fungal decay can give the oil an abnormal dark, cloudy appearance (sometimes described as a reddish or brownish turbid oil). This makes anthracnose not only a yield robber but also a threat to achieving quality premiums — growers may end up with substantially reduced income even from the portion of the crop that is salvaged.

Additionally, severe anthracnose can cause longer-term impacts on the olive trees themselves. Heavy defoliation or twig dieback from infection can weaken trees and reduce the following year’s flowering wood. Repeated epidemics in successive years, therefore, can have a cumulative debilitating effect on orchard productivity. For all these reasons, anthracnose is considered a critical disease to manage for both yield and quality – preventing the disease is far more effective than trying to salvage a heavily infected crop at the last minute.

Conditions that Favour Disease Spread 

Anthracnose thrives under specific environmental conditions that are unfortunately common in parts of Australia. The fungus requires moisture and warmth to infect and spread. Extended periods of leaf wetness (from rain, heavy fog/mist, or even over-irrigation) are the single biggest factor driving outbreaks. Spores germinate and penetrate olive tissues only when free water is present for many hours. Thus, a prolonged autumn rain or back-to-back days of drizzle and dew can trigger a wave of new infections just as fruit is ripening. The disease is favoured by high humidity and rainy weather at temperatures around 10–25 °C. The optimal temperature for anthracnose development is about ~18 °C (typical of mild humid spring or autumn days), but infection can occur over a broad cool–warm range as long as moisture is available. Hot, dry conditions, on the other hand, tend to suppress the disease, which is why anthracnose is seldom a problem in arid inland groves or during drought years.

Climatically, anthracnose is most severe in regions with summer or early autumn rainfall patterns. In Australia, groves in parts of Queensland and New South Wales (where warm-season rains and humid late summers are common) experience much higher anthracnose pressure than those in Mediterranean-type climates (e.g. South Australia or Western Australia’s olive regions with dry summers). A sudden unseasonal rain spell before harvest in an otherwise dry area, however, can still cause localised outbreaks, so no region is completely immune if the weather turns wet at the wrong time. 

Within the grove, microclimate and cultural conditions also influence disease spread: - Canopy Density and Airflow: Trees that are densely foliated or closely planted retain more moisture in the canopy after rain. Poor air circulation means fruit and leaves stay wet longer, greatly increasing infection risk. It’s been observed that high-density and super-high-density plantings can see faster anthracnose development compared to widely spaced trees. Similarly, unpruned trees with dense interiors create a humid microclimate ideal for the fungus.

• Overhead Irrigation and Drainage: Overhead sprinkler irrigation or lack of drainage can simulate the prolonged wetness that anthracnose loves. Continual wetting of foliage/fruit (or waterlogging, which increases humidity) will favour the disease. Growers in anthracnose-prone areas should avoid excessive overhead watering, especially as fruit nears maturity. 
•  Inoculum Levels: If the grove had a history of anthracnose and many mummified fruits remain, even a short wet period can lead to a quick flare-up because there are abundant spores ready to go. Conversely, a grove that’s never had anthracnose might withstand a brief rain with minimal infection (due to lack of spores present). Unfortunately, once anthracnose establishes, spore inoculum tends to accumulate year over year if not aggressively managed. This is why the disease can seem minor initially, then “explode” after a couple of conducive seasons.
  
• Cultivar Susceptibility: As noted, certain olive varieties are more prone to infection. Having a block of a very susceptible cultivar increases the likelihood of disease spread (and even nearby less-susceptible trees can receive a high spore load from those infection centres). For instance, if Barnea trees (highly susceptible) are mixed in an orchard, they can act as a nucleus for anthracnose in a wet year, spreading spores to neighbouring rows. 

Integrated Management Strategies 

Managing olive anthracnose in Australia requires an integrated approach, combining cultural practices, careful monitoring, and strategic use of fungicides. The goal is to prevent or greatly reduce infections before they take hold, because once the fruit is rotting, options are limited. Below are key strategies: 

Cultural Controls (Orchard Hygiene & Canopy Management): 

The foundation of anthracnose management is reducing the sources of the fungus and making the canopy less hospitable to it. A top priority is orchard sanitation: - Remove and destroy mummified fruit – After harvest (and even during the season), growers should remove any dried, blackened “mummy” olives that remain on the trees. These mummies are loaded with spores and will rain down infection in the next wet spell. Table olive growers often hand-pick remaining fruit; oil olive growers may need to strip or knock off leftover fruit and rake up fallen ones. Completely removing them from the grove or deep-burying them helps break the cycle. It’s laborious, but it can significantly cut back spring spore inoculum. 

• Prune for an open canopy – Regular pruning to increase air flow and sunlight penetration into trees is critical. An open canopy dries faster after rain, reducing the wetness duration that the fungus needs. Pruning also lets fungicide sprays penetrate more effectively. Remove dense interior shoots and any dead or diseased twigs (those with dieback or remaining fruit stems from infected olives) and destroy that pruned material off-site. Pruning is best done during the dry season or winter dormancy; avoid pruning in wet conditions to prevent spreading spores on tools (disinfect pruning equipment if anthracnose is present). Proper canopy management not only helps with anthracnose but also improves overall tree health and productivity.
  
• Avoid highly susceptible cultivars in high-risk areas – Where possible, choose olive varieties that are less prone to anthracnose if you are planting in a humid or summer-wet region. For example, Barnea has shown extreme susceptibility in Australia, so it may be wise to avoid planting Barnea in anthracnose-prone climates. If you already have susceptible varieties, be extra vigilant with those blocks – they might need more intensive monitoring and fungicide protection. In contrast, more tolerant varieties (like Picual or Frantoio) can be planted in higher-pressure areas with a lower risk of severe loss (though not zero). 
  
• General grove hygiene – Clean up leaf litter and dead wood, as these can harbour other pathogens that might complicate disease management. While Colletotrichum primarily overwinters in fruit mummies, a healthy, well-maintained grove will better resist all diseases. Also, sanitise picking bins and equipment that might carry spore-laden pulp or debris from an infected grove to a clean one. It’s rare but possible to transfer anthracnose via contaminated equipment or clothing, especially when handling squashed infected fruit, so if moving between groves, basic sanitation can’t hurt. 
  

• Regular monitoring is vital to time interventions and assess effectiveness: - Inspect trees at key times – From spring through harvest, growers should routinely scout the orchard. In spring, check for any blossom blight or early fruitlet rot (though uncommon, flag it if seen). More critically, as fruit begins to ripen (colour change), inspect a sample of olives closely each week for any tiny brown sunken spots or signs of orange spore ooze. Early detection of a few infected fruit can warn you that anthracnose is active, giving a chance to act (for instance, applying a fungicide before it explodes). Look especially in the denser parts of trees and lower branches, where humidity is higher.
• Weather monitoring – Pay close attention to weather forecasts, especially in the lead-up to harvest. If a significant rainfall event or period of high humidity is predicted when olives are near ripe, consider protective measures (like a preventative spray) ahead of that weather. Some growers use disease forecasting models based on temperature and leaf wetness duration – while formal models for olive anthracnose are still under development, a practical approach is to note when conditions (e.g. two days of rain with mild temperatures) could trigger infections and treat proactively. 
  
• Spore trapping or lab testing – In research settings, spore traps or monitoring kits can detect Colletotrichum spores in the orchard air. While not commonly used by growers, knowing spore presence could theoretically guide sprays. More pragmatically, growers can send suspicious fruit samples to a lab (or DPI pathologist) for confirmation if unsure whether a fruit rot is anthracnose or something else. But typically, the field signs (orange-pink spore masses on rotting fruit) are distinctive enough for on-site diagnosis.
  
• Record and learn – Document which blocks or varieties get anthracnose and under what conditions. Often, the disease will start in one part of a grove (for example, a low-lying section that stays damp or a block of a vulnerable cultivar). Identifying these hotspots allows targeted management – you might spray those sections first or more frequently, or harvest those blocks early to minimise exposure.
  

Chemical intervention is an important tool, used in conjunction with the above cultural practices and guided by monitoring. Fungicides are most effective when applied preventatively or at the very earliest stage of infection, rather than trying to “cure” heavily diseased fruit. In Australia, there are a few fungicide options available (see next section for specific products). Spray timing and coverage are critical: - Protective sprays around flowering and fruit set: Research and expert recommendations indicate that the pre-flowering through early fruit set period is a critical infection window for anthracnose. Even though symptoms won’t show until much later, applying fungicides during this period can greatly reduce the number of latent infections that establish. For example, a common strategy is two sprays – one at early bloom (white bud) and another at the small fruit stage – in spring if conditions are wet. This can protect flowers and young olives from that primary infection wave. Copper-based fungicides are often used here (they help against other diseases like peacock spot too), or other permitted fungicides can be applied according to label/permit.

• Cover sprays before autumn rains: If significant rain is forecast during the ripening period, a preharvest protective spray is highly advisable on susceptible blocks. A fungicide application in late summer or early autumn, timed just before a rain front, can protect the fruit from new infection and possibly slow any existing infections from sporulating. This is essentially an “insurance” spray to prevent an epidemic as you approach harvest. Copper fungicides or a systemic like azoxystrobin (under permit) are options here, keeping in mind any withholding periods before harvest.
• Continue if conditions persist: In a very wet season, multiple sprays may be needed. Fungicides generally provide a protective window of around 2–3 weeks, but heavy rain can wash residues off. Growers in high-pressure, wet conditions often follow a schedule of sprays at 3–4 week intervals from spring through harvest, focusing on times when rain is likely. For instance, in parts of Queensland, some growers spray copper every 4 weeks from flowering until picking as a preventative measure. The cost of multiple sprays has to be weighed against the potential crop loss (in severe anthracnose areas like parts of Spain, routine fungicide programs costing hundreds of dollars per hectare are standard ). Each grower should tailor the spray frequency to the orchard’s disease history and climatic risk. 
  
• Fungicide selection and rotation: Use fungicides that are effective against anthracnose and rotate chemical groups to avoid resistance. Copper formulations provide broad-spectrum protection, and the fungus has virtually no resistance to copper (since it’s a multi-site contact fungicide). Strobilurin fungicides (Group 11, e.g. azoxystrobin or pyraclostrobin) are highly effective systemics against anthracnose, but they should be rotated or mixed with other fungicides because fungi can develop resistance to single-site modes of action. In some crops, Colletotrichum resistance to strobilurins has been reported, so we use them judiciously. A typical rotation might be copper, then a strobilurin, then copper again, etc., if multiple sprays are needed. Also note that azoxystrobin (Amistar®) can be phytotoxic to some apple varieties, so avoid drift if you have apple orchards nearby.
  
•  Application techniques: Ensure thorough coverage of the trees when spraying. Anthracnose often starts high in the tree or in thick canopies, so complete coverage (including the tops of tall trees) is important. Use sufficient water volume and consider spray additives/spreaders to help cover fruit surfaces. Poor coverage leads to gaps in protection, which the fungus can exploit. If your trees are very large and hard to spray, aggressive pruning (to reduce tree size) might be needed as part of the integrated approach, since incomplete spray coverage on large trees is a known issue with anthracnose control. 
  

Fungicide Options – Registered and Permitted Chemicals 

Several chemical controls are available (either fully registered or via permit) for anthracnose in olives. Always check current APVMA registrations and permits for up-to-date usage instructions, rates, and withholding periods, as these can change. As of the mid-2020s, the key fungicide options include:

• Copper-Based Fungicides (Group M1) – Copper hydroxide, copper oxychloride, and tribasic copper sulphate formulations are widely used as protectant fungicides against anthracnose and other olive diseases. Copper is registered for olives in Australia (e.g. some copper products have a 1-day WHP on olives). Copper is applied preventatively; for example, copper hydroxide sprays from flowering through fruit development (repeated every few weeks in wet weather) can significantly suppress anthracnose. Copper fungicides are also organically acceptable in olive production. They work by creating a protective film that kills spores on contact. Note that copper is best used before infection – it has limited curative action once the fungus is inside the fruit. Good coverage is essential, and excessive use can cause leaf spotting or build-up in soils, so follow label rates.  
• Azoxystrobin (e.g. Amistar® – Group 11) – A systemic strobilurin fungicide that is highly effective against anthracnose. In olives, azoxystrobin use has been under a minor-use permit (e.g. Permit PER14580) for anthracnose control. It can protect developing fruit and also has some curative activity (it inhibits fungal growth within tissues). Typically, a maximum of two applications per season is allowed, with a 3-week re-treatment interval and a pre-harvest withholding period (21 days under past permits). Azoxystrobin should be rotated with non-Group 11 fungicides to manage resistance. It’s a good option to apply just before a high-risk weather period, as it can move into plant tissue and provide protection for a couple of weeks. Growers should ensure any permit conditions (such as not spraying near sensitive crops like apples, as mentioned earlier) are followed. 
  
• Pyraclostrobin + Metiram (Aero® – Groups 11 + M3) – This is a pre-mix of a strobilurin (pyraclostrobin) with a contact protectant (metiram). It has been used under permit in olives (Permit PER14908) for anthracnose. The combination of a systemic and a multi-site fungicide offers protective and some curative action. Like azoxystrobin, only two sprays per season were permitted, with similar timing restrictions. If available, this product can be effective, but note metiram (like mancozeb) has a 21-day WHP, and the product should not be used too close to harvest. As with any strobilurin-containing product, avoid back-to-back Aero sprays – rotate with copper or other chemistry. 
  
• Mancozeb (Group M3) – A broad-spectrum protectant fungicide (multi-site mode of action) that has been used under permit for olive anthracnose in the past. Mancozeb acts similarly to metiram (both are EBDC fungicides), providing a protective barrier on fruit. It was typically allowed as a few applications up to mid-season (older permits had it not too close to harvest). Mancozeb can help as part of a rotation (it’s a different mode of action from copper and strobilurins), though by itself it’s less commonly used than copper for olives. Growers should check the current permit status for mancozeb on olives, as regulations may have changed since the previous permits (which expired in 2018 ).  
  
• Other fungicides – Research is ongoing into other fungicides for anthracnose. In some countries, fungicides like tebuconazole (a DMI/triazole) or fludioxonil have been tested on olives. However, in Australia, these are not currently registered or widely permitted for olives. Always refer to the latest Australian Olive industry guidelines or APVMA resources for new permits. Also, always adhere to label or permit conditions (rate, timing, PPE, etc.) for any chemical use.
  

Recommendations for Preventive Action and Good Hygiene

To wrap up, here is a summary checklist of preventative measures and hygiene practices for managing olive anthracnose. Adopting these practices before the disease gets out of hand will pay off at harvest:

• Remove all old fruit (“mummies”) from trees and ground during and after harvest. Dispose of them far from the grove (burn, bury, or trash) to eliminate overwintering inoculum. This is one of the most effective ways to reduce disease carryover. 
• Prune and destroy diseased twigs/branches during the dormant season. Cut out shoots showing dieback or withered fruit stems, as they may harbour the fungus. Also, prune generally for an open, airy canopy – sunlight and airflow will suppress fungal growth and dry out moisture faster.
• Optimise irrigation and drainage. Avoid overhead irrigation, or if used, water in the early morning so foliage dries quickly. Do not over-water; excessive humidity and wet feet encourage anthracnose. Ensure good drainage to prevent standing water or overly humid microclimates in the grove. 
• Plant resistant or less-susceptible cultivars in high-risk climates. For new groves in humid/ rainy areas, consider varieties like Arbequina or Picual. If susceptible varieties (e.g. Barnea, Manzanillo) are grown, be prepared to manage them intensively or harvest early to escape serious disease. 
• Apply preventive fungicides at critical times. Protect the crop with well-timed sprays (for example, at flowering, fruit set, and pre-harvest if needed) when wet weather is anticipated. Don’t wait for severe symptoms – preventative action is far more effective. Rotate fungicide modes of action and follow label/permit directions. 
• Monitor vigilantly. Scout your grove regularly for early signs of anthracnose, and track weather forecasts. If you catch the first signs of infection or forecasted risk conditions, you can implement controls (spraying, early harvest, etc.) before it’s too late. 
• Maintain overall grove health. Balanced fertilisation and minimising other stresses can help trees resist infections. While anthracnose largely depends on wetness, a robust tree may suffer less damage and recover faster. Conversely, a stressed tree (nutrient deficiencies, other pests) may be more prone to severe outbreaks. 
• Harvest promptly in risky seasons. If your region is entering a wet period and fruit is nearing maturity, consider harvesting olives as early as feasible. Anthracnose damage accelerates the longer the ripe fruit hangs in wet conditions. An early harvest can sometimes dodge the worst of an epidemic (though oil yields might be slightly lower, it’s better than losing the crop entirely). 
• Practice good sanitation between groves. If equipment, bins, or workers move from an infected grove to another grove, clean off any plant debris or fruit residues to avoid transferring spores. It’s a minor concern relative to wind and rain spread, but good biosecurity can help limit new introductions of the pathogen.

By following these preventative and hygiene steps, growers create an environment where the anthracnose fungus struggles to get established. The key is to be proactive – once orange spores are running down your olives, the damage is largely done. Australian industry experts emphasise taking action before harvest time to protect your crop. With vigilance and an integrated strategy, even growers in higher-risk regions can successfully manage anthracnose and deliver healthy olives to the press.

• 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 mould, or anything unusual.

Proactive, weekly management is essential for a successful grove.

If you need further assistance, please contact us.

Occasionally a sap-sucking insect known as Brown or Black Olive Scale will be seen on olive trees. It is rarely a problem if the trees are in good health. We usually only spray our mature trees for scale every two to three years and only then if they need it. However, certain areas of Australia are more prone to the scale.

If your olive tree has black spots on branches or an infestation of black scale, it's crucial to act quickly. Scale on olive trees, including black olive scale, appears as dark bumps that weaken growth. For black scale treatment, use a proven treatment, introduce beneficial insects, and prune for better air circulation. If you're wondering how to get rid of black scale on an olive tree, early detection and prompt action are key to protecting your grove.

About

The adult females are very easy to recognise on the olive tree stems. They are dome shaped, dark brown to black in colour, and about the size of a match head.

The tiny eggs laid under the female, look like piles of very fine sand. Mainly during the summer, these eggs hatch into tiny, six-legged, cream coloured ‘crawlers’. The crawlers move up the stems and usually settle along the veins of young leaves. At this stage they don’t have the impervious shell of the adult and can usually be killed with one or two applications of white oil about two weeks apart. White oil should be used only as directed on the label by the manufacturers (and by your agricultural department) and never during the hot part of the day. It puts an oil film over the young ‘crawler’ and suffocates it. If applied in the hot part of the day it also stops the leaves from breathing properly and can be detrimental to the tree. The White oil application will also tend to rid the tree of ‘sooty mould’ as discussed soon.

If the crawlers are allowed to live, they will moult after about one month and then migrate to the young stems and twigs of the tree. Here they will mature and lay more eggs and their protective brown shells will be impervious to white oil. Squash the scale between your fingers to see if it is alive. If it is alive, then your fingers will be wet from the juices squeezed out. If it is dead then your fingers will be dry and dusty.

Bad infestations of live mature scale may need spraying with an insecticide such as Supracide. (Important: See note regarding “Treatment”) In Greece, Supracide is the main spray used for most olive problems. Once again, check with your local agricultural chemical supplier and the product label, for directions.

Probably the damage done by the scale itself to the tough olive tree is negligible compared with what happens next.

As the scale feeds, the ‘manure’ they excrete is a sweet, sticky, ‘honeydew’. This excreted sticky liquid can finally cover the leaves of the entire tree. A fungus known as sooty mould feeds on this food and multiplies until the entire tree may be covered with the black sooty mould. This is where the real problem lies.

The leaves are coated with the black deposit, so the sun’s light can’t penetrate the leaves properly. Therefore photosynthesis can’t take place efficiently. Therefore, ‘root producing’ food is not manufactured in the leaf. Therefore roots don’t develop properly. Therefore the poor root system can’t collect enough food and water from the soil to send up to produce more leaves, which in turn will produce more root. Once the vicious cycle begins, a stunted and unhealthy tree with poor crops is the result.

To make the problem worse, sweet ‘honeydew’ on the leaves also attracts large numbers of ants. It appears that as the ants constantly move over the scale, they frighten away the small wasp parasites which in normal cases would keep the scale under control.

Black Olive Scale Gallery

The good news is that healthy olive trees don’t get the scale, sooty mould, and ant infestation to any great extent. More good news is that heavily infested trees are easily fixed.

Normally, one thorough spraying of the entire tree and soil below with a systemic insecticide will be adequate. Nevertheless, to be sure, a second spray about two weeks later may be worthwhile.

Now, if there is no more live scale, there is no more eating, therefore no more ‘honeydew’ excreta, therefore no more sooty mould and ants. Over a period of time the dead sooty mould deposit will peel off the leaves from exposure to the rain, wind and sun. The green leaf surface will be exposed and growth will continue as normal. Treat the tree to an occasional feeding of Seagold fertilizer/mulch and foliar application and some water and watch its health come back.

Admiral Advance by Sumitomo for control of Black Olive Scale
** DELIVERY INCLUDED in Australia
EAdmiral
$315.00(ex tax)

Pybo - Natural Pyrethrum Contact Insecticide 24 hour withholding period!
Solvent-free botanical insecticide for fast-acting, broad-spectrum pest control.
EP0
$246.90(ex tax)

Pyganic Insecticide - Organic Pest Control
Certified Organic Botanical Crop Protection
EA.PyGa
$149.25(ex tax)

Seaweed Extract Composted Seaweed Fertiliser - SEAGOLD
100% natural powdered seaweed extract
EA09
$75.00(ex tax)

Sumi-Alpha Flex 20L
Dual-use insecticide for controlling insects and mites
EA.ALPHA
$480.00(ex tax)

VOLPI POWERCUT Cordless Electric Secateurs
Delivery will be calculated separately
CA.ELECTRO.VOLPI.POWERCUT
More Info

Scientific Name:  Saissetia oleae

DESCRIPTION OF THE PEST

Black scale adult females are about 0.20 inch (about the size of a match head) in diameter. They are dark brown or black with a prominent H-shaped ridge on the back. Young scales are yellow to orange crawlers and are found on leaves and twigs of the tree. Often, a hand lens is needed to detect the crawlers. Black scale usually has one generation per year in interior valley olive growing districts. In cooler, coastal regions multiple generations occur. Black scale prefers dense unpruned portions of trees. Open, airy trees rarely support populations of black scale.

DAMAGE

Young black scale excretes a sticky, shiny honeydew on leaves of infested trees. At first, affected trees and leaves glisten and then become sooty and black in appearance as sooty mould fungus grows on the honeydew. Infestations reduce vigour and productivity of the tree. Continued feeding causes defoliation that reduces the bloom in the following year. Olive pickers are reluctant to pick olive fruits covered with honeydew and sooty mould.

CULTURAL CONTROL

Pruning to provide open, airy trees discourages black scale infestation and is preferred to chemical treatment.

BIOLOGICAL CONTROL

A number of parasites attack the black scale, the most common are Metaphycus helvolus, Metaphycus bartletti, and Scutellista cyanea. These parasites, combined with proper pruning, provide sufficient control in northern and coastal orchards. In other regions, biological control is often ineffective because the black scale’s development pattern hampers parasite establishment.

ORGANICALLY ACCEPTABLE METHODS

Cultural and biological control and oil sprays. Organic pyrethrum sprays like Pyganic ( Pybo is no longer organically certified).

WHEN TO TREAT

If infestations are resulting in honeydew, treat the crawlers. In interior valleys, delay treatment until hatching is complete and crawlers have left protection of the old female body. Once crawlers have completely emerged, a treatment can effectively be made in summer, fall or winter provided the scales have not developed into the rubber stage (later second instar, which are dark, mottled grey, and leathery, with a clear H-shaped ridge on the back).

TREATMENT

Due to the chemical nature of the treatments, Please check with your agricultural chemical supplier as to the suitability, application and safety precautions of your chosen scale treatment for olives. Some growers have used Summer or Petroleum Oil and Supracide.  Californian olive growers use Oil Emulsions, Diazinon 50WP, Methidathion and Carbaryl. The use of chemicals reduces the microbial population in your soil and can inhibit the uptake of certain nutrients to your trees.  Harmful residues of chemicals can also build up in your soil structure.

A new product Admiral has become available which acts as an insect growth regulator rather than a kill-on-contact pesticide, it has been quite effective and like any treatment of scale; timing is essential.  Ants can be controlled with an Ant Bait suitable for Horticultural use.  We suggest Distance Plus Ant Bait.

• Admiral Advance
• Pybo
• Pyganic
• Distance Plus Ant
  

References

“Olives – Pest Management Guidelines” (UCPMG Publication 8, 1994). These guidelines cover the major olive problems found in Australia and California and are available for free from their website http://www.ipm.ucdavis.edu/PMG/selectnewpest.olives.html . (The information comes from California so all references to places, seasons, months and treatments are Californian). If you have any questions, please contact The Olive Centre, PH: 07 4696 9845, Email: sales@theolivecentre.com.au

Admiral Advance by Sumitomo for control of Black Olive Scale
** DELIVERY INCLUDED in Australia
EAdmiral
$315.00(ex tax)

Pybo - Natural Pyrethrum Contact Insecticide 24 hour withholding period!
Solvent-free botanical insecticide for fast-acting, broad-spectrum pest control.
EP0
$246.90(ex tax)

Pyganic Insecticide - Organic Pest Control
Certified Organic Botanical Crop Protection
EA.PyGa
$149.25(ex tax)

Seaweed Extract Composted Seaweed Fertiliser - SEAGOLD
100% natural powdered seaweed extract
EA09
$75.00(ex tax)

Sumi-Alpha Flex 20L
Dual-use insecticide for controlling insects and mites
EA.ALPHA
$480.00(ex tax)

VOLPI POWERCUT Cordless Electric Secateurs
Delivery will be calculated separately
CA.ELECTRO.VOLPI.POWERCUT
More Info

This summer cropping season is facing unprecedented challenges in fertiliser supply. Availability of MAP fertiliser (monoammonium phosphate) and DAP fertiliser (diammonium phosphate) is expected to remain extremely limited worldwide, with serious implications for growers planning their nutrient programs.

Why is Fertiliser Supply Tight

China’s Export Restrictions Continue

Since 2021, China has imposed strict quotas and inspection rules on phosphate fertiliser exports to protect domestic prices and safeguard food security. 

The impact has been dramatic:

• March 2025 exports: just 13,000 tonnes, compared with 950,000 tonnes in March 2022.
• Q1 2025 exports: 111,000 tonnes, versus a three-year average of 785,000 tonnes.

Other Suppliers Cannot Fill the Gap

Although Morocco, Russia, the USA, and Saudi Arabia also produce MAP and DAP, they cannot offset the sharp drop in Chinese exports. 

The result is:

• Rising global fertiliser prices
• Longer delivery lead times
• Stricter supplier allocations
• Reduced pricing flexibility across the summer cropping season

What This Means for Growers

For olive growers and other professional producers, the impacts are already being felt:

• Reduced fertiliser availability for summer cropping
• Higher input costs with delivery delays
• Less flexibility in nutrient timing and program planning

Our Recommendations - Secure Your Supply Now

Do not wait for traditional ordering windows. Place orders immediately and consider forward contracting for next season. Securing current pricing now helps protect your operation against higher costs and potential shortages later.

Optimise Your Nutrient Strategy

• Review alternative phosphate fertiliser options
• Adjust application rates where agronomically feasible
• Consider split applications to maximise nutrient efficiency
• Explore precision application technologies to reduce overall fertiliser requirements