RECENT struggles within the farming industry have revived a long-standing conversation about plant diseases and pathologies affecting crops amid record heatwaves and shifting climate patterns. With local growers facing an increase in plant diseases, plant pathologists have become a vital resource within the farming industry. 

From fungal infections in vineyards, to emerging bacterial threats in citrus orchards, the battle against plant pathologies has intensified, and as farmers race to adapt, the Riverland’s struggle underscores a larger truth: modern agriculture’s resilience may depend on how quickly it can respond to these evolving biological threats.

Plant pathology experts warn that traditional methods of disease control might be one of the best solutions to tackle the most common pathologies and diseases. 

Peter Magarey is one of Australia’s lead pathology experts, with more than 45 years of experience in researching plant pathologies, diseases and ground-breaking solutions to minimise their effect on grapes, almonds and citrus plants.  

“Speaking about grapes, the most common diseases found are downy mildew and powdery mildew, having different characteristics and treatments," Mr Magarey said. 

“For almonds, there's a disease called phytophthora, which is a root rot and it is caused by overirrigation and soils remaining wet for too long. That's a major one because it starts to rot the trunks of the tree, and that affects the whole tree.

“Powdery mildew has been around since the very early days of the grapes coming into Australia, and downy mildew didn't start here until 1917. It was a very wet year, which favoured the disease.

“There is a disease called huanglongbing (yellow dragon disease), previously known as citrus greening, which has caused huge devastation in South and North America, but fortunately for the moment, it hasn’t been detected in Australia. That would be a devastating hit to the Australian citrus industry."

Climate variations, soil conditions and irrigation systems can have a shifting impact on the spread of several plant diseases, potentially affecting not only small crops, but also affecting other plant variations that are vital to Australia’s ecosystem.

That valuable information is something Mr Magarey learned while growing up on an orchard in the Adelaide Hills, which gave him the necessary knowledge to understand, at first, how the weather could affect different crops, and their ability to manage it. 

He went on to study Plant Pathology at Adelaide University, and moved to the Riverland in 1976 to pursue a career within the region. Since then, he has become one of Australia’s best plant pathologists, working with private and public agencies towards improving the life expectancy of crops.

“I believe the Lord wanted me to be here, so I have enjoyed it all, especially working with the grape industry, which is to be complimented for their adoptive approach,” Mr Magarey said. 

“The attitudes have changed with new machinery, and they learned about it, they inquired about it, and we've worked together as a team.

“For effectively 30 years, the Riverland has been leading the way in Australian viticulture for disease control measures using systems like GrowCare. 

“The growers' attitudes have changed as they've seen it working, it’s a gradual process, but, they changed, adopted, developed and helped advance the whole system."

Mr Magarey said “the influence of most diseases is controlled by weather conditions, and diseases, like downy mildew, can spread if you have a certain amount of rain, for a certain period of time."  

“The rain spray and moisture will increase the disease's ability to grow, germinate and spread within the soil, creating new spores in other plants," he said.

"For downy mildew, they release a spore called swimming spore, or zoospore.”

“Zoospores need rain splash to move around and stay, in aerosol form, within 10cm-to-20cm above the soil, and when they find a droplet of water, they float around into leaves and other plants. Having the right temperature and moisture conditions, for long enough, definitely helps them to survive.”

Mr Magarey said powdery mildew is less dependent on weather, so it can become a more-common disease, especially in grape vines, but the one that can seriously affect these types of plants is downy mildew. 

“Downy mildew used to be a big issue in grapes when I came to the Riverland in 1976, as it wasn’t very well known,” Mr Magarey said. 

“Even though it was introduced in 1917, the conditions that actually controlled the disease weren’t really known, and during the big droughts and dust storms of the 1940s, the disease got a head start.

“Between the 1950s and 1970s the disease spread across Australia, with weather conditions being favourable, it raised awareness with farmers who asked themselves, what can we do?”

At the time, Mr Magarey started working on the epidemiology of downy mildew, alongside researchers from Europe and the United States, trying to understand how the disease spread according to different weather conditions, and how the Australian environment affected its capability to grow.

“From that research, we developed a wonderful international team that worked on downy mildew, getting to important conclusions about when not to spray for the disease, or when to actually spray for it. We did that by understanding its epidemiology and how it behaved with our changing climate.

“We designed a new revolutionary system for downy mildew control called GrowCare, a computer data-based platform to advise growers when to spray or not, depending on data collected across the regions.

“GrowCare, which we still use today, saved the farming industry a lot of money, especially the grape industry, because it gives farmers real-time data and alerts about certain diseases affecting the region, and advises them about the need of spraying their vineyards.

“With downy mildew on grapes, we knew about the conditions under which it spreads and built a simulator of disease, (GrowCare), where we put in the weather data, process it through the black box, and deliver an outcome in terms of disease risk by virtue of how favourable were the conditions.

“On that outcome, we would know how to spray, or when to spray and when not to.”

When it comes to management and prevention of diseases, experts controlling the microclimate within the crops is of vital importance to maintain healthy vines and almond trees.

“With almonds, controlling soil moisture and time between drying periods, gives growers the capacity to manage their crops in a chemical-free environment,” Mr Magarey said. 

"It’s more a management issue rather than a chemical treatment

“With diseases like downy mildew on grapes, managing the microclimate can become difficult, because the canopies are too close to each other, usually only about half a meter wide, or three-quarters of a meter.

“In Australia, we grow huge canopies because we've got water and we have soil temperature, alongside strong roots into good soil, making the huge hedge running down the rows very conducive to spreading the disease.

“Powdery mildew is killed off by UV light, and the more ultraviolet light you can get into the inner parts of the canopy, the better, because the humidity is higher when the canopy closes over and the UV kills the spores. 

“It is a narrow space, so you don’t get sunlight in, and air flow is restricted, which creates a good condition for downy mildew to grow.

“This is done because we need heat protection, but it can disrupt disease management.”

“On one hand, we want to increase the airflow between the canopies, but on the other hand we need shading. You can't have shading without reduced airflow."

Mr Magarey said that soil can be an issue, depending on what type of disease is more prone to grow in a specific type of crop.

“Let's take for example, phytophthora on almonds, it can be devastating, but the question is, how does it become devastating?” Mr Magarey said. 

“With phytophthora, the levels of the disease in the soil are really important, and they need to be measured, but also the controlling factor may be not whether or not the disease is in the soil or the organisms in the soil, but whether the conditions are right for the disease to spread.

“Soil health is an issue, but it is soil management in the context of irrigation, meaning how often the disease was moist or wet, having not let the soil dry out by controlling my irrigation timing.

“If growers know their irrigation timing, they can control moisture and have drier periods, or create a wet period, it can be a thin line.”

“If we go back in history, Australia lost almost $80m in the 1980s due to diseases and lack of soil management, but in the recent years, that number has been reduced to around $2m per year on average. 

“Growers have learned that they must control where and when they spray their crops, in order to manage the canopies and managing disease control by knowing the weather conditions.

“That is where GrowCare made a change in the Australian farming industry. We didn’t change the weather, we just got organised and started monitoring it.”

GrowCare still continues to provide valuable information about the current and historic weather conditions across stations all over Australia, by monitoring data such as moisture, rainfall, and droplets.

“The disease simulator we built in the 1980s was not adopted by other regions, but this approach was adopted by the Riverland,” Mr Magarey said.

“Within this system, there is a disease simulator, which can model downy mildew based off data collected around the network of weather stations around the area.

“They now automatically download the data, process it about every half hour, sometimes a couple of hours depending on the season.

“Back then, we had to type the information, but now everything is automated. The information is automatically stored and processed, and a disease risk statement and alert are sent out within two minutes of it occurring in a vineyard. 

“That alert arrives at your phone, and it’s up to the grower to decide if there is a need to spray, whether a downy mildew or an infection condition has been met." 

Mr Magarey said that controlling diseases is a matter of prevention rather than reaction, being the sooner you act on a possible infection, the long-term financial benefits will be greater. 

“It’s a bushfire analogy, but if you can kick the disease and stop it right from the beginning with your foot, then you stop the whole disease happening,” Mr Magarey said.

“If growers act when the disease has just been detected and it hasn’t spread, it can be controlled and eradicated. 

“If you wait until other conditions are met, or perhaps want to wait because of financial reasons, the outcome can become difficult if the disease has the right conditions to spread fast around a vineyard.

“Based on applying the right chemicals when you need them and the right timing, is the minimalistic approach, but can be the right one.”