Nurturing nature – Part 2: how can I use holistic growing practices?

Holistic disease management approach
By the time you’ve noticed disease in your crop, you have already paid a price in terms of yield – and there’ll be another cost in the form of an expensive curative product. We’ve built our holistic approach around aiming to avoid infections completely, helping plants to grow at their optimum while keeping input costs low.

Growing media
A holistic growing strategy must begin with selecting the right growing media – healthy growth relies on correct nutrition; for this, a strong root zone is essential. The media needs a suitable physical structure for the growth of your selected crop (fine mixes for smaller crops and coarser mixes for larger ones) to enable sufficient water delivery and to have good porosity for root oxygen uptake. Also, it needs to be able to hold and deliver nutrients and provide suitable ecological niches to encourage beneficial microbes.

Fertilisation
Plants have a wide variety of strategies for handling pathogen attacks, giving them a high level of natural protection. But an improperly fed plant is unable to undertake these processes, leaving it vulnerable – so, to help the plant manage disease, it is vital to get your nutrition correct.

Importance of organic fertilisation
In a holistic growing system, you must consider both the fertilisation of the plant, as well as fertilisation of the microbes around the roots. By doing this you foster a healthy rhizosphere microbiome, which delivers a range of benefits to plant health – including excluding and combating pathogens as well as inducing the plant’s natural resistance.

It is possible to feed both the plant and beneficial microbes simultaneously via the use of organic nutrition. The microbes in an organic fertiliser have evolved from natural systems where degrading organic matter feeds them, during which they release nutrients in mineral form that the plant takes up. So, by integrating organic nutrition (such as the DCM product range) into the pot or by top-dressing around the plant, we can simulate this system.

Using only mineral fertilisers, where the nutrients are provided in soluble form ready for plant uptake, bypasses the beneficial microbes. As they are not nourished, the population of these beneficial microbes declines. Without a thriving root zone microbiome, the plant does not gain any of the benefits of these microbes, leaving a vacuum that pathogens exploit.

Considerations with Mineral Fertilisation
While we aim to mimic natural systems to capitalise on the benefits of these ecological relationships, the demands we place on crops is unnatural. As such, mineral fertilisation is very useful for driving plant growth and, if used in partnership with organic feed, we can deliver growth at an optimum level.

But, using only mineral fertilisation is rarely ideal for delivering optimal plant nutrition, as it can be difficult to align the nutrient availability with plant demands. Plants adjust their growth and development based on the recent availability of water, light, nutrition and heat. So, we need to ensure a consistent supply of nutrition, delivered in correct volumes to suit environmental conditions, allowing the plant to allocate its resources effectively for strong and steady growth.

Liquid mineral feeds
In the case of liquid feeds, nutrients are generally not retained well by the growing media, especially in peat-free mixes with lower cation exchange capacity. This means the nutrients are initially very available, but quickly diminish. If there are large gaps between applications, the plant finds itself in a situation of feast or famine – swinging between too much nutrition to use and too little.

To manage this, we recommend using a granular organic fertiliser to ensure a slow and constant supply of nutrition and then, when faster growth is needed, supplement this with low levels of liquid feed at every watering. This should ensure that there is always steady availability of nutrition in the pot. 

Granular mineral feeds
In the case of granular mineral feeds, aligning nutrient release with plant demand is challenging as plant metabolism follows a biological pattern, rather than chemical one.

For granular mineral feeds, release is directly mediated by temperature – the higher the temperature, the faster the release. This works well in good growing conditions but is less than ideal during more extreme conditions seen in winter and during the height of summer. Plants still require a small amount of nutrition at lower temperatures, which often isn’t supplied because it is too cold for mineral release – which limits root development over winter. 

At very high temperatures, plants become dormant and stop taking up nutrients, but granular mineral feeds release even faster. This is a problem as it leads to a nutrient build-up in the pot, and so, when the plant becomes active again, there is an excess of nutrition, causing imbalances that impact crop development and make the plant vulnerable to foliar diseases. In addition, high nutrient levels increase salinity, which causes root burn, providing an entry point for root pathogens.  

But, organic granules rely on rhizosphere microbes to mineralise nutrition, which means microbial metabolic activity determines the speed of release. This activity is closely aligned with the plant’s behaviour. This means that organic feeds can effectively deliver the small amount of feed required in lower temperatures, provide a large amount during ideal growing conditions, and won’t release excess nutrition at very high temperatures when plants go dormant.

But, organic granules cannot match the longevity of granular mineral feeds – often only lasting for 150 days at most. So, a late-releasing and longer-lasting granular mineral feed can be an excellent accompaniment to organics. This works by allowing the organic feed to establish a strong initial root system capable of using larger volumes of nutrients released by the mineral granules. This not only improves the speed of growth, but also means the mature roots are more resilient against any irregular release patterns.

Importance of nitrogen management
Being the most in-demand plant nutrient, fertilisation programmes require high levels of nitrogen to ensure growth. But, overfeeding nitrogen presents a number of severe challenges to plants.

Firstly, an excess of nitrogen disrupts important plant processes, especially those related to natural pathogen defences and maintaining a healthy microbiome. This creates a need for expensive applications of pesticides and plant growth regulators. 

When plants take up nitrogen, the nitrogen is converted into amino acids then transported in the sap to the foliage and used in protein production. These amino acids are the food source for many foliar pathogens, such as powdery mildew. In a balanced plant, the production of amino acids aligns to their use – keeping their availability low in the sap, which deprives the pathogens of a food source. But, when overfed with nitrogen, the supply of amino acids exceeds their consumption, leading to a build-up of nutrients increasing the chances of infection.

Holistic fertilisation strategy
To achieve optimal plant nutrition, we recommend using granular organic feed as the main source of nutrition, then make highly targeted applications of liquid or granular feed to supplement this. Be mindful that not all organic feeds are the same, so it is important to select a sophisticated product (such as DCM) so that you know what the nutritional content and release profile are. 

Rhizosphere beneficial microbe management
Now you’ve created an ideal environment for establishment of beneficial microbes, it’s important to think about their introduction to ensure establishment around the root zone.

There are various types of beneficials – free-living plant growth promoting rhizobacteria (PGPR), root-protecting Trichoderma fungi (such as that found in T34), or nutrient-foraging mycorrhizal fungi.

A diverse community is required for the plant to flourish, so it’s key to involve different microbes – which have often evolved to act synergistically. To do this, consider using products that contain these microbes, or ask your growing media manufacturer to include composted materials in your mix – which will already host a microbial community. 

A well-nourished plant forms relationships with these microbes, feeding them by releasing sugars and metabolites. In return, the microbes help to suppress root pathogens.

Phyllosphere beneficial microbe management
Plants also have microbiomes on their above-ground parts – this is known as the phyllosphere.

Just like the roots, fertilisation is key to sustain a healthy phyllosphere microbiome. Plants can recruit and retain beneficial phyllosphere microbes and provide a strong, healthy leaf surface for them to establish on. This acts as a highly effective physical and biological barrier against pathogen attacks.

But, we don’t want to rely on chance to build this community. Instead, we want to ensure that the community contains microbes that perform desired functions. This can be achieved through targeted applications of biopesticides that contain these microbes.

Products like Taegro contain the bacteria Bacillus amyloliquefaciens which can establish on the leaf, inducing systemic resistance in the plant and secrete anti-fungal compounds to protect from a wide range of pathogens.

If your crop is particularly susceptible to powdery mildew, AQ10 could be very useful. It contains the fungus Ampelomyces quisqualis, which is a parasite of powdery mildew. Understanding the active microbe in the product will allow you to select effectively the correct microbes to protect your plant from disease.

Plant processes can also be manipulated in our favour. One of the most effective methods is by using a plant defence elicitor. Romeo, which contains a purified extract of brewers yeast, is an exceptionally effective product. It simulates a pathogen attack which causes the plant to upregulate its natural defences – meaning that it will stimulate the processes that recruit and retain beneficial microbes.

The correct elicitor allows a grower to maximise the efficacy of biopesticide applications and prolong the length of the control delivered.

Risks of chemical fungicide applications
Chemical fungicides are an important tool in the armoury of growers in case of a severe disease outbreak. 

But their use can also have negative impacts on the plant and on beneficial microbes present in the phyllosphere and rhizosphere.

Many conventional fungicides will have a temporary influence on plant activity, slowing or stopping protein synthesis and growth. This can lead to a build-up of amino acids in the sap that act as a food source for many pathogens. So, the initial infection could be cured, but susceptibility to a new pathogen could be increased after application.

It’s also important to understand that these products are often not selective between beneficial and pathogenic microbes. A fungicide application will not only kill the pathogenic fungi, but also kill the beneficial fungi that are providing protection to the plant. In addition, many fungicides also have a negative impact on bacteria, meaning that even though you may have successfully removed the target pathogens, you’ll likely disrupt any community of beneficial microbes. This can actually create a vacuum that can be exploited by pathogens. 

So, it is vital to use only chemical fungicides as a last resort against established infections. After use, it is crucial to restore your friendly microbial community, reintroducing beneficial microbes.

By following holistic growing methods, you should be able to avoid or severely restrict chemical use.

Holistic Plant Protection Product use strategy
When implementing a holistic growing strategy, plant protection products must be used in a preventative programme alongside a well-devised fertilisation programme. This should help prevent infections occurring and minimise damage to the crop, and support strong crop development.

Ideally, all active ingredients should be biological, as these products can strengthen the plant. The correct products (such as beneficial microbes and elicitors) can work synergistically to provide much higher levels of control than when used individually.

For root diseases, an initial application of microbes should suffice, provided the growing media environment supports their development. But, follow-up applications can be helpful after a month or so.

For foliar diseases, we recommend spraying regularly (each week or each fortnight) depending on disease pressure.

By Jack Haslam, Fargro technical development manager