Cereal rust of all kinds have been developing resistance to a range of fungicides including a number of DMI fungicides. This includes rusts effecting wheat (stem, rust and stripe), barley (leaf) and oats (Crown and stem). With resistance to fungicides increasing, there is a significant risk of ineffective control of rust into the future, potentially leading to lower yields or increased input prices to control rust using other fungicides.
However, likely for you, Agresol specialising in reducing pesticide applications by focusing on plant nutrition and microbiology. So in this article we will show you a number of methods to reduce rust infections and severity without fungicide applications. This follows the principles of integrated disease management including incorporating biological, nutritional, genetic, and cultural control methods.
But first check out our video on our YouTube channel (Agriculture Explained), and make sure to subcribe!
What is Cereal Rust?
Cereal rusts are a group of plant diseases being caused by the pathogen Puccinia spp. These are air-born fungal pathogens, that once a spore lands on the plant’s leaf, germinates to release enzymes to break down the cell walls allowing for penetration into the plant. Once in the plant, the pathogen will start feeding on the plant. The most significant impact of rust is that it reduces the photosynthetic ability of the plant which reduces it’s ability to produce and supply carbohydrates into the grain, leading to a decrease in grain size and quality and, most importantly, yield!
Cereal rust are most damaging under high humidity allowing for wet leaves, and moderate temperatures, and high planting densities with poor airflow can increase the risk of infection.
The Basics
The basics of controlling cereal rust using an integrated disease management is standard, and include:
Genetic Resistance
Using resistant varieties can assist in withstanding rust pathogen infections.
Crop Rotation
Alternating crops to avoid planting the same crop continuously can reduce spore buildup.
Planting Densities
Ensuring proper spacing for your given yield targets to improve air circulation and reduce humidity around plants.
Removal of Alternative Hosts
The “green bridge” is a term used for plants that act as alternative host for rust out of the growing season, hence allowing for rust to re-infect crops. Typically the green bridge occurs along fence lines, around silos or any other areas. Grazing or use of chemical controls can be used to reduce rust build up in those areas.
Monitoring
As with all good integrated disease management, rust needs to be monitored to ensure timely control methods and estimates on when the disease will exceed economic thresholds.
Chemical Control
As a reactive control method, once the economic threshold has been reached meaning that the loss of income exceeds the cost to apply a chemical control, a chemical control should be considered. There’s a range of fungicides on the market suitable for controlling rust. Fungicides shouldn’t be the first means of control but is useful even for regenerative systems. Later we’ll discuss how we can reduce the negative effects of fungicides using humic substances.
Regenerative Control Methods
In addition to the basics, regenerative control methods aim to work with the plant’s immune system and natural systems to prevent the disease for ever reaching the economic threshold. Often these methods can be both proactively and reactively to allow for significant control of the disease. So in addition to the basic integrated disease management for rust we would consider the following.
Applications of Trichoderma spp.
Trichoderma is a genus of beneficial fungi widely used in agriculture for its ability to suppress plant pathogens, enhance plant growth, and improve soil health. These fungi are natural antagonists of many plant pathogens, including rust fungi.
Trichoderma can assist in controlling rust through a number of different ways including:
- Production of enzymes that break down the cell walls of pathogen fungi.
- Completes for nutrients and space.
- Production of secondary metabolites that inhibit the growth of pathogens.
Additionally, Trichoderma has been found to stimulate root development allowing for increased nutrient uptake, and stimulating induced systemic resistance in plants.
When working with clients we recommend to apply Trichoderma as a seed treatment instead of fungicide seed treatments. This helps to preserve the seed’s beneficial fungi community and provides protection for the plant’s whole life rather then the 4-6 weeks of protection from many fungicide seed treatments.
Additionally, Trichoderma can be applied as a foliar spray or in furrow as a liquid inject as a proactive and reactive control method for rust. The great benefit of Trichoderma is that it has an impact on a board range of plant pathogens, allowing for multiple pathogens to be controlled with one method.
Trichoderma has been well researched and in many studies (and this one) the application of Trichoderma was just as effective at controlling rust than the comparable fungicide, and with similar yields.
Pesticides often result in a yield loss as photosynthesis is reduced and proteins are denatured in order to detox the pesticides.
Application of Mycorrhizal Fungi
Although Mycorrhizal fungi don’t directly kill rust pathogen, there are a number of ways mycorrhizal fungi assist plants in defending against rust pathogens. This specifically relates to increased nutrient uptake (which we will discuss soon), and triggering plant immune systems.
In this study, Mycorrhizal Fungi was found to individually assist in the control of rust but also work synergically with Trichoderma to control rust to a greater degree than either working individually.
Mycorrhizal fungi would be best applied as a seed treatment for direct colonisation, and farmers should aim to use no-till practices, reduce fungicides, reduce high analysis fertilisers and maintain living roots all year long.
Applications of Bacillus subtilis
Bacillus subtilis is a bacteria found in soil and in plant rhizospheres. The bacteria has been found to promote a range of plant and soil health properties such as the production of phytohormones like auxin and gibberellins, and increase nutrient availability. However, Bacillus subtilis, has also been found to produce significant protection against rust pathogens.
This study, shows that the application of Bacillus subtilis, reduce rust by 65.6% while the fungicide propiconazole, reduced rust by 55.0%. In this study Bacillus subtilis outperformed the fungicide alternative and likely resulted in an increased yield and environmental benefits, while also protecting the plant against other pathogens.
It’s suggested that Bacillus subtilis protects the plant through the production of antifungal metabolites including lipopeptides and enzymes, as well as through the competition for resources and stimulating induced systemic resistance.
Like Trichoderma spp. , Bacillus subtilis can be applied as a seed treatments, foliar spray and soil inoculate.
Increasing Plant Health to Increased Lipid Production
When we start working with farmers, one of our farms is to rapidly increase plant health to start increasing lipid production. As seen in John Kempf’s Plant Health Pyramid, plant when supplied with the correct nutrition, increase their lipid production. This increases the waxy cuticle thickness helping to reduce rust fungi penetration into the leaf.
We’ve linked our video about John kempf’s Plant Health Pyramid below:
Strengthen the Cell Wall
Similar to above, we can prevent the entry of the rust pathogen into the cell wall by strengthening the cell wall with three key minerals, they are:
- Calcium
- Silicon
- Boron
We have produced a full video about this on our YouTube Channel, that you can watch below:
The general summary of the video is that Calcium and Silicon both strength the cell wall, hence resisting rust penetration. Boron is important for nutrient transport, therefore when all three are applied, cell walls are quickly strengthened. These are best to be applied as foliar sprays for best efficiency.
Trace Mineral Applications
Many of the plants we see when working with farmers are deficient in a range of trace minerals are they frequency are missed in typical nutrition plans. Below are the key trace minerals that are best to be applied as a foliar spray in order to increase the plant’s resistance to rust as according to Huber’s Mineral Nutrition and Plant Disease:
Potassium
Potassium has been found to decrease rust in cereals. This has been suggested by the ability of potassium to reduce nitrogen contents in plants and enhance systemic acquired resistance.
Sulfur
Sulfur is required for sulfur induced resistance. This is a natural resistance of plants against fungal pathogens through triggering the stimulation of metabolic processes involving sulfur. This has been found to reduce stem rust in wheat.
Copper
Copper has been found to decrease stripe rust in wheat. This has been suggested by copper’s role in lignin production, which is used to strengthen cell walls, additionally copper may have a role as a fungicide. Copper is required as a cofactor for many plant enzymes required in plant defence, the production of antimicrobial compounds and general disease resistance.
Manganese
Manganese has been found to decrease leaf and stem rust in cereals. Manganese oxides (Mn4+) has been found to accumulate around the site of infection, this acts to inhibit growth, sporulation, replication, enzyme production and toxin production. Additionally, Manganese enhances the production of inhibitory products, plant defence and other defence reactions.
Boron
Boron has been found to decrease stripe rust in wheat with reference to having a slightly toxic effect on fungi, strengthening the cell wall by maintain calcium and silicon levels, and the production of phenols and lignin.
Chloride
Although not commonly needing to be applied due to the use of salt based fertilisers, Chloride has been found to be an important nutrient in decreasing rust in cereals.
Nickel
Rust fungi have been found to be sensitive to Nickel, and nickel applied to the soil have been used as a reactive and proactive activity against rust. Nickel inhibits the germination of rust spores.
Reduce Free Nitrogen In Plant Sap
A final nutritional strategy is to reduce the amount of free nitrogen in the plant sap by ensuring the plant has sufficient levels of Mg, S, Mo, Ni and B to convent the free nitrogen into complete proteins. This is because free nitrogen in the plant is a food source for rust pathogens. Therefore, when we are able to convert 100% of free nitrogen every 24hrs, our plants stop becoming food sources for rust pathogens. For more info check out John Kempf’s Plant Health Pyramid.
Using Humic Substances with Fungicide applications
Although, as we have discussed above, many nutritional and microbial applications are more effective than fungicides and have additional benefits, if you are feeling the need to apply a fungicide, add at 5%, humic or fulvic acid. These are organic compounds that assist the plant and microbes in detoxing and breaking down the fungicide. When fungicides are applied, beneficial fungi such as mycorrhizal fungi and Trichoderma are also killed meaning you are killing off microbes that help your plant. Additionally, the plant stops photosynthesising and starts to break down proteins, this can reduce yield, growth and make the plant more suspectable to other pest and disease. Therefore, applying some fulvic or humic acid can help plants and microbes come back sooner. Although this won’t completely remove the negative impacts of fungicides, it can still help to reduce the negative effects.
In conclusion
Using a combination of nutrition and microbes can assist in preventing the need for fungicides to be applied for the control of rust. Applying and maintaining Mycorrhizal fungi, Trichoderma spp, and Bacillus subtilis, can help to naturally control rust pathogens while also supporting plant growth. Additionally, supplying the correct nutrition can increase plant health to resist rust attacks.
We can help!
As you can tell, we specialise in using plant nutrition and microbes to protect plants against rust and all other pest and disease. If you would like to stop rust without fungicides while using a better system of agriculture, then get in contract with us for a FREE 30min consultation.
