Silicon: a Biocontrol Agent that Boosts Plant Immunity
Quality and profitability are two important factors that drive our agricultural markets. We have fine-tuned our cultivation processes over centuries to obtain higher yields with lower inputs to protect both our environment and our bodies.
The biocontrol market contains a diverse set of less-toxic alternatives to aid in the overall goal of environmental stewardship. One set of materials contain a bioavailable form of silicon, important for enhancing the plant’s natural immune system.
Silicon is an essential trace element important for animal and human health. It also has an important role in plant health.
Silicon Protects Against Some Disease And Insect Pests
Studies show that adding silicon to the growing media significantly reduces the presence of powdery mildew in a variety of plants, including cucumber, tomatoes, strawberries, grapes, melons, and lettuce. This nutrient also protects against bacterial and viral infections in certain plants.
Not only does silicon protect against disease, it also reduces the population of insects and mites feeding on silicon-treated plants.
For many years, it was thought that silicon provided a physical barrier associated with the plant cuticle, making it harder for insects to penetrate.
While this process is involved, recent studies show that arthropods feeding on silicon-treated plants produce fewer offspring, suggesting that silicon is altering some aspect of the plant material ingested by these menaces. Combining silicon with other biocontrol agents may lead to better protection and control over infestations.
Tips on Gaining Nutrition from Silicon
There are many forms of silicon that can be taken up by plants.
Commercially available products include:
■ Solid materials for media incorporation that come from mined rocks (wollastonite and ignimbrite)
■ Recycled slag from the steel industry (also containing additional micronutrients and used as alternative liming agents)
■ Recycled glass (used as solid substrate in hydroponics or aquaponics)
■ Plant material (including rice hulls, coir, and biochar produced from plant material).
■ Liquid materials that can be applied as a media drench or foliar spray (including potassium-, sodium-, and calcium-silicates).
These materials have unique characteristics and release varying amounts of plant-available silicon. It is important to match the material with your growing system.
The amount of silicon required to enhance growth and stress resistance varies greatly by plant type and even variety. There are no current recommendations for silicon concentrations in plant tissue.
As a general rule of thumb, many of the grasses and grains need large amounts (and can take up to 100,000 ppm or higher silicon), while dicots range in their foliar concentrations from 10,000 ppm (in cucumber) to 100 ppm (in onion). It is important to note that silicon protects both cucumber and onion in various stress responses, showing that foliar concentration does not predict protection.
Silicon fits in as a biocontrol because it enhances the plant’s own immune response, allowing for a faster and more robust response to invading pathogens or herbivores. By providing plants with this nutrient prior to the onset of disease or early in the detection of nuisance arthropods, we can help our photosynthetic friends maintain their quality and yield, even in the presence of stress.