How Useful are Seaweeds in Pest Management?

Today, almost everyone in agriculture and horticulture is familiar with the usefulness of seaweeds. At a time when reducing chemical inputs and promoting organic and natural farming is a priority, the role of seaweeds becomes even more important. However, only a few people are aware of their correct application and their role in pest management. Let us understand this in detail.

What are Seaweeds and Why are They Useful?

Seaweeds are multicellular organisms that appear in different forms and colors. They are mainly found as red (Rhodophyta), brown (Phaeophyceae), and green (Chlorophyta) algae in both saline and freshwater environments. Their uniqueness lies in being rich in nutrients and bioactive compounds. This quality makes them a valuable resource for agriculture and horticulture. In farming, their extracts are commonly used. Since they are non-toxic, they are considered an eco-friendly alternative to chemical fertilizers.

What are Seaweeds Rich in?

Speaking with The Better Farming, Prof. S.K. Singh, Senior Scientist and Head, Department of Plant Pathology and Nematology, Dr. Rajendra Prasad Central Agricultural University, Pusa, Samastipur, Bihar, explained that seaweeds are rich in growth-promoting hormones such as auxins, cytokinins, kinetin, zeatin, and gibberellins. Their application enhances seed germination, crop vigor, and yield. At the same time, they help plants develop tolerance against various biotic and abiotic stresses. Brown seaweed extracts contain pigments like phycoerythrin and phycocyanin, which stimulate crop growth. Application through foliar spray or soil drenching improves seed germination, root development, and overall plant strength.

Nutritional and Bioactive Properties of Seaweeds

Seaweeds are rich in vitamins (A, C, E, B12), minerals (including iodine, calcium, magnesium, potassium, and iron), proteins, and essential fatty acids. They also contain alginates, carrageenan, and polysaccharides. In addition, bioactive compounds such as phytohormones, phenolics, flavonoids, and antioxidants make them effective biostimulants in agriculture.

A Proven Solution for Soil Health Improvement

According to Prof. Singh, seaweed extracts significantly improve soil structure and fertility. The organic matter and minerals in seaweeds enhance soil aeration, moisture retention, and microbial activity—all of which are crucial for healthy crop growth. Alginates present in seaweeds act as natural soil conditioners, improving water-holding capacity and making soil more porous and suitable for root development.

Seaweeds Promote Plant Growth

Seaweed extracts contain natural plant growth regulators such as auxins, cytokinins, and gibberellins. These promote root and shoot development as well as flowering and fruit setting. They stimulate cell division and elongation, leading to stronger plant growth. For example, the application of seaweed extracts increases root biomass, which improves nutrient uptake and stress tolerance.

Stress Resistance in Plants through Seaweeds

Prof. Singh points out that seaweed extracts enhance plant tolerance against abiotic stresses such as drought, salinity, and extreme temperatures. Antioxidants and stress-responsive molecules present in seaweeds help neutralize reactive oxygen species (ROS) generated under stress, thereby protecting plant cells from damage. This makes seaweed extracts especially valuable in maintaining crop yield and quality under challenging environmental conditions.

Nutrient Supply through Seaweeds

In horticultural crops, seaweed application provides an additional source of essential nutrients. The minerals and trace elements in seaweeds are available in forms easily absorbed by plants. For example, potassium improves fruit quality, while calcium strengthens cell walls and reduces disease incidence. Seaweed extracts also act as natural chelating agents, enhancing the availability of micronutrients in the soil.

Contribution to Higher Yields

Polysaccharides and other bioactive compounds in seaweeds contribute to better nutrient utilization and overall plant vigor. As a result, farmers benefit from higher productivity, along with extended shelf life of harvested produce.

Biocontrol Properties of Seaweeds

According to Prof. Singh, seaweeds also possess biocontrol properties that help in pest and disease management.
For example, a study on tomato and chili crops treated with Ascophyllum nodosum (a type of seaweed) showed improved plant health and significant reduction in pathogen intensity. Further studies revealed that up-regulation of defense-related enzymes reduced the severity of pathogens such as Xanthomonas campestris pv. vesicatoria and Alternaria solani.
Another study found that Ascophyllum nodosum treatment positively influenced maize rhizosphere microbial community. Similarly, in carrot crops, treatment reduced fungal diseases caused by Alternaria radicina and Botrytis cinerea. Compared with untreated plants, disease severity was lower 10–20 days after inoculation, and the seaweed treatment was found to be more effective than salicylic acid, a known stress-protective compound.

How to Use Seaweeds

1. Foliar Spray – Seaweed extracts are commonly applied as foliar sprays. Nutrients and growth regulators are absorbed directly through leaves, showing quick results on plant growth and development.
2. Soil Drenching – Seaweed extracts can be applied to the soil to improve fertility and structure. This method is particularly effective for root development and microbial activity.
3. Seed Treatment – Treating seeds with seaweed extracts before sowing improves germination rate and seedling vigor. Bioactive compounds in seaweeds support early root growth, making plants stronger and more resilient.
4. Compost Enrichment – Seaweeds can be added to compost, enriching organic matter with nutrients and bioactive compounds. This enriched compost helps improve soil health and plant growth.