Choosing the Right Pesticide: Modes of Action Matter

Pesticides control pests by interfering with essential biological or physical processes. While herbicides, insecticides, and fungicides are designed for different targets, each group includes products that work through direct contact, movement within the plant or pest, or disruption of growth and reproduction. Understanding these modes of action helps applicators choose the correct product, apply it effectively, and manage resistance.

Herbicide

• Pre-emergent: A pre-emergent herbicide is a weed control product designed to prevent weeds from growing by stopping seeds from germinating or emerging through the soil surface. Applied before weeds become visible, pre-emergent herbicides create a protective barrier in the top layer of soil that disrupts early root and shoot development. They are commonly used in crop fields, lawns, gardens, and landscaped areas to control annual grasses and broadleaf weeds before they can compete for water, nutrients, and sunlight, making them an essential tool for proactive, season-long weed management.
• Post-emergent: A post-emergent herbicide is a weed control product designed to kill weeds after they have already sprouted and are actively growing above the soil surface. Unlike pre-emergent herbicides that prevent weed seeds from germinating, post-emergent formulas target visible weeds by either contacting the foliage or moving systemically through the plant to destroy it down to the root. These herbicides are commonly used in agriculture, lawns, pastures, and non-crop areas to eliminate grassy and broadleaf weeds that compete for nutrients, water, and sunlight, helping protect crop yields and maintain clean, healthy landscapes.

Insecticide

• Contact (non-systemic): These products kill insects through direct contact by blocking breathing openings or disrupting the insect’s outer protective layer. They require thorough coverage to be effective and generally have little to no residual activity. Because their action is physical rather than biochemical, resistance development is less likely.
• Systemic and Ingested: These insecticides penetrate the insect’s body or are absorbed into plant tissue and ingested during feeding. They can reach insects that are hidden or feeding internally and often provide longer-lasting control. Because they target specific biological systems, careful rotation is important to prevent resistance.

Fungicide

• Protectant: These fungicides remain on the plant surface and prevent fungal spores from germinating or penetrating plant tissue, such as Manzate Pro-Stick or Nordox Copper. They must be applied before infection occurs and require complete coverage of all sides of the leaves and trunk. Reapplication is often needed as plants grow or after rainfall.
• Systemic: A systemic fungicide is a disease-control product that is absorbed by a plant and transported internally through its tissues to protect against fungal infections. Unlike contact fungicides that depend on good spray coverage for effective control of diseases, systemic fungicides move within the plant’s vascular system, allowing them to protect plant tissues even on untreated sides of the leaf or fruit. Systemic fungicides are best used as a preventive spray before a fungal disease occurs.
• Eradicant: An eradicant fungicide is a disease-control product designed to eliminate fungal infections after they have already been established on or within a plant. Unlike purely preventative fungicides, eradicant fungicides – such as Stylet Oil - work by stopping fungal growth and destroying active spores and mycelium, helping to halt the spread of disease. They are commonly used in combination with a systemic fungicide as a resistance management tool. 

In conclusion, selecting the right pesticide involves more than simply identifying the pest - it requires understanding how the product works and when it will be most effective. By recognizing the different modes of action for herbicides, insecticides, and fungicides, applicators can choose products that target pests at the appropriate stage while maximizing control and minimizing unnecessary applications. Using pesticides correctly not only improves results but also helps reduce the risk of resistance, protect plant health, and promote more sustainable pest management practices.