In some situations, the use of herbicides offers the only practical and selective method of managing certain weeds. Herbicidal applications are usually cost-effective control methods in bushland contexts, particularly when funding is scarce.
In many cases, a weed is only susceptible to one specific herbicide and it is important to use the correct product and application rate for control of that particular weed. Common mistakes include incorrect identification of the weed or using inappropriate products because they are the cheapest option. In most cases, weeds must be actively growing to be vulnerable to herbicide treatments.
There are five types of herbicides:
- Broad spectrum - these work on a wide variety of plants.
- Selective - these work on a narrow range of plants.
- Contact - these kill plant tissue at or near the point of contact with it (they do not spread around the plant). Therefore, they require even coverage in their application.
- Systemic - these move through the plant tissues via the plant's circulation system, and these can be injected into the plant.
- Residual - these can be applied to the soil in order to kill weeds by root uptake. They remain active in the ground for a certain length of time, and can control germinating seedlings.