Many gardeners grab the variety of herbicide sprays available when they notice that their gardens have weeds springing up. These weeds are considered unsightly to some gardeners and wastes of nutrients to other gardeners. The chemical herbicide option seems a lot easier and more effective than simply pulling the weed out.
Herbicides are designed to either kill weeds or prevent these weeds from growing fully. Dealing with weeds can be a complicated process because gardeners want to avoid damaging the plants that they like. The University of Rhode Island pointed out that, the types of herbicides, the amounts and the other weed control methods used in combination can vary.
Herbicides come in different types. Selective herbicides are designed to kill specific plants while not killing other plants. For instance, there are selective herbicides that are designed to kill weeds such as dandelions while not killing the turfgrass. Other kinds of herbicide are non-selective and have the ability to kill all plants. However, according to the University of Rhode Island, non-selective herbicides that are used in the right doses and applied in the right areas can serve as selective herbicides. Also, very large doses of selective herbicide will kill most plants.
Herbicides are also divided into categories of contact and systemic. Contact herbicides kill whatever part of the plant that the herbicide contacts with. The systemic herbicides are absorbed into the soil and kill the entire plant when the plant absorbs the herbicide through the soil.
Some herbicides mimic chemicals that are normally found within a particular plant. For instance, the phenoxy herbicide mimics the growth hormone found in broadleaf plants and interferes with this hormone. Other herbicides interfere with the ability of seeds to grow roots, preventing germination. Some herbicides are designed to interfere with photosynthesis.
Choosing which herbicide to use on harmful weeds will depend on whether the harmful weed is a biennial, perennial or an annual. Annual weeds have a life cycle that only lasts one year, with this weed surviving for only one year before reproducing. Biennial weeds are similar, but last for two years. The University of Tennessee explains that perennials, however, can be difficult to get rid of because these plants can keep returning every year. For annual and biennial weeds, herbicides that prevent new plants from germinating are the most effective. For perennial weeds, herbicide must be used that actually kills the weed.
Some weeds might develop a resistance to herbicides after being exposed to these herbicides after a couple of generations. This happens when a small selection of a weed species has a genetic mutation that gives those weeds characteristics that make them resistant to herbicides. These types of weeds become dominant when all of the other weeds are wiped out by herbicides.