Snapshot

Crop protection chemicals such as herbicides have made no-till farming a viable option, allowing farmers to reduce erosion by leaving the soil largely undisturbed. Herbicides can be utilised for controlling weeds in no-till crop production, removing the need for cultivation; residue from the previous crop holds the soil in place during wind and rain. Crop residue also prevents runoff of agricultural chemicals and soil that may otherwise impact aquatic habitat and fresh water supplies downstream.

Herbicides are used to control the growth of unwanted plants (weeds). Modern herbicides generally act by restricting growth. They inhibit the action of one or more of the many receptors that catalyze reactions which are essential to the growth of the plant. There is one group however, the auxins, that kill by overstimulating growth. With selective herbicides, either the target in the weed is affected more than that of the crop, the herbicide is degraded more quickly within the crop, or the uptake or translocation of the active ingredient differs from that of weeds. Non-selective herbicides kill crops as well as weeds.

Herbicides can act in several ways:

direct contact with plant tissues, for example, leaves; paraquat is a typical contact herbicide

• by translocation (systemic herbicides),whereby the compound has the ability to be absorbed by aerial plant parts and is transported to roots (basipetal translocation); glyphosate and growth hormones belong to this group

• by root uptake and transportation, to the upper parts of the plant (acropetal translocation)

• through a combination of both methods; triketones are an example of this group as they are transported downwards and upwards

Modern herbicides are often synthetic mimics of natural plant hormones which interfere with growth of the target plants. The term organic herbicide has come to mean herbicides intended for organic farming. Some plants also produce their own natural herbicides, such as the genus Juglans (walnuts), or the tree of heaven; such action of natural herbicides, and other related chemical interactions, is called allelopathy. Due to herbicide resistance – a major concern in agriculture – a number of products combine herbicides with different means of action. Integrated pest management may use herbicides alongside other pest control methods.