High levels of weeds in grass reduce its nutritional value (chickweed has low water-soluble carbohydrates), restrict grazing areas (animals won’t graze near thistles), restrict valuable grass growth (docks proportionally reduce silage yields) and can poison animals (ragwort). Farmers should be aware of their obligation to take action against certain weeds listed in the Noxious Weeds Act. This is important for cross compliance.

In normal circumstances, low levels of weeds in pasture are of no consequence and their removal may not be cost effective. Certain grassland weeds have high levels of trace elements and, also, have environmental benefits as food sources to birds, invertebrates and small mammals. However, when weeds take over 10% to 20% of a sward, weed control becomes important and warranted.