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The importance of early weed control in pasture

The importance of early weed control in pasture

The importance of early weed control in pasture

Weeds cause significant yield losses in New Zealand pastures every year as they compete for light, moisture and nutrients. By controlling weeds early, the potential damage to pastures is greatly reduced.

Early control of weeds helps prevent bare areas forming in new pasture. The larger weeds grow, the bigger the gaps that appear after a control treatment is applied. These areas create room for new weeds to germinate and can cause issues for the following seasons.

Effective weed control supports the preferable pasture species tiller development and helps prevent weed seeds from establishing. For these reasons there is often a tendency to want to graze weeds out. The problem is that it is difficult to gauge the line between grazing hard enough that the growing point of the weed is removed, while not grazing the pasture species so hard that it is damaged early in its life.

Some perennial weeds, such as Californian thistle, docks and buttercups utilise bare land to establish themselves, setting them up to cause greater problems in years to come. The good news is they are not good at establishing within a competitive sward.

Californian thistle is commonly found on-farm and is one of the weeds that causes the most problems in terms of decision-making around when and how to spray due to its underground creeping root system. The best strategy for long-term control of California thistle is to stop it from establishing during the pasture’s early growth stages.

Removing weeds while they are small provides the opportunity to use softer chemistry. These products target specific weeds while not harming clover in the sward. MCPB/MCPA mixes, flumetsulam, bentazone, bentazone/MCPB mixes and flumetsulam/bentazone mixes are some common chemicals used depending on the weeds present in the pasture. As weeds become bigger, they become less susceptible to most of these options, so tougher chemicals need to be considered. Using these products may severely stunt clover growth, or at worst, kill it.

When chicory or plantain is present in a ryegrass and clover sward, the choice of weed control options decreases further and timing becomes critical. Even with the registered chemical options available for plantain, it will still be affected by the chemical. To help alleviate this outcome, applying the chemical as soon as is practicable provides the greatest opportunity to control weeds without impacting too much on the plantain in the sward.

For help developing an effective weed control programme, contact your local PGG Wrightson Technical Field Representative.