Success takes planning: winter weed control in lucerne

Effective weed management is done through a combination of mowing, grazing, and spraying. Using a mower can remove annual weeds before they set seed.

Failing lucerne crops often boils down to a lost battle with weeds, especially perennial ones, which causes a marked decline in production and feed quality. Weeds win the battle for water, nutrients, and sunlight when crop growth becomes restricted and less competitive.

Paddock fertility has a major influence on lucerne production and longevity. Prioritising nutrition throughout the season is important as it allows for vigorous growth, enables competition, and prevents weeds from  establishing in the first place. An annual application of lime is essential to maintain pH levels, as is adding Potassium (K) at regular intervals,  particularly if the crop is cut and removed.

Weed control in lucerne can be divided into two camps: establishing phase (< 12-months) and mature crops ( > 12-months). During the establishment phase, it is critical to obtain as close to 100 percent weed control as possible. Weeds emerging with lucerne seedings can reduce density of the establishing crop, impacting potential yield from the outset.

Herbicides are always more effective when weeds are small, so applying a spray containing 2,4-DB or Imazethapyr (depending on the weeds you are targeting) at the second trifoliate leaf of the lucerne is an ideal way of giving emerging lucerne the best 

start. Flumetsulam containing herbicides can also be applied after the crop has achieved four trifoliate leaves. Continue to monitor your established crops during spring and summer for weeds, as there are selective herbicide options targeting specific weeds throughout the year including grass weeds.

Herbicide options for establishing crops are different than mature ones which is an important differentiation. The winter dormancy phase of lucerne is the right time to control weeds in mature crops. Identifying weeds and their numbers through paddock monitoring during late autumn will help with the selection of herbicides.

Mature lucerne weed control requires a mixture of a contact burn down spray (containing paraquat) and another residual herbicide (usually containing atrazine or flumioxazin). This results in a browning down of weeds and leaving a residual herbicide layer on the surface of the soil to kill emerging weeds. This can also remove older leaves that are a perfect environment for disease and aphids.

• Weeds reduce the yield quality and longevity of your Lucerne crop.
• Make sure the fertility of the soil is adequate and maintained, especially K and pH levels.
• Weed control split into two distinct periods with: establishment phase and mature crop.
• Herbicide options are different depending on the growth stage of the crop.
• Walk paddock for weeds in order to target herbicide product selection.
• Established crops make the most of a winter spray when the crop is  dormant.

For help planning effective weed management in lucerne, contact your local PGG Wrightson Technical Field Representative.