You are here

Managing weeds in lucerne

Forage
24.04.2019
Managing weeds in lucerne crops

Grass and broadleaf weeds are a serious threat to the quality and viability of a lucerne stand.  Weeds can reduce the nutritional value of the crop and cause significant reduction in yield as they compete aggressively for water, nutrients, sunlight, and space.

The grazing or cutting of lucerne encourages weed growth.  Failing to control weeds will result in poor crop performance, and can shorten the productive life of a lucerne stand by many years. 

GRAMOXONE® (plus atrazine) provides excellent knockdown and residual control of a wide range of grass and broadleaf weeds.  Applied to lucerne annually during winter when the crop is dormant, GRAMOXONE (plus atrazine) can increase lucerne yields by up to 30%, and extend the productive life of a stand by many years.

GRAMOXONE is a non-residual, fast acting, contact herbicide containing 250 g/litre paraquat in the form of a soluble concentrate.  Most grasses and broadleaf weeds are controlled by GRAMOXONE, although clovers recover quickly.  It is inactivated on contact with the soil. GRAMOXONE contains a blue dye for identification, and a stenching agent to reduce the risk of accidental ingestion.

GRAMOXONE (plus atrazine) should be applied to established lucerne (older than 12 months) during dormancy (i.e. winter months) after the crop has been hard grazed or cut, before the onset of spring growth.

Sunlight triggers the activation of GRAMOXONE.  Under bright/sunny conditions GRAMOXONE starts working almost immediately, resulting in a quicker kill.  However, dull/cloudy conditions allow greater uptake of GRAMOXONE before it starts to work, resulting in slightly slower, but equal or better, weed control.

Do NOT spray GRAMOXONE when frost is on foliage, or under excessively wet soil conditions.  Also, do NOT spray GRAMOXONE when the foliage of weeds is dirty, as this will inactivate the herbicide and give poor results.

GRAMOXONE should be applied via normal ground application equipment.  Good spray coverage of weeds is essential for best results.  Water rates of 250-300 litres/ha are recommended using clean water, as dirty water will inactivate the GRAMOXONE. The addition of a non-ionic wetting agent can improve coverage and reduce run-off.

In late autumn (May/June) let lucerne crops flower, allowing root reserves to replenish before close grazing or cutting the crop to remove all foliage.  It is important that the foliage is removed to allow thorough spray coverage of weeds.  Allow weeds to freshen up for 7-14 days before spraying.

Experience has shown that 2.4 litres/ha GRAMOXONE provides the most consistent performance in all situations.  Lower use rates (as specified on the GRAMOXONE label) should NOT be used if weeds have passed the two leaf stage.

The addition of atrazine to GRAMOXONE is highly recommended.  Atrazine is a ‘photosynthetic inhibitor’ herbicide (opposite action to GRAMOXONE).  Atrazine promotes greater uptake of GRAMOXONE by slowing its destruction of plant cells, resulting in improved control of larger and harder to control weed species.

For couch, paspalum and kikuyu control, use a specific graminicide (grass killer) such as FUSILADE®.  For established rhizomatous or deep tap-rooted weeds (e.g. Californian thistle, dandelion, docks, hawkesbeard), seek advice from your merchant or local Syngenta representative.

Wettable Granule (WG) formulations of atrazine are recommended over liquids (SC/FW) for tank mix compatibility.  When mixing with atrazine 90% WG, add atrazine granules before adding GRAMOXONE and agitate well.

Agitate mixture throughout spraying.  Aim for medium to coarse spray droplets in sufficient water to achieve thorough coverage. The use of angled Syngenta DEFY 3D nozzles will help to improve spray coverage and can reduce spray drift by up to 50% compared to conventional flat fan nozzles.

Best use advice for GRAMOXONE in lucerne

  • Remove all lucerne growth by hard grazing or close cutting before use.
  • Allow weeds to freshen up before application.
  • Apply 2.4 litres/ha of GRAMOXONE during lucerne dormancy.
  • Add 1 kg/ha atrazine (90% WG) on stands older than 12 months.
  • Apply only to clean, healthy weed foliage.
  • Avoid spraying when frost is on foliage.
  • Ensure total coverage of weeds.
  • Use only clean water.

Click here to download the Technote on how to increase lucerne yields with effective weed control.