Weed control in conventional and organic oats

As grass-weed herbicide options in oats are limited, it is especially important to use integrated pest management (IPM). Organic systems, with their focus on cultural control – use of rotation, stale seedbeds and mechanical weeding – provide valuable lessons for control in conventional crops.

How to manage weeds in arable rotations

Use the rotation to reduce weed burdens

Winter vs spring oats

Usually harvested after barley but before wheat, winter oats fit into the rotation well. They can also increase following wheat yields (by up to 15%) due to take-all reductions. However, winter oats can struggle in fields with large grass-weed populations, especially if herbicide resistance is present.

Spring oats add flexibility to the rotation. The spring-crop yield penalty is also relatively small in oats, compared with the penalty in wheat and barley. Additionally, spring oats provide an opportunity to use a long stale seedbed, as part of a black-grass control strategy. However, in some areas, ground conditions may not allow regular spring sowing.

Varietal choice

Whether organic or conventionally grown, varietal choice makes a difference to weed management. Generally, taller varieties are better at out-competing weeds. However, some modern shorter varieties have growth habits that help them supress weeds. Husked oats are also more competitive than naked-oat varieties.

Diverse rotations

In organic systems, more diverse rotations – including leys – help reduce weed burdens. During any ley phase, when legumes (typically grass/clover mixes) are grown, many weeds, such as creeping thistles and docks, can be controlled by mowing/topping before flowering. For localised areas, weeds can by removed by hand. Turning over arable fields to grass is also a highly effective way to reduce black-grass burdens – as its seed is relatively short-lived.

How to make the most of grass leys in the arable rotation

Make the most of stale seedbeds

Delayed autumn drilling provides more opportunity to form a stale seedbed. Generally, winter oats can be sown up to mid-October without a yield penalty.

Achieving good and rapid establishment helps the crop to out-compete early weed growth. It always better to drill later into a good seedbed than early into a poor one. In addition, due to increased soil moisture, pre-emergence herbicides generally have better efficacy with later sowings.

The use of spring oats as part of a black-grass control programme is effective. However, seed-rates must be increased if weed burdens are high, to help the crop out-compete emerging black-grass.

How drilling date affects arable weed populations

Consider mechanical weeding options

Mechanical weeding is most effective if done early (November for winter oats) – before weeds establish. This is particularly true for black-grass. If the crop is strong enough to withstand it, use a spring-tine weeder to remove weeds. Depending on soil conditions, aim to achieve several passes before the onset of winter. After the crop begins to cover the inter-rows, use an inter-row hoe (if necessary) until the canopy nearly closes. Mechanical weeding may provide an extra benefit to the oat crop by mineralising nitrogen.

Chemical control options

Limited herbicides and resistance issues (in some populations) make weed control in oats a challenge. In addition, application rates and/or latest timing of herbicides may be different in oats, compared with other cereals.

Be aware that the use of certain pre-emergence products may restrict the choice of herbicides available post-emergence.

Always refer to the product label for specific usage restrictions and guidance (including tank-mixing and sequencing options).

The information on this page was last reviewed in 2016.

Plant protection product on-label approvals

Plant protection product EAMU (off-label) approvals

Pre-emergence herbicides

Pre–emergence products are classed as ‘Extension of Authorisation for minor use (EAMU)’ and most of these apply only to winter oats.

To optimise the activity, ensure seedbeds are fine, with adequate moisture, and well consolidated – with no large clods that could break open and prolonged weed flushes.

Be aware that the use of certain pre-emergence products may restrict the choice of herbicides available post-emergence.

Active ingredient

Broad-leaved weed control

Annual grass-weed control

Authorised in winter oats

Authorised in spring oats

Diflufenican

Yes

Yes

Yes

Yes

Diflufenican + flufenacet

Yes

Yes

Yes

 

Diflufenican +

flupyrsulfuron-methyl

Yes

Yes

Yes

 

Fumioxazine

 

Yes

Yes

 

Autumn post-emergence herbicides

Active ingredient

Broad-leaved weed control

Annual grass-weed control

Authorised in winter oats

Authorised in spring oats

Carfentrazone-ethyl

Yes

 

Yes

Yes

Carfentrazone-ethyl + flupyrsulfuron-methyl

Yes

Yes

Yes

 

Carfentrazone-ethyl +

mecoprop-P

Yes

 

Yes

Yes

Flupyrsulfuron-methyl

Yes

Yes

Yes

 

Flupyrsulfuron-methyl +

thifensulfuron-methyl

Yes

Yes

Yes

 

Isoxaben

Yes

 

Yes

Yes

Spring post-emergence herbicides

Spring herbicide options tend to target broad-leaved weeds. Compared with other cereals, tank-mixing options are limited and crop damage may occur.

Active ingredients

  • 2,4-D*
  • 2,4-DB
  • 2,4-D + MCPA*
  • Amidosulfuron
  • Bromoxynil
  • Bromoxynil + ioxynil
  • Clopyralid
  • Clopyralid + florasulam**
  • Clopyralid + florasulam + fluroxypyr
  • Dicamba + mecoprop-P
  • Dicamba + MCPA + mecoprop-P
  • Dichloprop-p + MCPA + mecoprop-p
  • Florasulam
  • Florasulam + fluroxypyr
  • Fluroxypyr
  • MCPA
  • Mecoprop-P
  • Metsulfuron-methyl
  • Metsulfuron-methyl + thifensulfuron-methyl*
  • Metsulfuron-methyl + tribenuron-methyl
  • Thifensulfuron-methyl + tribenuron-methyl*
  • Tribenuron-methyl

*Authorised in winter oats only

**Authorised in spring oats only

Pre-harvest herbicides

Glyphosate can be used pre-harvest on oats to control perennial weeds and to even up ripening for ease of harvesting.

Pre-harvest glyphosate: best practice in cereals



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