Farmers have been warned to be aware of the “trade-off” between sowing winter crops now and the reduced pressure of grass weeds and Barley Yellow Dwarf Virus (BYDV) that delayed sowing brings.

Ciaran Collins, Teagasc tillage specialist, said conditions are currently positive for getting winter crops sown with soil temperatures between 1°C and 2°C above normal.

Collins said this would indicate that speed of emergence would be quick for crops that are being sown currently.

“This also means that grass weed pressure will be higher for these crops when compared to crops sown in the latter half of October.

“All farmers are aware of the increasing difficulty in controlling grass weeds and this difficulty increases where resistant weeds are present.”

Vijaya Bhaskar a researcher with Teagasc has also confirmed that there is resistance to some commonly used post emergence herbicides.

The authority is therefore advising that growers should be cautious when it comes to planning grass weed control in winter wheat and barley.

Teagasc states that populations of Blackgrass and Italian ryegrass are resistant to the post-emergence ALS herbicides: Pacifica and Broadway Star.

Reduced sensitivity has also been detected in brome species to Pacifica, although brome can be well controlled by Broadway Star.

But Teagasc has warned that a resistant population of annual meadow grass to Pacifica has been detected and advised that Broadway Star does not control annual meadow grass.  

The authority has recommended that a pre-emergence herbicide should give growers the best chance of controlling difficult grass weeds.

The key active ingredients to consider include flufenacet (component of Firebird), prosulfocarb (Defy) or pendimethalin (Stomp).

Collins added:

“These will give excellent control of annual meadow grass when used pre emergence in wheat and barley.

“This approach is particularly important in winter barley as post emergence application is less effective.”

For brome control in wheat, especially fields with high populations, Teagasc is advising a target pre-emergence application of flufenacet/pendimethalin followed by a post-emergence application in spring.

It has advised that barley should not be grown on land with high brome populations due to the limited post-emergence options available.

However, Teagasc has also suggested that flufenacet (pre emergence) will give some control although it has highlighted that this is far from a total solution.

It has indicated that in addition to better grass weed control, a pre emergence herbicide application also increases the broad-leaved weed spectrum and often results in lower cost weed control within cereal crops.