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Get your winter cereal weed control off to the best start with a pre emergence herbicide

Ciaran Collins, Teagasc Crops specialist tells us that sowing of winter wheat and barley is underway and as always there is the trade-off between getting crops sown in good conditions versus the reduced pressure of grass weeds and BYDV that delayed sowing brings.

Soil temperatures are still between 1 and 2°C above normal so speed of emergence will be quick for crops sown this week. 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. Teagasc researcher Vijaya Bhaskar has confirmed resistance to some commonly used post emergence herbicides so caution is advised when planning grass weed control in winter wheat and barley.

Populations of blackgrass and Italian Rye grass are resistant to post emergence ALS herbicides Pacifica and Broadway Star. Reduced sensitivity has been detected in brome species to Pacifica but brome is still well controlled by Broadway Star.

Worryingly a resistant population of annual meadow grass to Pacifica has been detected and Broadway star does not control annual meadow grass.  

Therefore using a pre emergence herbicide will give the grower the best chance of controlling difficult grass weeds. Key active ingredients include flufenacet (component of Firebird), prosulfocarb (Defy) or pendimethalin (Stomp).

All of 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 target pre-emergence application of flufenacet/pendimethalin followed by post emergence application in spring. Barley should not be grown on land with high brome populations due to the limited post emergence options available but Teagasc trails have shown that flufenacet (pre em) will give some control but this is far from a total solution.

In addition to better grass weed control, pre emergence herbicide application also increases the broad leaved weed spectrum and often results in lower cost weed control.

Find out more information and advice from the Teagasc Crops team here. Find your local Teagasc office here