When do grass weeds emerge?

Knowing when grass weeds germinate and emerge is a key factor in knowing how to control those weeds and plan your crop rotation.

Grass weeds are becoming more difficult to control as resistance builds to chemistry and the chemical toolbox declines.

As a result, it is essential to make good use of cultural control strategies when it comes to grass weed control.

The impact of integrated pest management and cultural control techniques provides longer-term solutions and farmers should really only be looking at the chemical control options as a last resort.

The chart below is from Teagasc and it is evident from looking at the different grass weeds that the more problematic weeds germinate for longer periods of the year, such as black-grass.

Black-grass

Approximately 80% of black-grass germination occurs from August to October, according to Teagasc, and its seed sets from May to August.

This means spring planting reduces black-grass incidence significantly. The seed also needs light to germinate so ploughing plays a big part in the control of the weed.

Image source: Teagasc

Sterile brome

Approximately 90% of sterile and great brome germinates from August to December. The plant flowers from May to July and seeds are shed in July and August. Later planting can reduce incidence of the weed. For example, if wheat can be planted in November.

Unlike black-grass, sterile and great brome do not need light to germinate, but seed emergence is reduced when seeds are buried more than 10cm, so again ploughing can significantly reduce the number of plants that germinate.