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Crop Advice & Expertise

5 actions to consider when controlling black-grass in spring 2019

Depending when you drilled your wheat crops, weed control – especially black-grass – in spring 2019 might be looking like either a huge challenge or a case of finishing off the good work. Here are 5 actions to consider about your weed control strategy this spring:

1. Check pre-emergence control and establishment in winter cereals

Walk crops and check the level of control from autumn applied pre-emergence herbicides such as Liberator (flufenacet + diflufenican) as well as crop establishment. The general pattern this season is that later-drilled crops (second half of October) have much lower levels of black-grass while, earlier-drilled crops are seeing far more problems. Assess each field and categorise based on the success or otherwise of weed control in the autumn. 

2. Consider spraying off and re-drilling in the worst areas

Sometimes it is better to admit defeat and look at the long-term benefits than soldiering on and making the situation worse. If black-grass control in the autumn has been so poor that post-emergence herbicides and / or rogueing are unlikely to give good enough control levels and mean a high seed return, then it can be prudent to consider spraying off fields with Roundup (glyphosate) and re-drilling with a competitive spring crop.

Despite the extra work of re-drilling, the benefit should be much lower levels of black-grass at the end of the season and crucially in following seasons because seed returns will be much lower. 

3. Re-drill with competitive spring crops & minimise soil movement

A crop with a thick canopy that establishes and grows quickly is the best way to compete with black-grass in spring crops. Crop selection, seed rate and drilling date all affect this. The go to crop for most growers is spring barley, which is competitive with black-grass and potentially can attract malting barley premiums.

Only drill cereals when soil temperatures are warming up and suitable for good establishment and growth. Higher seed rates, even over 400/m2, can also help but farm knowledge about variety and soil type is needed to make sure lodging and other problems do not arise.

Try to establish spring crops with minimal soil disturbance after spraying off to minimise new black-grass germination. 

4. Apply post-emergence herbicides to winter wheat as soon as conditions allow

Where autumn control has been good, or lower populations of black-grass are present, then look for opportunities to spray as soon as conditions allow. Contact-acting herbicides like Monolith (mesosulfuron + propoxycarbazone) are more effective against smaller weeds – ideally at the 1–3 leaf stage. In early February, days are still quite short and cool, so the spraying window is only likely to be a few hours in the middle of the day. Prioritise fields that will get the most benefit from a post-emergence spray. 

5. Look for active growth 

Active growth is essential for a successful post-emergence herbicide application. The active substance is taken up by the weed more when the plant is growing than when in a dormant winter state. Sunshine and temperature both stimulate active growth. Even at cooler temperatures if the weather is sunny spraying can be effective – so get out into the field and assess whether active growth has started.