Leading the fight against Black-Grass

Even the most intractable and costly grass weed problems can be overcome with the right management, the necessary determination and sufficient time.

Understanding, commitment and flexibility are the main keys to success.

 

Focus on the worst-infested fields first

Not all your fields will require the same level of Black-grass management emphasis.

Coding each field red, orange or green in the summer on the basis of Black-grass risk enables the most rigorous controls to be concentrated on where they are most needed.

Equally, fields with the less pressing Black-grass control needs can be ear-marked for less intensive weed management attention for valuable savings in both hassle and cost.

Warning: An apparent absence of Black-grass in a single season should not automatically result in a green coding, though. Instead, the history of each field should be at least as important a consideration.

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Plough well to bury seed but not more often than every 4-5 years.

Rotational ploughing can give excellent immediate Black-grass control, especially if it follows years of shallow tillage, offering a valuable ‘reset button’ in red-coded fields.

Ploughing will not be as effective where Black-grass seed is spread throughout the soil profile and ploughing again within 4-5 years will bring viable seeds back to the surface to germinate.

Several years of shallow tillage is recommended after ploughing to keep any remaining Black-grass seed near the surface where it can be controlled with glyphosate stale seedbeds.

Direct drilling can also be employed between rotational ploughing to keep Black-grass seed near the surface and wake up the least amount of it through soil movement.

Warning: To be most effective ploughing needs to give complete soil inversion and bury all trash. Otherwise, too much Black-grass seed will escape burial at a depth from which it cannot emerge.

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Delay autumn drilling or introduce spring crops

As a rule, red or orange-coded fields should not to drilled with wheat before mid-October to enable early germinating Black-grass seedlings to be eliminated with pre-planting glyphosate.

Choosing wheat varieties for this slot on the basis of their known Black-grass competitiveness and using higher seed rates is also advisable.

Where September drilling is important for workloads, wheat can be replaced with substantially more competitive six-row barley providing the Black-grass risk is not too high.

Spring cropping or fallowing is recommended for red-coded fields to allow the greatest amount of Black-grass growth to be stimulated and sprayed-off before the next crop is planted.

Warning: Without active measures to control Black-grass, spring cropping and fallowing are unlikely to be effective in managing the problem. In many cases a single spring crop or fallow may not be sufficient where there are high levels of weed seed in the soil profile.

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Prioritise Black-grass control in every cereal break crop

Regardless of field coding, full advantage should be taken of every opportunity break crops provide to control Black-grass in the rotation.

Unless preceded by winter barley, pre-planting glyphosate control opportunities are limited in winter OSR, but combinations of clethodim, carbetamide and propzamide offer effective in-crop control.

Later sowing gives much more time for pre-planting control ahead of winter beans which also offer good in crop control opportunities with carbetamide and propyzamide.

Spring crops offer the greatest pre-planting control opportunities, either in stubbles or through the use of cover crops effectively sprayed off ahead of drilling.

Warning: Less-than-ideal Black-grass control has become common-place in modern cereal breaks, putting unnecessary extra pressure on management in the inherently more challenging cereal parts of the rotation.

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Move as little soil as possible at drilling

Whenever crops are drilled in red and orange-coded fields, as little soil as possible should be moved at drilling to ‘wake-up’ the least amount of Black-grass.

Applying as much to spring as autumn drilling, and to break and cover crops as much as cereals, this will make a useful contribution to reducing the viable seed bank in the soil.

Separate seedbed preparation in advance of drilling needs to be avoided, as do drills which actively cultivate more than the immediate drilling strip as part of their operation.

Direct and strip till drills tend to move less soil than other cultivator drill types but this may not always be the case.

Warning: Standard tines on many cultivator drills can still move too much soil. Using narrow points has been found to substantially reduce Black-grass emergence in the seedbed.

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Integrate cultural controls with the best herbicide programmes

Although Black-grass can no longer be reliably controlled with herbicides alone, cultural controls should always be integrated with the most appropriate spraying programmes.

Glyphosate is vital to remove all Black-grass growth before drilling, and where planting is delayed by more than a few days a permitted glyphosate is also recommended post planting but pre-emergence of the crop.

Robust residual pre-emergence and peri-emergence cereal herbicides are essential in red and orange-coded fields, with sufficient moisture and fine, firm seedbeds vital to success.

Where cereal crops still have high levels of Black-grass in the spring spraying-off patches  – or even whole fields – with glyphosate will be important to limit seed return.

Warning: The effectiveness of all but a few selective cereal herbicides depends upon the resistance status of the Black-grass population. Resistance testing is always advisable to ensure the most cost-effective chemical use.

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Identifying Black-grass

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Seedling

  • Leaves are fine and smooth with shiny upper surface, often blue-green; stem bases are often purple.
  • Leaf blade is twisted with a blunt tip.

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Heads

  • Compact narrow pointed panicle 2-13cm long and 3-6mm diameter.
  • Often tinted purplish
  • Produce on average 100 seeds per head

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Characteristics

  • Tall erect annual grass 20-90cm tall forming either a single shoot or clump depending on the competitiveness of the crop; stems round and slender with few nodes.