Weeds - Grass Weeds Information and Photo Gallery

Black grass

Weeds_blackgrass.jpg (5026 bytes)

Appearance

Black grass (Alopecurus myosuroides.) is also known as Black Twitch. It is an annual grass that can grow to a height of 80cm. The foliage is greenish purple. The sheath is smooth. Individual blades are pointed, 3 to 16cm long and 2 to 8 mm wide. Panicles are yellowish-green, spike-like and 2 to 12 cm long. It produces single, large flowers during the summer.

Occurrence and spread

It is a common weed on arable land with no preference for heavy or light soils. It is scattered throughout the British Isles and frequently found on cultivate land in the SE of England.

Cases of resistance have been noted throughout the UK. It is a difficult weed to eradicate but if resistance is suspected or is known in your area a resistance management strategy is essential. Seed is produced in very large numbers and these are shed before the crop is harvest. However, the seeds do have a short period of dormancy and viability.

Control and management

Blackgrass can be a serious problem. It can be reduced by surface cultivation and possibly eradicated by two years of fallow. There are a wide range of herbicides available which will give good control. If resistence is suspected ensure appropriate action is taken. Economic control threshold is 2 plants per square metre.

Field trails carried out by ADAS and others have shown that clodinafop-propargyl+trifluralin (Hawk) can provide good control.

There are good opportunities to control blackgrass if winter oilseed rape is included in the rotation. Metazachlor containing products give a reasonable level of control and can relieve reliance on fop/dim products - therefore helping with a resistance strategy.

Knowing the type of blackgrass present will help significantly in deciding which herbicide is likely to be most effective. Based upon field trials over several seasons it has been possible to devise a systematic approach to control.

Categorise the type of blackgrass present.

  • It is MODERATE if the area infected is less than half the crop area and its decreasing. This type of blackgrass is usually controlled with a single spray and hawk should be able to cope. Modify the application rate to the weed size and combine with IPU if broad-leaf weed control is also required.
  • It is BAD if the area infected is around 30% of the crop and it shifts. In this instance a more effective management regime may be required. Probably at the full recommended dosage. Partner with IPU for broad-leaf weed control.
  • It is RESISTANT if the area infected is 18% and increasing. Usually this type of blackgrass needs confirmation via

Resistence tests. Indicators of resistance include a record of poor and variable control and some weeds surviving next to some that have been killed. If Resistant blackgrass is confirmed then use tri-allate pre-emergence plus a post-emergent treatment which will depend upon the resistance type. Seek advice from your BASIS qualified adviser.

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