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Black-grass control

First identified in 1982, herbicide resistance in black-grass is widespread throughout the main arable regions of England. Avadex is a key tool in both the prevention and management of black-grass populations.

Herbicide resistance is the inherited ability of a black-grass plant to survive a herbicide that would normally give effective control. There are two main types of resistance. These two mechanisms are independent and each can occur alone or in combination with the other. The commonest form of resistance is enhanced metabolism.

Plants with enhanced metabolism detoxify herbicides and have cross-resistance to many different herbicides. The resistance is often partial rather than absolute. The cross-resistance can be to several herbicides with the same, or different, modes of action.

The other form of resistance is target site resistance where the site of herbicide activity within the black-grass is blocked. This resistance is absolute. This form of resistance is less common but it is increasing.

Avadex Excel 15G belongs to herbicide group N as classified by the Herbicide Resistance Action Committee (HRAC) – a different mode of action to many other commonly used grass-weed herbicides.


Prevention and management of resistance

Strains of some annual grasses (e.g. black-grass, wild-oats and Italian rye-grass) have developed resistance to herbicides which may lead to poor control. A strategy for managing and preventing such resistance should be developed. Guidelines have been produced by the Weed Resistance Action Group and copies are available from the HGCA, CPA, your distributor, crop advisor or product manufacturer.

Avadex Excel 15G should only be used for control of herbicide resistant strains of annual grasses as part of an appropriate management strategy, including cultural control methods and sequences with herbicides of alternative modes of action.

Key aspects of the Avadex Excel 15G resistance management strategy are:
• Always follow WRAG guidelines for preventing and managing herbicide resistant grass weeds.
• Maximise the use of cultural control measures wherever possible (e.g. crop protection, ploughing, stale seedbeds, delayed drilling, etc.).
• Use a programme of tank mixes or sequences of herbicides with different modes of action within individual crops, or successive crops.
• Where products are approved for both pre- and post-weed emergence applications, apply pre-emergence where possible when resistance is suspected.
• Apply post-emergence products/mixtures to small, actively growing weeds, especially where high levels of resistance are suspected and to reduce the risk of resistance development.
• Monitor weed control effectiveness and investigate any odd patches of poor grass weed control. If unexplained, contact your agronomist who may consider a resistance test appropriate.


Use cultural control measures. Don’t rely only on chemical control

• Cultivation strategy – for example rotational ploughing.
• Crop rotation – spring cropping as well as winter; broad-leaved crops as well as cereals. Consider fallowing.
• Delay drilling and use a stale seedbed to control black-grass seedlings. Spray off emerged black-grass with glyphosate.
• Crop competition: higher seed rates of a competitive variety may help smother the black-grass.
• Prevent seed return and spread around the farm from combines and other farm machinery.


Acknowledgements:

The resistant management guidance provided here is based on the “Revised Guidelines for Preventing and Managing Herbicide-resistant grass weeds”, produced by the Weed Resistance Action Group (WRAG) and published by HGCA, from which copies are available free of charge.