Conditions looking good for early sown OSR... and weeds


With soils generally moist and temperatures typically around 14-16oC, conditions are looking good for early sown OSR. However, inevitably this means conditions are also good for weed growth and we're already seeing flushes of black-grass emerging in young crops as seen in this emerging rape crop near Colchester earlier this week.

Timing is everything to gain control of these early grass weeds and they need a programmed approach; carbetamide (such as Crawler) and clethodim (such as Centurion Max) will provide early autumn control. Meanwhile, propyzamide (AstroKerb) is available to use later when soil temperatures drop and weed growth slows. 

The importance of water conditioner and timing

Black-grass seen in rape crop near Colchester, 8th September 2017

Young grass weeds can be small, difficult targets and poor quality herbicide applications will compromise performance and increase the risk of resistance developing further. Clethodim is contact-acting so maximising deposition and retention on leaves will pay dividends. Using medium/fine spray droplets, applying to dry target leaves and keeping sprayer booms stable will all increase successful herbicide uptake.

Time clethodim applications for when black-grass has reached at least the 3-leaf stage. This ensures each plant catches sufficient herbicide to take up a lethal dose. Leave an interval of at least 10 days after any previously sprayed treatments (including micronutrients and biostimulants) and, if you are in a hard water area, ensure water is adequately conditioned.

To ensure effective herbicide performance, growers in hard water areas will need to take extra care. This is because the performance of some plant protection products is impaired by mixing with hard water.

The 'dim' group of herbicides are particularly susceptible to reduced performance in hard water situations (e.g. clethodim as used in early autumn control programmes). Frontier trials have clearly demonstrated the improvement effective conditioning of hard spray water, using a product such as Aquascope, makes to the performance of clethodim applied to black-grass in OSR.

Water conditioner should be added to the tank first and mixed with the full volume of spray water before adding clethodim (Centurion Max) to the tank. 

OSR trial showing application of clethodim at 1.0l/ha rate without water conditioner (left) and with water conditioner (right)

In a season of mixed conditions, there is some OSR still to drill but for those that got in early, the weeds are already demanding careful attention.

​Paul Cartwright

Crop production specialist

For specific advice for your business related to this blog or any other aspect of crop production get in touch with Frontier.

Brand names used are Trade Marks of other manufacturers for which proprietary rights may exist. Use plant protection products safely. Always read the label and product information before use.

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