Managing three dreaded pre-harvest grass weeds

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Black-grass, brome and increasingly, ryegrass are problematic in many crops, with fully integrated solutions fundamental for effective control. Frontier agronomist, Harry Pitcher, provides his top tips for managing grass weeds pre-harvest as part of a long-term eradication plan.

“Residual herbicides appear to have worked well this season when field conditions allowed the full programme to be applied. However, where this hasn’t been the case, there’s the potential for higher seed return,” says Harry.

To reduce population pressure and prevent longer-term grass weed issues, Harry notes that limiting seed return is key.

“There needs to be a structured plan to identify the true state of grass weed numbers. A programmed approach for the remainder of the season and beyond can then be implemented.”

Growers can map the current issue in Frontier’s leading digital platform: “Mapping areas of concern can be done via the iSOYLscout tool in Frontier’s farm management platform, MyFarm. This helps form a clear picture of where the issues are and, more importantly, helps determine why there’s an increase in grass weed populations in that area in the first place.

How growers come to know the resistance status

“Resistance can occur both in the form of target site resistance (TSR) and non-target site resistance (NTSR). Knowing the current herbicide-resistance status helps inform future management decisions and the most appropriate herbicide strategy.

“When sampling seed for black-grass resistance testing, for example, make sure the seed is ripe. In general, the best time to sample is the second or third week in July, when 10-20% of seed has shed,” Harry advises farmers.

Handling the pre-harvest

“Review the grass weed pressure and if it’s in small areas, hand rogueing may be the most feasible and economic solution. Patch spraying the worst affected areas is effective but if the pressure is too high, consider spraying the entire field. It’s not ideal but will benefit future crops.

“Novel harvest weed seed control options such as chaff tramline should also be considered ahead of harvest.”

Post-harvest stubble management

Harry recommends post-harvest stubble management to reduce the population for next season.

“This is dependent on the specific grass weed issue. For example, with black-grass, if there’s adequate soil moisture for germination, cultivate and create a stale seedbed as soon as possible after harvest. If bromes are the problem, ploughing is most effective at helping to manage, compared to ryegrasses where a stale seedbed approach is worth employ

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