23-06-2014 01:45 AM | Arable

Black-grass testing



With black-grass now flowering above wheat crops, it is easy to see where this weed has got the upper hand this season. In the next couple of weeks black-grass will start to shed seed and if growers don’t know the resistance status of their fields, it is well worth sampling black-grass seed to get it tested.

“We are in testing times as weed resistance is getting worse and weed control is becoming more challenging. You need to know what you are dealing with,” says BASF Campaign Manager Sarah Mountford-Smith.

“If you know the resistance status of your fields, it is much easier to come up with an appropriate programme to suit your needs. That may mean spraying off weed patches with glyphosate or spraying off the whole crop to prevent seed return. Or it may be that you need a robust autumn herbicide programme consisting of a number of actives including glyphosate, tri-allate, flufenacet, pendimethalin and DFF.”

“Whatever the solution, you need to know what you are dealing with. Knowing the exact nature of resistance will help support decisions on how to control black-grass using the most appropriate herbicides. Or it could be an early warning sign to a potentially more difficult problem down the line,” warns Sarah.

She also points out testing for black-grass must be carried out correctly and at the right time. “You need to collect black-grass seed when it is ripe. It is ready for sampling when the seeds are brown and fall off the panicle on their own, when you gently brush them with your hand. Don’t force the seeds off the plant and avoid intact seed heads. Sampling normally takes place the 2nd or 3rd week of July and when 10-20% of weed seeds have already shed, but this year seed is likely to be ripe late June.”

There are a few more hints and tips to get this testing right, says Sarah. “Avoid collecting black-grass seed from the edge of the field, but collect a representative sample from across the field, preferably across 2 or 3 tramlines and across an area of 100m. If there are patches of black-grass in the field, sample from each patch and mix the seeds together. Collect a small mug of seed and transfer it into a paper envelope, allowing it to dry for a few days. The seeds will then be ready to send to ADAS for testing.”

Ideally fields should be tested every three years to coincide with a typical 3 year rotation. Understanding the resistance profile of the black-grass population in the field will optimise control measures.

Sarah Mountford –Smith says that a lot of different factors went against us this year when it came to black-grass. “It was an autumn with low weed seed dormancy. In fact we saw the highest levels of black-grass seed germination for 6 years following the hot dry summer of 2013. We were also having to deal with a huge seedbank following two years of high dormancy. On top of that we had a mild winter and increasing resistance challenges. Of the resistance tests we offered farmers last year, 46% of the total samples exhibited resistance to all three mechanisms (enhanced metabolism, ALS target site resistance and ACCase target site resistance). This was up from 41% the year before.”

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