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MAJOR WEED PROBLEMS LOOMING
Date added: 27/06/05 |
- Poor break crop management contributing to weed crisis
- Resistance at critical levels
- Return to traditional weed control and management essential
Poor break crop management, the increasing trend towards minimum tillage
methods and ever earlier drilling dates are now creating major grass weed problems throughout the UK, warns ProCam technical director Dr. David Ellerton.
Furthermore, reliance on late spraying rather than appropriate pre and post
emergence treatments is damaging yields and fuelling a significant resistance to the most effective herbicides.
The trend is doubly frightening because of the speed in which the problems are escalating and also because there is little left in the arsenal against the major grass weeds once resistance has really taken hold, he warns.
The stark warning was made at ProCam’s NIAB Open Days on Wed/Thurs 22/23 June, when David Ellerton said analysis of ProCam’s 4cast crop information from the last 5 years, suggested an urgent return to better basic weed control practices was now essential.
“All the major grass weeds are showing marked increases since 1999 with the
percentage of badly affected areas rising from 31% to 52% and significant resistance now seen in 29% of the country as opposed to 18% just 5 years ago.
The bottom line is that we need to achieve 97% control of Blackgrass in any year simply to stand still - any less than this and the seed burden will be worse than the previous year. Modern practices mean this level of control is simply no longer happening.
The 4 cast data clearly shows first wheats on many soil types now have an extra £3- 4/ha of herbicide spent on them over second wheats, showing break crops are no longer fulfilling their role as cleaning crops due to poor management.
The data also shows nearly 40% of Winter wheat now going into minimum tillage seedbeds compared with 18% five years ago and an extra £10/ha being spent on herbicides in crops drilled into these seedbeds compared with traditionally cultivated ones.
There are significant fixed cost savings with minimum tillage but with nearly 60% of blackgrass seeds germinating in the critical 0 – 2.5cm soil depth, it offers virtually no control of grass weeds due to its failure to bury seeds deep enough to inhibit germination.
The compounding issue is the earlier drill dates now being used. The earlier you go the more you are having to control weeds when the crop is germinating and the more you’re going to have to spend later.
“It’s no longer just a question of having to spend more because of these new
practices, the real issue is whether the herbicides work at all – and if so, for how much longer?” David Ellerton says.
“We are now reliant on just two main groups of chemicals -ACCase and ALS
inhibitors, including Fops, Dims and Sulfonylureas. Resistance to Fops and Dims is now so great that they are extremely unreliable particularly on large blackgrass plants.
Resistance to ‘Topic’ for example, has now been found in 47 out of 49
samples taken from throughout the UK in a recent survey.
That leaves the Sulfonylureas as the main means of late post emergence grass weed control, with ‘Atlantis’ the most popular. However, there is a worrying trend towards farmers applying ‘Atlantis’ inappropriately, leaving it until late in the spring before spraying large grass weeds.
“4cast shows last year 70% of crops had Atlantis applied in the period February to May, with many applications towards the end of that period. This means the crop has had at least six months competing with a highly aggressive weed so there will be a significant drop in yields.
Our data shows that in one trial the yield difference between autumn treated and spring treated crops was 11.2t/ha to 9.2t/ha – a drop of nearly 2t/ha, despite high levels of blackgrass control.
“More worryingly, spray late and you’ll knock out everything except the resistant strains and the seeds of these are what you are left with to deal with next year. If you really want to drive resistance across the country – spray late on big weeds!”
The Solution
The only way back from this situation is to think more about basic weed control and challenge agronomists who are advocating inappropriate advice without an understanding of these key issues.
“In winter wheat, we have got to be prepared to drill later on difficult grass weed fields, so we can get appropriate pre-drilling treatments on stale seed beds and avoid the main flush of germination occurring in the crop. Precede late post emergence treatment with either pre- or peri- emergence sprays and remember to apply insecticides in late October /early November even if no herbicides are being applied at this time.
Use minimum tillage wisely and in sympathy with the weed problems already existing. Make sure you are happy that the savings do stack up on your individual farm.
“Pre-drilling and early autumn treatment are essential in winter barley. You have to get on early as you don’t have options later on. For winter OSR and beans, make sure you manage them properly so they act as cleaning crops and utilise alternative modes of action such as propyzamide, carbetamide and simazine where appropriate.
“Finally, don’t rely on chemicals alone. You must adopt an Integrated Crop
Management approach taking into account drilling dates, rotations, cultivations and the environment. Anybody who is just recommending a purely chemical approach is not only a poor agronomist they are now being grossly irresponsible.” |
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