The role of Kerb in tackling weed resistance
UK - November 16, 2010
Dr David Ellerton, Technical Development Director of Hutchinsons, regards the problem of grass-weed resistance as a major problem for arable farmers and one that continues to escalate. "Last year was a particularly bad year for black-grass control and a lot of weed seed was shed where weed control was inadequate. As well as utilising cultural control methods to lower the weed seed burden, crops such as oilseed rape and beans have a crucial role to play in breaking the cycle and managing weed resistance."
David points out that oilseed rape and beans need to return to their crucial role as cleaning crops in the rotation. "This means that we need to pro-actively use different chemistry in broad-leaved crops than we do in cereals and to make sure that we get weed control spot-on in these crops. For this reason residuals such as propyzamide, carbetamide and, to a lesser extent, metazachlor all have a role to play."
"Propyzamide can give very good levels of control of black-grass and rye-grass, but conditions of application need to be right. Weed seeds need to germinate in the top few centimetres of the soil, so that their roots develop in contact with the residual herbicide. If weeds germinate from depth, results won't be as good. So keep tillage to a minimum."
Dow AgroSciences have been conducting a large field-scale trial in Poundon, near Aylesbury to evaluate the role of tillage, crop and herbicide in grass-weeds control. David Roberts, Broad leaved Crops Agronomist for Dow AgroSciences, explains that they are in year two of a three year trial to examine rotational opportunities for weed control in wheat with Broadway Star and Broadway Sunrise and in oilseed rape with Kerb Flo. "Overlaying this we are also looking at the impact of different establishment techniques on weed populations and control. Already there have been some positive conclusions. The first is that, even though ploughing reduces the number of black-grass plants, the results with Kerb Flo are much better on minimally tilled plots. This is because weed seeds that are retained in the top few cms of the soil germinate within the propyzamide treated layer of soil. Ploughing buries weed seeds where they germinate from depth."
"The second lesson we have learnt is that when it comes to black-grass, it is well worth sticking to the full label dose rate of 2.1 l/ha for Kerb Flo rather than 1.7 l/ha. Grass-weed control requires a longer term approach with the objective of reducing weed burden to the greatest degree at every stage in the rotation. When you have an opportunity to hit weeds hard, you should do so. Kerb Flo controls all black-grass, irrespective of the type of resistance carried," says David Roberts.
David Roberts advises the strategic use of different herbicide chemistry with varied modes of action. "Propyzamide should be included in any rotational weed resistance management programme. We are fortunate to have propyzamide which is from a distinct group of chemicals, the benzamides. It has no known resistance problems in respect of black-grass, rye-grass or wild-oats, all weeds that have increasingly common and widespread de-sensitisation to other groups of chemistry. And, providing you get conditions right for performance, it plays a vital role in tackling susceptible and resistant grass-weeds across the rotation."
When it comes to the right conditions, Dr. David Ellerton advises that propyzamide needs to be applied at the right time when weeds are small and not growing too fast. "If weeds are still growing, they can grow away from the chemical, resulting in poorer control. You also need sufficient soil moisture and cool soil temperatures - around 8°C and falling is ideal. If it is cold, the residual life is much longer and the end-effect much better. In most seasons, and indeed this season, these ideal conditions will be from mid November onwards. It's worth waiting, so that the best results can be achieved." For difficult black-grass populations, David advises adding a contact graminicide to add that extra reliability.
Dr. Ellerton adds that growers must choose a good quality propyzamide such as Kerb Flo from a reputable manufacturer such as Dow AgroSciences. "Then you'll know that you are getting a top quality formulation with the right amount of active ingredient that mixes easily and is applied easily with no hiccups. By choosing a propyzamide from Dow, you'll be supporting a Stewardship campaign to help minimise any of the product getting into water. It is imperative that growers adhere strictly to guidelines to avoid any risk of water pollution.
A strong Stewardship campaign not only advises how best to do this but also invests in further research to look for further positive advice. It also helps advisors by communicating such findings and seasonal factors to aid best results."
"As propyzamide has a different mode of action to all herbicides used in cereals, it is an important resistance management tool. There is no evidence of resistance to propyzamide, despite the many years of use, and if used when conditions are optimal it can make a real contribution to breaking the grass-weed cycle."
He adds a word of warning however "If propyzamide or any other residual is found in water above levels set under the Water Framework Directive, we are at serious risk of losing these valuable tools."