Getting the timing right for grassland herbicide application is vital, says Dow AgroSciences in the second of a series on weed control.
Now is the ideal time to be planning grassland herbicide application so weeds can be treated at the optimum time as soon as growth kicks into gear. The cold spring may have delayed weed growth this year, but experts are warning as soon as conditions improve, weeds could rapidly reach the ideal stage for treatment. In fact, the recent sunny spell seen across much of the country could mean farmers will need to go sooner rather than later.
Dow AgroScience’s grassland agronomy expert Andy Bailey explains: “As soon as temperatures rise, weeds will really motor away and farmers need to be prepared as they will reach the optimum stage for application very quickly.”
By applying herbicides early in the season, at a time when weeds are healthy and actively growing, farmers are likely to achieve the best levels of control and see the biggest long-term benefit to grassland performance.
Duncan Connabeer, technical support manager for Hutchinsons, says weed control is vital so as to maintain the quality of grazing swards and silage.
“A 10 per cent infestation of weeds results in a 10 per cent loss in grass yield. Docks also have 65 per cent of the feed value of grass, so are poorer quality and will lower forage intakes. If you are growing good quality grass, why would you put something in it with a poor feed value?” he asks.
As the cheapest form of feed available, Mr Connabeer believes all livestock producers should be looking to get more from grazed grass. “With the current milk price, dairy farmers in particular need to challenge how they can get more from forage produced on farm. That could be through reseeding with newer varieties and removing weeds to maximise performance,” says Mr Connabeer.
Generally perennial weeds such as docks, thistles and nettles are of most concern in grassland, as well as buttercups, dandelions and ragwort. Producers will see the biggest benefits from applying herbicides early, rather than having a ‘knee jerk’ reaction once weeds are established. As a result, planning ahead and applying the relevant herbicide when weeds like docks and thistles are at rosette stage and about 20cm tall or wide, is crucial.
Mr Bailey suggests farmers should plan herbicide strategy by looking at two areas. “Think back to last year and ask yourself where the weedy fields were, then walk the fields and look for signs of weed growth,” he says.
Weed infestation levels can be assessed by counting the population of docks or thistles in a 7m (23ft) by 5m (16ft 4in) area in each field. A count of 10 equates to a population of 10 per cent. When weed levels are under 5 per cent, then a spot spay could be used. At more than 5 per cent, broadcast treatment will be more cost-effective.
Mr Bailey says the next step is to choose the correct herbicide to treat the weed challenge. “If you only have a dock problem, select a narrow-spectrum herbicide. If you have a mix of docks, thistles and nettles then choose a wide-spectrum product.”
Established perennial weeds like docks and thistles should be controlled with herbicides containing either triclopyr or aminopyralid. Only products built around these actives are powerful enough to get into the extensive roots system and give lasting long-term control.
Weed challenges and treatment considerations will also vary depending on whether grassland is used for silage or grazing. Docks tend to favour fertile soils and as a result are generally a bigger problem in silage fields, while creeping thistle can be problem on grazing ground. In general, grazing fields will commonly have a broader spectrum of weeds than silage crops.
When treating weeds on silage ground, Mr Bailey says it is important to leave at least 21 days between application and cutting to ensure maximum efficacy of treatment. As a result, planning well ahead is vital.
Mr Connabeer says spring frosts mean some farms may have to re-evaluate how they treat silage to give optimum control of weeds.
“The frosty spells may have knocked weeds back so they are not actively growing. This can be seen by a red tinge on the leaves. If this is the case it may be worth delaying spraying or doing a split dose treatment,” he says.
A split dose treatment will involve the application of a half rate of long-acting spray now to achieve a clean first cut and then a second application on the regrowth after cutting.
However, Mr Bailey says when spraying with a long-acting, translocated product at the optimum time prior to cutting, it should not be necessary to apply herbicide again between cuts. “If for some reason you did miss the opportunity to spray, then it is possible to spray between cuts, but you need to provide sufficient time for the weeds to regrow, at least for 21 days after application.
Where grass is grazed, farmers should also do all they can to prevent weeds from establishing by ensuring effective grazing management. “Start with good grazing management early in the season so you maintain a dense sward. If you over- or under-graze you can create problems. For example, over-grazing will create bare soil and the ideal situation for weed germination. Topping weeds may also make you feel good, but it is not a good strategy for controlling weeds,” says Mr Bailey.
However, Mr Connabeer says topping can form part of Integrated Pest Management (IPM) for the control of creeping thistles. “Leys can be grazed tightly, topped in June and then sprayed. The topping results in uniform emergence of thistles so you get better control,” he explains. “This is a delay from the usual May treatment of creeping thistles so it won’t suit all systems.”
Where ragwort is a problem in grazing, early treatment is best as you want to spray before the plants go into their flowering stage. Ragwort can be a concern as consumption by livestock can lead to liver damage, reduced performance and even death. It is of particular concern after wilting as the plant becomes more palatable.
As a result, farmers must ensure they are completely decayed before letting stock back into pasture after treatment. Aminopyralid can also be used to treat ragwort in grazing situations and will give a good level of control, but farmers must talk to a BASIS qualified adviser before they use it.