Tailor spraying tactics to grassweed pressure
Tailor spraying tactics to grassweed pressure
In a normal year, blackgrass
starts to compete with the
crop in February. But the
unusual conditions
experienced this season,
together with the lack of
spraying opportunities, mean
bad blackgrass infestations
will already be causing yield
loss. We provide some
timely advice for control
GOOD blackgrass control will be difficult to achieve this year, so growers must prioritise their spraying workload according to weed size and density to do the best they can.
"The two things to bear in mind about blackgrass are that it is very competitive – just 100 plants/sq m causes a yield loss of 1t/ha – and that it germinates over a longer time after a wet harvest," says Dr Bob Bulmer, technical manager with Dalgety Arable.
"So keep looking – it may still come this season."
Resistance to herbicides is also on the increase, with more target-site resistance showing up in the last twelve months. In the field, it causes a very rapid breakdown in control of the "fop" and "dim" herbicides.
In recent years, theres been a move away from IPU to flupyrsulfuron (Lexus) as the cornerstone of control programmes, Dr Bulmer points out. This is often partnered with products such as clodinafop+trifluralin (Hawk) or pendimethalin (Stomp), depending on the other weeds present. So where Hawk has been chosen, there has been selection pressure.
Where earlier treatments have been made, they should be checked.
"Its been a good year for leaching, so if IPU was used go and see whats happening in the field. And the pre-emergence treatments, such as Avadex, will have no further contribution to make now."
Dr Bulmer has identified three different blackgrass situations this year, each one requiring a different course of action.
1 Big, well-tillered blackgrass
Fields which were drilled in September or October have big, well-tillered blackgrass plants already. These are the most urgent, as well as the most challenging.
Suggested Action: Use a Hawk/Lexus mix at full rates, with an adjuvant. Dont apply with lo-drift nozzles as a medium/fine spray is needed and choose an esterified rape oil adjuvant, such as Toil or Biosyl. Use 100 litres/ha of water to concentrate the adjuvant and get better uptake and coverage.
2 Small blackgrass
Later drilled fields, which have small, susceptible blackgrass populations. With these, there is a better choice of control options and a bit more time.
Suggested Action: For high populations, use a Lexus/Stomp mix. Otherwise, use IPU partnered with DFF or pendimethalin, or an IPU/chlorotoluron combination, such as Tolugan Extra. Opt for Hawk with difficult seedbeds, where blackgrass is germinating from depth. Exceeding 1500g of IPU at this time of the year contravenes IPU Stewardship.
3 Low blackgrass populations
Fields which have been drilled recently, or are very wet, where the weeds are not growing. Deciding to leave these fields is risky, especially if crops are thin.
Suggested Action: An IPU mix, such as Javelin Gold, ensuring that some residual has been applied.
Other situations
Growers who resorted to broadcasting their cereal crops must be careful if planning to use IPU, warns Dr Bulmer. "Spray from three leaves, once the roots are out of the way. Most products are safe to use after the three leaf stage."
Hawk is a good choice for these crops. "But remember, any crops that are still waterlogged should not be sprayed at all."
For crops just drilled play a waiting game and see what weeds emerge. Dr Bulmer believes these crops wont have much grass weed in them and adds that more cost-effective products may be appropriate.
Other weeds
Ryegrass and brome are the two other grass weeds which need controlling as soon as possible.
For ryegrass, Dr Bulmer recommends chlorotoluron followed by tralkoxydim (Grasp) while brome needs an IPU-based product, but at a higher rate than is allowed after the end of November. "If the brome has tillered, growers now have the new Monsanto product, Monitor."
Wild oats will come through until early May. Products used for blackgrass control, such as Hawk, will have an effect on any early wild oats.
Grass weeds in barley crops
The main active ingredients for use on barley crops are tralkoxydim, IPU, chlorotoluron and diclofop-methyl+fenoxaprop (Tigress Ultra). Dr Bulmers preferred mix for blackgrass is Tigress Ultra+IPU, with IPU being a good option for low weed densities.
Spraying conditions
Growers must strike the right balance between making the most effective treatment and using any opportunity to spray, acknowledges Dr Bulmer. He favours getting the sprayer out and reducing the pressure on workloads, but advises farmers to hold off if it is extremely cold.
"Ideally, you want active growth of the weed to get best results. But ground firmed by frost does allow the sprayer to travel."
Keeping adjuvant rates up will help and growers should opt for MSOs (esterified rape oils), which are less harsh on the crop.
"Dont forget BYDV control if the sprayer is going," stresses Dr Bulmer. "Crops which emerged before the middle of November are at risk. So add an aphicide to the tank-mix." *
Chemical costs
Chemical Rate Typical farm
cost (£/ha)
IPU 3 litres/ha 8.70
IPU/DFF 1+2 litres/ha 19.57
Lexus/Stomp 20g+2 litres/ha 29.50
Lexus/Hawk 20g+ 2.5 litres/ha 41.50
After the wettest autumn on record grass weed control has become a major headache for growers.Key to success is matching herbicide to individual field situations, says Dalgety technical manager
Bob Bulmer.
Latest application timings
Active Ingredient Apply Before
Tralkoxydim e.g Grasp GS39
IPU/IPU mixes e.g Javelin Gold, Panther GS32
Diclofop-methyl
+fenoxaprop eg Tigress Ultra GS32
Flupyrsulforon e.g Lexus GS31
Clodinafop+trifluralin e.g Hawk GS30
Pendimethalin e.g Stomp GS30
Chlorotoluron mixes eg Tolugan Xtra GS29