Arable News

  • Written by: Farmers Guide
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Target black-grass better

 
Black-grass is among the hardest of all weeds to hit with a contact herbicide, but there are things a sprayer operator can do to increase the likelihood of a good application.
 
After last autumn, few winter wheat crops are sitting in fine yet consolidated seedbeds – a problem which will effect more than soil-to-seed contact. When it comes to grass weed control, clods and uneven ground cause spray shadows, reduce boom stability and can affect the efficacy of all contact herbicides.

 

Black-grass is among the hardest of all weeds to hit with a contact herbicide, acknowledges former sprayer operator of the year, Steve Lake. Its long, thin shape gives it a low surface area and vertical growth means that even when droplets hit it, there is a risk that product will run off.

 

But there are things a sprayer operator can do to increase the likelihood of a good application. From the order which you fill the tank, to nozzle choice, boom height, forward speed and timing – you can make a big difference to a products efficacy, he says.

 

Mr Lake only sprays Atlantis WG (mesosulfuron + iodosulfuron) onto actively growing black-grass and when the leaves are dry. If there is a film of water covering the leaf, the product could run off before the plant has had time to absorb the active substance – you cant expect it to stick to water, he explains.

 

The composition of Atlantis WG also makes the order in which you fill the tank important.  Biopower is the best adjuvant for Atlantis WG and while adjuvants do many things, its role in enhancing Atlantis WGs rainfastness, or stickiness, is what is key. Half the water volume should go into the tank first, followed by Atlantis WG, then the biopower and finally, the remaining water.

 

To increase his chances of hitting the target, Mr Lake keeps his boom height as close to 50cm above the crop as he can. Just 20cm higher and drift doubles, he says.

 

He keeps forward speeds low too; not exceeding 12.5km/hr. This is even more important when youve a cloddy seedbed.  The higher the speed, the greater vortex and the greater the shadowing effect will be.

 

With his Bateman RB35, he favours Defy O3 jet nozzles, alternated forwards and back down the length of the 30m boom.  By alternating them, you get a double spray edge and are more likely to hit both sides of clods. With a flat fan youll have a curtain of spray moving forwards and the shadowing effect will be worse.

 

With a small target like black-grass you need a fine to medium spray.  Sometimes people make the mistake of thinking that a higher pressure will lead to a finer spray and a better application. In reality you are better to lower the boom height and increase the water volume – this way, youll increase the number of droplets hitting the target, but with the same amount of product.

 

Theres no doubt that the weather last autumn didnt help seedbed preparations, but by getting the application technique right you can optimise control, concludes Mr Lake.

 


  • Written by: Farmers Guide
  • Posted:
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