Dow Shield: apply now to control key competitive high biomass weeds in forage maize

When Dow Shield (clopyralid) was first registered in the UK in 1976, over 40 years ago, maize was an insignificant crop grown on just 10,000 ha’s of land in the UK and AD plants on farms were relatively unknown. With the development of better maize varieties to suit our climate and the need for additional break crops, the area of maize in the UK has been creeping up – in 2012 it was 183,000 ha’s, in 2015 187,000 ha’s and in 2016 184,000 ha’s according to Defra’s agricultural census. A further rise is being anticipated this year when it may hit 200,000 ha’s. The Three-Crop Rule has led to more interest in maize and farmers want to spread their workloads or add energy production on farm. Another important reason is to introduce another break crop in order to get rid of difficult to control weeds such as black-grass and thistles. The majority of maize is forage maize, but there is a significant area of maize grown for energy production in AD plants. In past years around 20% of the total maize planted was grown for AD plants.

Peter Waite of Dow AgroSciences,says: “Yield is the overriding objective for maize. With the increasing area, there will inevitably be new growers of maize who will need advice on how to achieve high yields. Establishment of the crop is important as is placing the seed at optimum depth and spacing. Maize is a weak competitor during its establishment phase and its seedlings can easily be overwhelmed by weed competition, especially by high biomass weeds which colonise bare open soil between wide rows and take advantage of these spaces and the upright growth habit of the maize crop. Early removal of weeds such as thistles, sow thistles and mayweeds is essential to achieve good yields. With the first 6 to 8 weeks being critical to the crop’s development, any competition must be removed early. Crops are usually sprayed a number of times with herbicides, pre-emergence and early post-emergence, to ensure the crop grows through this vulnerable early stage.”

Dow Shield 400 was granted a full label recommendation for forage maize five years ago and is a very useful product to control high biomass, highly competitive weeds such as
sow-thistle, mayweeds, groundsel and corn marigold.

It is applied post-emergence to all varieties of forage maize at 0.25 l/ha from the 3 leaf stage up to the 9 true leaves of the crop. It shows very good crop safety, according to Peter.

“Maize forms the base feedstock for most on-farm AD plants, with yield being the key driver. Growers should be aware that when Dow Shield 400 is used in maize destined for the anaerobic digester, it takes 6 months for the chemical to breakdown and so the digestate should not be spread onto susceptible crops. Growers and advisors should be familiar with the Dow Shield label with respect to succeeding crops or ring the Dow AgroSciences Hotline.”

Be aware, Peter says, that most other herbicides, pre-emergence and post-emergence in maize have following crops restrictions. “Growers, especially those new to the crop, need to make sure they read all the labels thoroughly, so they are familiar with any such restrictions.”

Peter observes that maize drilling and emergence has been later this year in many areas due to the very dry conditions. Recent rains and warmer temperatures will create weed flushes just as the maize is establishing. Removal of weeds such as thistles, sow thistles and mayweeds will be even more important to achieve good yields.

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About The Author

John Swire - Deputy editor of Agronomist and Arable Farmer as well as responsibility for the Agronomist and Arable Farmer and Farm Business websites. After 17 years milking cows on the family farm John started writing about agriculture in 1998 and has since written for a variety of publications and has developed a wide circle of contacts within the industry. When not working John is a season ticket holder at Stoke City and also of late has become a fitness freak, listing cycling, swimming and walking as his exercises of choice.