When Dow Shield (clopyralid) was first registered in the UK in 1976, over 40 years ago, maize was an insignificant crop in the UK and AD plants on farms were relatively unknown. With the development of maize varieties that suit our climate and the need for another break crop, maize has increased its area with close to 200,000 hectares anticipated this year. This growth may be for one of four reasons – as a consequence of the Three-Crop Rule or to spread the workload or to introduce another break crop on the farm in order to get rid of difficult to control weeds such as black-grass or to add to energy production. The majority of maize, according to the June Census 2015, is fodder maize, but there is an area of maize that is grown for energy production in AD plants. Last year 19% of the total maize planted was grown for this purpose – so nearly 1 in 5 fields are destined for the AD plant now and 4 in 5 are forage maize. (81%).
“When growing maize, yield is the overriding consideration. But maize is a weak plant during establishment and maize seedlings can be overwhelmed by weed competition, especially by those high biomass weeds that grow quickly. Weeds colonise bare open soil between the rows and take advantage of the wide rows and upright growth habit of the maize crop. Early removal of weeds such as thistles, sow thistles and mayweeds is essential to achieve yield. Crops are generally sprayed two or three times with a herbicide, pre and early post-emergence, to ensure the crop is able to grow through this vulnerable early stage,” says Peter Waite of Dow AgroSciences.
Dow Shield 400 was granted a full label recommendation for forage maize in 2012 and is a very useful product to control high biomass, highly competitive weeds such as sow-thistle, mayweeds, groundsel and corn marigold. It can be 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, despite its post-em window.
“Maize forms the base feedstock for most on-farm AD plants, with yield being the key driver. Growers, particularly new growers, need to 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. If the digestate is spread onto grass, cereals, oilseed rape or maize, there are no worries. It is better to be safe than sorry and follow the advice on the label or ring the Dow AgroSciences Hotline,” says Peter. Obviously the majority growing forage maize do not have to worry about this specifically but do have to follow the label.
The label text says ‘Dow Shield 400 residues in plant tissue (including digestate) which have not completely decayed may affect succeeding susceptible crops. If treated crop remains have not fully decayed by the time of planting following crops, avoid planting peas, beans, other legumes, carrots, potatoes, lettuce, glasshouse and protected crops. Winter beans and peas should not be planted in the same year as treatment. Where susceptible crops are to be planted the following spring, do not apply Dow Shield 400 later than the end of July of the previous season.’
Be aware, Peter says that other herbicides, both pre-emergence and post-emergence, used in maize have following crops restrictions. “Growers, especially those new to the crop, need to make sure they read the labels thoroughly, so they are familiar with any restrictions on following crops.”