28 April 1995

Keeping your maize weed-free

OVER the next few days and weeks, a record UK area of forage maize will germinate and emerge. So too will a host of weeds.

Choosing the right control programme will depend on the fields recent cropping history and the weed control used immediately before drilling.

Most growers have probably applied about 2.0 litres/ha of atrazine (Atrazine) before drilling, which will have killed most common weeds. The notable exceptions are nightshade and a further dozen moderately resistant weeds like buttercup, dandelion and knotgrass. If the ground has been used for maize in previous years, weeds like fat hen may have become resistant to atrazine.

"After drilling, and before the maize crop comes through, the field should be checked for signs of couch or other grass weeds," says Simon Draper, consultant agronomist to the Maize Growers Association.

"If there is much sign of grass weeds, they should quickly be sprayed with Roundup before the maize comes through," he advises.

Where atrazine was not applied before drilling, Mr Draper says there is no reason why it too should not be applied before the maize crop emerges.

As the crop emerges a careful check should be made for signs of pest damage, and for any weeds emerging with the maize. "Where weeds do germinate with the maize, the first job is to identify the species, assess its possible effects on the maize crop, and then take the appropriate remedial action," advises Mr Draper.

This will usually involve spraying weeds at the 2-4 leaf stage. Mechanical weed control is only advisable where a skilled and experienced operator is available, recommends Mr Draper.

Apart from atrazine, the other main herbicides to consider either with atrazine or as an alternative are pyridate (Lentagran), bromoxynil (in mixes) and pendimethalin (Stomp). Mr Draper reminds all growers that new Ministry regulations restrict the use of Atrazine to about 3.0 kg/ha depending on which commercial product is used this year.n

If herbicides are not applied to forage maize as necessary, there will be more weeds than maize at harvest time,as shown in this untreated plot in one of Simon Drapers field trials.

Inset: A weed-free crop at this stage of growth should be the aim of every grower. Product choice is critical.