26 May 1995

Maize crop weeds need to be tackled right now

By Michael Gaisford

WEEDS that are developing fast in forage maize crops drilled a month ago need tackling now.

Due to the recent dry conditions, pre-emergence Atrazine has not worked well this year, and weeds are strongly competing with maize crops now at the four- to five-leaf stage, reports Simon Draper, consultant agronomist to the Maize Growers Association.

"Weeds need to be controlled as quickly as possible before they affect the growth rate of young maize plants," says Mr Draper.

"Choice of herbicides to use will depend on which weeds are the major problem and whether or not Atrazine was used as a pre-emergence herbicide this year and in previous years," he says.

Due to higher than acceptable levels found in watercourses in recent years, the standard herbicide for weed control in maize, Atrazine, can now only be used at a maximum rate of 3 litres/ha in any one growing season.

If 2 litres/ha has already been used in a pre-emergence weed control application, the remaining 1 litre/ha allowed is best used post-emergence with a partner chemical, advises Mr Draper.

He says that the partner chemical of choice will depend on the particular weed problem on the farm, and that the use of a mineral oil with the Atrazine will improve its contact efficiency considerably.

If Atrazine has not been used pre-emergence, Mr Draper says that used with oil at the maximum 3 litres/ha, the product should give good weed control in fields where it has not been used in previous years, and resistance to it has not been built-up by weeds like black nightshade.

To be considered

In these circumstances, forage maize herbicides like Lentagran, Bromoxynil, Stomp, Starane and Shield should be considered.

Where the weed problem is mainly black nightshade, Mr Draper favours an Atrazine/ Bromoxynil cocktail, and where fat hen is the dominant weed he reckons a mixture of Lentagran and Atrazine will do a better job.

He also warns of a risk of leaf scorch of young maize plants this year due to the need to spray the crop earlier than usual where pre-emergence Atrazine has failed.

To give an additional and immediate boost to young maize crops, whether or not they are having to compete with weeds, and as a supplement to root-fed fertilisers, some growers are now using foliar sprays.

One of the alternatives is the Maxicrop seaweed extract, which has new recommendations for use this year. "Little and often" applications of 1.5 litres/ha are advised. Cost is £4.50/ha (£2/acre).

Weeds need to be controlled as quickly as possible before they affect the growth rate of young maize plants. Atrazine has not worked well in dry.