14 March 1996

Good spray strategy helps

hit potential

An effective herbicide programme cuts competition in the maize crop, allowing plants to establish a good root structure and reach their yield potential. Jonathan Riley reports

MAIZE herbicide programmes should be based on the number of pre-vious maize crops grown on the site.

Maize Growers Association agronomist Simon Draper suggests that though atrazine can only be applied at a maximum of 3 litres/ ha in any one season, it should still form the basis of control because it is cheap and effective, particularly where first-crop maize will be grown.

But he warns that weed resistance – particularly in black nightshade, orache and fat-hen – can develop on sites where previous maize crops have been treated.

"For sites drilled following arable or grass, and where there is no known history of weed resistance the recommended maximum of 3 litres/ha should be applied pre-emergence. The weather should be considered because atrazine is a residual herbicide and is activated by moisture. When dry spells are forecast, atrazine should be incorporated in the seedbed so that it lies close to the weed seeds. In wet weather atrazine applied in this way would be washed further away from the weed seeds so surface application is advisable in wet weather," says Mr Draper.

He recommends that when there is a possibility of resistance, for example where maize is in its second successive year, applications of atrazine should be split with 2 litres/ha applied pre-emergence followed by a second application post-emergence.

"In many cases the first application will be enough but watch for weeds because a further 1 litre/ha of atrazine mixed with a contact herbicide bromoxynil may be necessary when maize is at the two- to four-leaf stage to hit weeds as they emerge," he says.

"Where weed resistance has developed, 3 litres/ha of atrazine should be mixed with 1 litre/ha of bromoxynil applied at the two- to four-leaf stage. When further weed flushes occur additional bromoxynil can be used but only to a maximum of 2.5 litres/ha in any one season.

"Pendamethalin could be used as an alternative to control fat-hen, orache and black nightshade, but it must be used in moist conditions. For these weeds and for cleavers fluroxypyr can be applied post-emergence when maize ancillary roots are no more than 4cm long. To protect crops against thistles two applications of clopyralid can be made, the first at the two- to four-leaf stage," he advises.

To reduce herbicide use Mr Draper suggests inter-row cultivations are extremely effective and can also promote seed germination by aerating the soil, which also allows the soil to warm up. &#42

Maize Growers Association agronomist Simon Draper says that reducing competition from weeds at establishment allows the crop to achieve its full yield potential. Atrazine, which is cheap and effective, should form the basis of control, he advises.

Before the spraying season begins, choose a herbicide mix that is tailored to suit the site where the maize is to be grown.


ATRAZINE TIPS


&#8226 Atrazine is only for use with maize or sweetcorn.

&#8226 Recommended dose of 3 litres/ha a year must not be exceeded.

&#8226 Spray from ground based sprayers should not fall within 6m of surface water or ditches.

&#8226 Wash containers thoroughly and dispose of washings as recommended.

&#8226 Heavy rain soon after application may cause run off on steep gradients.

Source: Novartis.


SPRAY ADVICE


&#8226 Avoid spraying in hot dry conditions to prevent scorch.

&#8226 Residual herbicides work better in moist conditions.

&#8226 Use a fine spray for contact herbicides to maximise coverage.

&#8226 Leave a 6m buffer strip between sprayer and water courses.