ENSURING BEST WEED CONTROL IN MAIZE CROPS
Ensuring a good maize crop depends on careful weed control. In the
run-up to drilling
Jonathan Riley outlines whats required
CHOOSING a spray programme for maize depends on the number of previous maize crops grown on the site.
Thats the view of Maize Growers Association agronomist Simon Draper who says that atrazine – applied at a maximum of 3 litres/ha in any one season – should still form the basis of control as it is cheap and effective particularly on sites where first crop maize is to 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 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," he says. "Weather conditions 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 seed-bed 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 chance 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, then a second application post emergence.
"In many cases the first application will be enough but watch for weeds because a further 1 litres/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 he recommends 3 litresha of atrazine is 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 up to a maximum of 2.5 litres/ha in any one season, he says.
"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 starane can be applied post emergence when maize ancillary roots are no more than 4cm long. To protect crops against thistles two applications of Shield can be made the first at two to four leaf stage," he advises.
To minimise 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. *
Atrazine should still form the basis of weed control – it is cheap and effective.
• Spray mornings or evenings to avoid hot dry conditions which cause scorch.
• Residual herbicides work better in moist conditions.
• Use a fine spray for contact herbicides to maximise coverage.
• Leave a 6m (20ft) buffer strip between sprayer and water courses.