24 May 2002

Weed threat to maize

SOME maize crops face greater competition from weeds this summer, with growers dropping pre-emergence atrazine applications due to dry conditions at drilling.

Atrazine requires moisture to be effective, says MGA agronomist Simon Draper. "But dry weather at drilling meant atrazine was not applied, leading to a greater reliance on post-emergent weed control."

Weed control is crucial until maize plants reach the 10-leaf stage. For most growers, nightshade is the main problem, requiring one or more applications of a contact herbicide.

"There is a choice of herbicides, including Jester, bromoxynil, Shield and Titus, but bromoxynil is often the cheaper option. But care is needed when applying bromoxynil, as it can lead to leaf scorch." Spraying during a dull day or in evenings will minimise this risk, advises Mr Draper.

"An alternative strategy to avoid scorch is using a lower application rate instead of the recommended 2.5 litres/ha. This should be applied earlier at the 2-3 leaf stage, instead of the 5-6 leaf stage to ensure weeds are effectively controlled, although repeat applications may be needed."

Growers who spray early could also cut costs with the lower dose rates. But they need to act soon with some crops already at the two-leaf stage, he adds. &#42