While the vast majority of maize crops are now too tall to consider post emergence applications it is worth making a few points for next season:

• Canopy cover was slow to develop this season.
• Post-emergence sprays have little residual activity. The frequent drizzly showers while doing  little for the maize crops have encouraged further flushes of weeds.
• Timing is absolutely critical, larger weeds are harder to kill. It is better to spray too early than too late. Attempt to spray grass weeds before they tiller.
• Always use sprayers set up for inter-row spraying to avoid wasting spray on maize foliage.
• Our trials have shown mesotrione formulations applied before grass weeds tiller (generally 2-3 weeks post-emergence) followed by nicosulfuron formulations 2-3 weeks later, gave very good control of grass weeds.
• Newer herbicides such as topromezone (Arietta) give good control of grass weeds, especially when mixed with atrazine and a suitable adjuvant.
• Always read the label and follow it and be wary of adjuvant use with a mixture that includes dicamba.
• Do not repeatedly apply the same chemical year after year without alternating to another mode of action.

Those who have applied herbicides according to all of the above and still suspect there is a problem are invited to contact either Mike Parker (021 960 078) or Trevor James (021 0458 305), as resistance may be the problem.

Source: Mike Parker (FAR) and Dr Trevor James (Agresearch)