Settled weather is providing an opportunity to control problem weeds with contact-acting herbicides before they get out of hand. Darren Adkins of Bayer outlines five tips for late autumn sprays.
1 Check weed levels
Many October drilled crops went into wet or less than ideal seedbeds, leading to slow establishment and lower pre-em efficacy. Drilling was the priority, so the pre-em programme was often delayed or missed altogether in some cases.
Wet and cloddy seedbeds both affect pre-em performance so many crops have fairly high weed levels in need of control. Earlier-drilled wheat is also likely to have grass weed pressure despite good establishment and good conditions for the pre-em.
2 Control blackgrass
Small plants with 1-2 leaves are typically more susceptible to post-em sprays like Atlantis OD (mesosulfuron + iodosulfuron) and Hamlet (mesosulfuron + iodosulfuron + diflufenican).
At early growth stages, the dose of active can overcome metabolic resistance, whereas large plants in spring are more able to survive. Maximising blackgrass control will pay dividends by improving yields and reducing seed return for future seasons”
3 Protect against further germination
With the trend to milder winters, weeds can continue germinate even in December and January. Applying additional residual herbicides, mixed with the post-em or as a standalone top up will give crops added protection.
4 Effective application
Apply a fine–medium spray to a dry or drying leaf with plenty of drying time before dew formation. Active growth is important – be wary of applying when temperatures drop close to zero as weeds may become dormant and not take in the herbicide.
5 Check BYDV risk
Returning to the crop to apply a post-em may be an opportunity to use an aphicide to control aphid vectors of barley yellow dwarf virus if there is risk. Use the T-Sum calculator and walk crops to decide if you need to spray.