Target weeds early to capitalise on successful autumn drilling

“What a difference a year makes,” says Matt Siggs, technical manager South, Bayer Crop Science. “It has been an excellent autumn for establishment. Oilseed rape is wall-to-wall, and most cereals have established very well too. That is certainly the case in my region but speaking to colleagues, it’s similar across the country.”

Huge contrast

Even later drilled crops for this season are quite advanced; for example, at the Bayer trial site at Hinton Waldrist in Oxfordshire, wheat drilled on 14th October reached leaf two just 3.5 weeks after sowing.

“It’s a huge contrast to last year, when many crops had to be drilled late and never really caught up, especially with the spring drought,” Matt adds.

He points out that weed control was quite good last season due to the enforced late drilling. This time around crops were drilled earlier, and consequently weeds also benefitted from the good establishment conditions. There is still some work to do to stop weeds putting a dampener on yields.

“This year we have crops with higher potential but a theoretically higher weed burden if we don’t act now and into the early spring. Even a low density of some weed species can cause significant yield losses and that is vital because good yields are going to be so important to restore cashflow on farms.

“The positive is that most farmers applied their pre-emergence herbicide and any top-ups as planned. Proclus (aclonifen) worked well alongside Liberator (flufenacet + diflufenican) and other mix partners at pre-em.”

Seedbed quality

According to Matt, seedbed quality was generally good which supported pre-em performance and in most cases, there was enough rain to provide the all-important soil moisture for efficacy. 

“I am a little concerned about some of the September drilled wheat because it stayed dry for 2–3 weeks after drilling which may reduce the control from the pre-em. Plus, we know that September drilling increases grassweed levels in the crop as it matches the germination curves of black-grass and Italian ryegrass particularly well. 

“The top up application has helped as a holding pattern but in these crops, I would be looking at using a post-emergence spray as soon as possible.”

If there is a suitable weather window you can apply Atlantis OD (mesosulfuron + iodosulfuron) relatively soon to target weeds while they are small and with less energy reserves to use in non-target site resistance mechanisms which metabolise the herbicide.

Mild winters are becoming very common, particularly in Southern England, so there could be an opportunity to apply during December or January. However, in most cases, agronomists will recommend waiting until February to start applying the post-em as product choices becomes wider.

“From 1st February, Atlantis Star (mesosulfuron + iodosulfuron + thiencarbazone) is the strongest option available for grassweed control. Weeds should still be small at this time and not going into stem extension which is primarily when we see issues with poor efficacy.

“Look for active growth in the weeds and ideally apply on a bright sunny day which helps optimise efficacy. As ever be careful of crops under stress from waterlogging or recent frosts that can dewax the crop and cause excessive bleaching.”

Monitor performance

In later drilled crops, monitor performance of the residual programme and any late weed germination before deciding on next steps. If there are grassweeds that germinated and were missed by the residuals, aim to apply a post-em as soon as the weather allows. 

Depending on the broadleaf weed species mix, consider Pacifica Plus (mesosulfuron + iodosulfuron + amidosulfuron) which has a good spectrum of broadleaf weed activity thanks to the amidosulfuron. The thiencarbazone in Atlantis Star also has good activity against some broadleaf weeds so check the weed spectrum carefully to choose the best product. 

Matt emphasises that the cost of spring weed control should be paid back in terms of protecting yield which is going to be crucial this season. The authoritative AHDB Project Report No. 560 established that 100 heads of black-grass equated to reduction of 1.08 tonnes of yield.

A well-timed post-em application will control some plants entirely, while for others it will suppress tillering and reduce headcounts, diminishing resource competition in the crop – all helping to protect yield. Added to that, fewer seeds go back to the seedbank, easing weed control for future seasons.

“Looking at how the autumn has gone; I expect disease management and crop nutrition are going
need careful management this year. Tick the weed control programme job off your list as early as possible so you can focus on other priorities.”

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