This autumn is already shaping up to be a much different autumn to 2022 with ground already much moister than last year. Farmers struggled to get good stale seedbeds last season because it was too dry for grass-weeds to germinate before drilling took place, says Bayer's Darren Adkins.
"In the circumstances, pre-ems did a good job but the conditions over the rest of the season tended to encourage weeds."
Given current conditions, the first priority is to create a really effective stale seedbed ahead of drilling. The moisture will also lend a hand to soil mobile actives such as flufenacet, so the only sticking point is how late farmers are prepared to drill.
"Late drilling is always a tricky topic, purely looking at weed control the answer is always drill later in the second or third week of October. If ‘late' means it is a spring crop because of the weather, so be it. In the real world, everyone wants to have plenty of wheat in the ground so it is about finding a balance and being prepared for the consequences of any decision. Plan to apply herbicides at the true pre-em timing, ideally within 48 hours of drilling."
Weed spectrum
Knowing the weed spectrum in each field is also important, efficacy of delayed drilling varies by species. It is very effective against black-grass and good against ryegrass, sterile and soft brome, but it is not suitable for other brome species.
"Where there are later germinating weeds, having good residual protection is important, even more so in early drilled crops. The best combinations tend to pair a product offering high initial control with a longer half-life active. Liberator (flufenacet + diflufenican) + Proclus (aclonifen) follows this pattern."
In high pressure black-grass and ryegrass situations, adding prosulfocarb to that programme gives extra impetus to initial weed control, he says. Further actives can be added but look to sequence rather than stack as it increases duration of protection and can help reduce crop effects which can be a problem on lighter soils.
"For autumn applications, there are actives from six different Herbicide Resistance Action Committee mode of action groups available, seven if you include an autumn contact post-em. Different modes of action use different chemical pathways to control weeds, attacking it in different ways improving control and preventing resistance," says Mr Adkins.
Mode of action
Results from Bayer's Mode of Action Survey 2023 (see graph below) showed that most farmers use three-four modes of action for wheat weed control with flufenacet, pendimethalin and diflufenican the most commonly used actives. With newer chemistry such as aclonifen and cinmethylin available there is more scope to rotate actives and have diverse weed control each season.
Source: Bayer Crop Science
"Regarding modes of action, the main question mark is about Group 15 which has flufenacet, prosulfocarb, tri-allate and ethofumesate, all of which are important pre-em actives. For example, tri-allate is good on wild oats and some brome species so you might want to pair it with flufenacet products. And as I mentioned before prosulfocarb and flufenacet work well in tandem against black-grass."
Where you are doubling up on Group 15s, the current guidance is that it is safe to do with sensible precautions such as only using two Group 15s in one programme and include other modes of action too.
"We also have more tools to target weeds this season. Aclonifen has been approved in barley at 1 litres/hectare since last season. On heavier soils, drilled correctly at the true pre-em timing it is an effective and safe option, but lighter soils are more of a danger. As ever attention to detail is key. There is also more scope to use metribuzin this season due label changes which is good alternative mode of action for weed control."
