Focus on details for vital weed control boost

“In early October, farms are at different points in their autumn fieldwork,” explains Emma.

“Some have already finished their cereal drilling and pre-em programmes, while others have most of their acreage still to do. In every situation there are ways to improve weed control this autumn.”

Application 

Delivering the herbicide to the target is just as important as choosing the best products for the job. Applying the first residual at the true pre-em timing within 48 hours of drilling should be a priority for anyone with drilling to do.

“We often see pre-ems applied much later because farmers focus on drilling. I understand why it happens, particularly in bad weather. But if weeds are a concern getting back relatively soon means you get the best possible control from the herbicides,” Emma says.

She points out that lowering water volumes much below 200-litres/ha to increase work rates can impact herbicide performance. Proclus (aclonifen), and other actives that control shoots as they emerge, forms a film across the soil surface. Lower water volumes make getting full coverage of the soil more of a challenge. 

Consistent spray application is important for all herbicide applications. Underdosing areas can give weeds an opportunity and overdosing could cause crop effects hence a boom height of 50cm and forward speed up to 12kph is recommended.

Follow-up applications

Applying herbicides in a sequence rather than a very large pre-em stack has a number of benefits. It can help with crop safety and ensure higher levels of residual protection throughout peak weed germination. Follow up timing and product choice depend on the situation in the field.

“On the whole, herbicides offer a very good return on investment, but no one likes to apply herbicides unnecessarily,” acknowledges Emma.

With a sequence you can assess crop quality and condition before investing more. If this is your thinking, you can’t skimp too much on the pre-em. Firstly, because it is usually the most effective timing. Secondly, because there is the risk you can’t get back for the second application. 

“A metribuzin co-form like Alternator Met, Cadou Met and Octavian Met (all metribuzin + flufenacet + diflufenican) with Proclus, is a solid foundation for the programme at pre-em.

“Drilling depth of at least 32mm ensures there is physical separation between seed and herbicides. If the crop is well drilled into a good seedbed you can apply at the most effective timing. But on light soils, around heavy rain or if drilling depth is variable, then prioritise safety.”

Make sure you use different chemistry for the follow up than the pre-em for resistance management and to boost weed control. Also factor in efficacy against any broadleaf weeds you may have which will otherwise need controlling in spring.

“Cranesbill, groundsel and burr chervil are all well controlled by a metribuzin co-form. If you haven’t used it at pre-em, then I would use it at the follow up if any of these weeds are a problem for you.”

Emma notes that follow up applications also happen around the same time as the first BYDV spray but often the timings don’t quite match. Ideally, apply both sprays at the optimum timing and be aware of the compromise if determined to make only one pass with the sprayer.

Long-lasting protection

“We are seeing autumn conditions continue until much later in the year, this means weeds can continue to germinate for weeks or even months after drilling.

This is particularly a problem with ryegrass and some species of brome which tend to emerge later. But where there is a large enough seedbank, you will find late germinating black-grass too.”

Step one to combat protracted germination is using long-lasting actives in the pre-em stack. Proclus provides good grassweed control and has a long half-life as well as being light stable. Diflufenican and pendimethalin are other key actives with a good half-life.

“Accurately predicting how long you get protection from a herbicide is difficult. Herbicides break down more quickly in warm, moist conditions.

“Soil type and biology also influence the speed of decay. If you are worried about protracted germination, four weeks is probably the longest I would leave it before applying a follow-up. In warmer weather, I would go sooner.”

Emma recommends including at least one active with a long half-life at every timing, that means whatever happens with the weather, there is some insurance against late germination.

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