Still time for residuals in blackgrass fight

Growers who have been unable to get any pre- or peri-emergence herbicides on to wheat crops because of the wet weather are being urged by agronomists to get some sort of residual on in the next two to three weeks.

Speaking at a Dow press briefing, cereal herbicide specialist Stuart Jackson highlighted that growers are limited on how much flufenacet they can use.

“It goes down to 120g/ha for applications made after the end of December, but you’ve got the opportunity to bolster with PDM, chlorotoluron [CTU] or some prosulfocarb.”

According to Mr Jackson, this year has brought three scenarios. Those who are either getting their pre- or peri-emergences on are in good shape and can follow these up in the usual way with Unite (pyroxsulam + flupyrsulfuron) plus an adjuvant with or without an additional residual when there is active growth of the target weeds.

“Those who haven’t got anything on so far should really focus on getting some sort of residual on as soon as they possibly can and although we are limited on how much flufenacet we can use, there are options.

“There is the opportunity that if we’ve got active growth at the same time then they can apply a tank mix of Unite plus a residual herbicide, such as 120g/ha flufenacet or 1.75 litres/ha Stomp Aqua (pendimethalin), or Auxiliary (clodinafop + prosulfocarb) up to growth stage 24 of the blackgrass can be applied.

The use of additional residual with Unite should be considered when applications are made during January and February, especially where blackgrass is small and there is a concern with subsequent emergence.

If growers are unable to get active growing conditions in January, these recommendations still apply in February in terms of tank mixing with the residual.

However, if growers still haven’t been able to get an opportunity by the end of February, then Mr Jackson advises an application of Unite on its own, with the efficacy of a residual reducing significantly.

“CTU is an exception in terms of tank mixing. It’s a sequence only this time of year, where you are targeting blackgrass. You are looking at a minimum four-week – ideally six-week – interval between an application of CTU and any product containing pyroxsulam,” added Mr Jackson.

One thing that has worked in the farmers’ favour, according to NIAB TAG’s weed biology specialist John Cussans, is that delayed drilling has had a positive effect on blackgrass populations, protracting its emergence and lowering numbers.

The latest Grassweed Emergence Monitor confirms this, suggesting all grassweed will be small coming into the spring.

“This offers an opportunity for grassweed control with pyroxsulam-based products, such as Unite or Broadway Sunrise (pendimethalin and pyroxsulam), when there is onset of active growth. In the absence of blackgrass, Broadway Star is a more cost-effective option for many grassweeds.

“The benefit of additional broad-leaved weed control is an additional advantage from all three pyroxsulam products,” says Mr Jackson.

Independent agronomist Sean Sparling believes if growers are able to get on the land, then a tank mix of 0.3 litres/ha of Liberator (diflufencian + flufenacet) with Atlantis (iodosulfuron + mesosulfuron) or another residual is a possibility, providing there has been a previous application of 0.6 litres/ha in the autumn.

Defy (prosulfocarb) offers another alternative for a tank mix with Atlantis that has worked well in previous years.

Although there is an opportunity to get residual products on, Mr Sparling warns that the amount of sodden fields with water still stood in them mean farmers should not rush into forcing anything on.

“There is an increased risk of uptake of the residuals from the plant in these conditions because of the amount of water around, so growers should be extra cautious.

“Getting the conditions correct will also be key, as in many cases it may be the only chance you get to hit the blackgrass. If you’re applying Atlantis, wait for active growth with the soil temperature 6C for at least five days before and then at a dry leaf for at least four hours after.”

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