Early harvest offers blackgrass control opportunities

Freshly shed blackgrass seed is expected to germinate more readily than in recent seasons, following the hot, dry conditions experienced during May and June as the seed matured.

John Cussans, weed science principal consultant at ADAS, says the conditions mean blackgrass seed is ready to germinate as soon as conditions become favourable.

John Cussans, ADAS (Image: BASF)

“In hot and dry conditions, blackgrass seed tends to develop with lower dormancy,” he says. “That means once moisture arrives after seed shed, we would expect a greater proportion of seed to germinate relatively quickly, which growers can then combat ahead of autumn drilling.”

However, if soils remain dry after seed shed, the seed simply will not chit, regardless of dormancy or cultivation strategy.

An exceptionally early harvest could allow growers to create up to three stale seedbeds before autumn drilling (Image: Seeded)

“As we move into autumn, growers need to tailor both cultivation and drilling decisions to the conditions in front of them. If it’s still dry and dusty, further delaying drilling may be necessary to wait for sufficient moisture and maximise stale seedbed opportunities.”

With harvest taking place so early, many growers will have several weeks – and in some cases a couple of months – before drilling begins, says Mat Hutchings, senior commercial technical manager for the East Midlands and Ireland at FMC.

“That gives much more opportunity to create one, two or even three stale seedbeds before autumn drilling, depending upon available moisture, helping to reduce blackgrass populations before the crop is established.”

Hot, dry conditions can produce blackgrass seed with lower dormancy, encouraging faster germination once moisture arrives (Image: Seeded)

Keep seed near surface

Lighter cultivations generally work best in a low-dormancy year because they keep blackgrass seed close to the soil surface, where it is more likely to germinate.

Mat explains: “In higher dormancy years, ploughing can sometimes help by burying seed that would otherwise emerge over an extended period. This year, from a blackgrass perspective, it’s generally a season to avoid ploughing and instead encourage as much seed as possible to germinate before drilling.”

Although dormancy conditions may be favourable for this year’s weed seed, Mat warns growers not to base their entire strategy on current dormancy levels.

“Low dormancy is all well and good for this year, but fields won’t just contain seed shed this summer. They will also hold blackgrass seed from previous seasons, potentially going back three or four years, and that seed may have a wide range of dormancy periods.”

Build robust pre-emergence programmes

Lower dormancy also has implications for herbicide strategy. With more blackgrass expected to emerge during the main autumn flush, a robust pre-emergence stack is likely to deliver the greatest benefit.

“In a lower dormancy season there’s often more value in investing heavily in the pre-em because a larger proportion of the population is emerging together,” says Mat. “In higher dormancy years, sequences become more important because emergence is spread over a much longer period.”

Recent trial work from FMC supports this approach.

“Data from the last two seasons has shown that using Fundatis first in the programme delivers around a 10% improvement in blackgrass control compared with programmes using the same chemistry but positioning Fundatis later.

“For blackgrass situations, Fundatis can be partnered with cinmethylin to achieve good levels of control in a mix or sequence. When targeting high-pressure sites, adding aclonifen, pendimethalin or Liberator (flufenacet + diflufenican)-type products can provide a very robust programme.”

Fundatis contains the actives bixlozone and beflubutamid, both of which are new to the market in Great Britain. It can be used pre-emergence and early post-emergence in winter wheat, and pre-emergence in winter barley, to control problematic grassweeds including blackgrass and ryegrass, and broadleaved weeds such as groundsel and speedwell.

Lighter cultivations can keep blackgrass seed near the surface, encouraging germination before the crop is drilled (Image: Seeded)

Know your weed populations

Many of the same management principles apply to Italian ryegrass, although understanding emergence patterns is particularly important.

“Some ryegrass populations emerge mainly in the autumn, while others have a protracted germination with a significant spring flush,” says Mat. “Knowing which type you’re dealing with is critical because autumn residuals will have great difficulty controlling populations germinating predominantly in the spring.”

The same applies to blackgrass populations, which can adapt over time in response to management.

“If you’ve been delaying drilling for several years, your blackgrass population may have shifted its peak emergence into late October,” he explains. “The most effective strategy is to understand the emergence pattern on your own farm and tailor drilling accordingly, by either establishing the crop ahead of peak emergence where appropriate, or delaying drilling until after the main flush has passed.”