Blackgrass control is increasingly moving below ground, as attention turns to building crop
root systems that can compete more effectively with the weed.
Growers have made significant progress against blackgrass over the past decade. Average
counts at Hutchinsons’ Cambourne grassweed site in Cambridgeshire now stand at 60
plants/m2, compared with 600 plants/m2 at the former Brampton site 10 years ago. But
even relatively small populations can still have a major impact, warns Hutchinsons technical
manager Dick Neale.
“The problem is that these surviving blackgrass plants tiller their socks off, so we could still
end up with a lot of heads and a lot of seed return,” he says. Left uncontrolled, a population
of 50 plants/m2 could return 150,000 seeds/m2.
Work at Cambourne has highlighted three practical levers that can help growers keep
blackgrass populations in check.
1. Use placement fertiliser to support establishment
Placement fertiliser — particularly phosphate — can provide valuable insurance during crop
establishment.
In Hutchinsons trials with PrimeStart, the benefits included stronger establishment, better
tiller retention and changes to crop architecture.
“We don’t need a lot of P, but we need it available to the crop roots,” says Mr Neale. “We
are using phosphate rather than nitrogen to drive plant growth in the early part of the
season, creating a much more robust plant that can compete with weeds much more
strongly.”
2. Build competition with variety blends
Although end-market requirements may limit their use in some situations, variety blends in
feed wheat and barley offer a way to increase crop competition against blackgrass.
At Cambourne in 2026, trials compared KWS Dawsum with a farm blend of SY Insitor,
Gleam, Champion and Dawsum. The PrimeStart-treated blend reduced the average
blackgrass head count by 60% compared with the single variety.
“Blends provide more competition than single varieties,” says Mr Neale. “We are learning
that competition needs to come from the root system. We’ve got to compete with the root
system of blackgrass and generate as much root growth in the wheat crop as we can.”
3. Sequence herbicides to match emergence
Herbicides remain the main driver of control. At Cambourne, a full-rate sequenced
programme reduced blackgrass head counts almost 20-fold compared with a single active
used alone.
Timing is crucial. Hutchinsons monitoring indicates that blackgrass emergence is becoming
later and more protracted. It begins in the first week of October, but small numbers can
continue to emerge through to mid-November.
Rather than relying on one large pre-emergence stack, Mr Neale says a sequence of actives
offers the best chance of matching the extended emergence window. The aim is to maintain
an effective dose of herbicide in the soil as new plants appear.
“We’ve got to make sure we’ve got herbicide active in the soil from the first of October to
the middle of November,” he says.
Keep pressure on the seedbank
With overall populations lower but emergence more drawn out, the priority is to build a
competitive crop from the outset. That means placing phosphate where young roots can
reach it, using variety blends to strengthen crop competition and sequencing herbicides
around the weed’s emergence pattern. Together, these measures can reduce the
opportunity for survivors to replenish the seedbank.
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