New guide to aid all-out assault on blackgrass

A new guide aims to give practical guidance to help control blackgrass mre effectively. Andrew Blake reports.

Timeliness, whether in making the most of stale seed-bed opportunities or spraying pre-emergence herbicide treatments, must be high on the list of growers’ priorities this autumn, BASF‘s Phil Brown says.

He readily acknowledges growers’ heavy autumn workloads. “But drilling is only half the story,” he says. “Pre-ems really should be used pre-em, for example. Spraying a little bit late can cause big problems.”

Two separate surveys, of growers* and agronomists**, which lie behind a new guide to best practice in managing blackgrass, Good2Go, produced jointly by BASF and Monsanto, suggest timeliness is not high in growers’ thinking.

Indeed it hardly figured in the grower survey, despite nearly all growers expecting autumn weed control to become more challenging.

“It’s not something that’s much on farmers’ minds,” says Monsanto’s Sue Mintern.

Stale seed-beds, as here on former FW Barometer farmer Ben Atkinson’s land,
need preparing carefully to make the most of the weed control opportunities they provide

BASF’s Will Reyer says interviews with agronomists, three-quarters of whom said blackgrass was their main grassweed problem, confirmed that.

“They said the importance of timeliness is not highly enough recognised.”

Cleavers, as expected, remains their main broad-leaved weed concern, though cranesbill and groundsel were also highlighted.

Increasingly aware that the blackgrass threat needs managing proactively, the agronomists said they would be making a real effort to apply treatments pre- rather than peri-emergence.

Only in some northern counties did they consider other grassweeds more troublesome.

Losing IPU and trifluralin would clearly affect weed control costs, the survey suggested.

“Most agronomists reckoned they’d see an increase of 10-30% in costs,” says Mr Reyer. “But getting farmers to accept that doesn’t seem to be a problem.”

Spray with glyphosate as soon as their is sufficient weed growth, the Monsanto/BASF Good2Go advice says

Persuading them to invest in effective herbicide programmes was rated an insignificant challenge by nearly two-thirds of those surveyed.

The loss of trifluralin would be felt much more in the east, where it has been widely used in mixtures, than the north and west, he notes. “It will be missed.”

As well as concentrating more on earlier pre-emergence applications the agronomists surveyed believed rates would have to be increased to compensate for the lack of alternatives.

Chlorotoluron would inevitably be more widely used as a substitute for IPU, though it had “shortcomings”, notably in that it should not be applied to certain varieties, noted Mr Brown.

Among agronomists flufenacet-based herbicides – for example, Crystal and Liberator – were clearly their main choices, accounting for 90% of their likely selections. But Mr Reyer acknowledges that prosulfocarb (as in Defy) may have been “under-represented” in the survey.

But the really telling point was increasing recognition of the role of cultural controls.

That was also highlighted in the growers’ survey, says Miss Mintern. “They clearly identify weed control outside the growing crop, whether pre-harvest, pre-planting or pre-emergence as the key to meeting the increasing challenge they face.”

Despite the workload and energy constraints, nearly a quarter were expecting to plough more to achieve better weed seed burial to try to keep on top of the problem.

Stale seed-beds in many cases merit better preparation, suggests Robert Plaice. “Discing a stubble and leaving it rough doesn’t create a stale seed-bed.” To ensure maximum weed seed germination, especially at a time of year when the weather is often dry, the soil must be consolidated, probably by rolling, he says. “It’s all about doing the job right.”

To help growers determine which management methods are most appropriate for their particular challenges, the BASF/Monsanto team have drawn up the Good2Go table. Along with explanatory notes it offers solutions for all three types of blackgrass, from relatively “easy” to “hard to control”, says Mr Brown.

Good2Go advice

Stale seed-beds and Roundup (glyphosate)

• Four weeks between harvest and drilling should give time to control annual grassweeds with two pre-drilling glyphosate sprays
• Leave stubble short and chop straw consistently to about 10cm (4in). Spread straw and chaff evenly over the whole combine width.
• Cultivate and consolidate the top few inches of soil as soon as possible after harvesting to provide an ideal environment for weed seed germination, even in dry summers.
• Good consolidation ensures high level of soil contact essential for rapid germination of small weed seeds, as well as preserving moisture.
• Inspect stale seed-beds closely and at regular intervals – even if fields look brown from a distance.
• Spray with Roundup as soon as there is sufficient weed growth – usually within 14 days.
• Cultivate and consolidate the ground again as soon as product label allows to stimulate a further flush of weeds for treatment ahead of final seed-bed preparation and drilling.
• Two stale seed-bed cycles always give better control than one by overcoming the problem of early weed seedlings inhibiting germination of other seeds.

Plough/non-plough

• Most grassweed, including blackgrass, germinate within the top 5cm (2in) of soil.
• Ploughing can reduce blackgrass populations by 25-80% and tine cultivating to 10-20cm (4-8in) by 20-40%.
• When ploughing ensure adequate burial of seed and trash to prevent germination of blackgrass.
• Before ploughing consider what seed seeds may be brought back to the surface from previous seasons. Blackgrass seed can remain viable in the soul for three years.
• Consolidate the soil’s surface after cultivations to preserve moisture.
• Non-ploughing favours grassweeds – make use of stale seed-beds.

Drilling date

• Later drilling allows more blackgrass to germinate and be controlled with two to three glyphosate applications.

Pre-emergence treatments

• Essential part of resistance management strategy for blackgrass and other difficult to control grassweeds.
• Pre-ems remove blackgrass early before it competes with crops.
• Fine, firm tilth will improve performance.
• Good seed-beds, with largest clods <3cm (<1.2in), help maintain minimum 32mm (1.25in) drilling depth for adequate seed cover and crop safety.
• Good application technique, with fine/medium droplet spectrum, will improve soil coverage and increase performance of shoot uptake herbicides (eg pendimethalin).

Post-emergence treatments

• It is important to preserve the activity of high resistance risk post-emergence active ingredients by:

1. Maximising the use of cultural techniques
2. Using pre-emergence herbicides to reduce the pressure of later applications
3. Saving high resistance risk post-emergence herbicides for more severe blackgrass populations
4. Not relying on high risk post-emergence sprays as the sole means of control

• Monsanto survey last March of about 300 growers in 50 counties of England, Wales & Scotland covering nearly 80,000ha (200,000 acres).

Read the Monsanto survey results.

** BASF survey last June of 43 agronomists (roughly half independent, the rest from distributors) covering an estimated 6% of the English and Welsh winter wheat area. Visit www.agricentre.basf.co.uk, and click on “autumn weed control adviser survey” just below log in box on right-hand side menu.