6 September 1996

Plan your drilling to put blackgrass under pressure

STRATEGIC drilling can help beat resistant blackgrass. So says ADASs Jim Orson, chairman of the Weed Resistance Action Group*.

"Farming is all about taking opportunities, and the weather this year has given us a chance to get rid of a lot of blackgrass in problem fields through managing drilling dates. The hot, dry weather during seed maturation has shortened dormancy, so blackgrass will be able to germinate earlier in the current moist conditions."

Blackgrass always has some post-harvest dormancy, explains Mr Orson. "Subject to moisture availability, the autumn emergence will often be in significant numbers from late August onwards until around the middle of November, with a peak in September. That means that the earlier a crop is sown in this period, the more blackgrass will emerge after the crop is drilled and the more reliance there will be on selective herbicides for its control."

IACR-Rothamsted researcher and secretary of WRAG, Stephen Moss, has estimated from trials that for every days drilling during the main period in the autumn there will be a cut of about 2% in blackgrass numbers in the subsequent crop. "This year the advantage of delaying drilling may be significantly higher," says Mr Orson.

Lowering reliance on herbicides is part of the WRAG and Herbicide Resistance Action Committees** strategy to reduce or avoid the development of resistance, and sowing date has a significant role to play. "Drilling date of individual fields should include a consideration of avoiding herbicide resistance in blackgrass or slowing its development.

"While it is unrealistic to ignore the other agronomic requirements of drilling date, it would be wise to sow last those fields which already have or are at most risk from herbicide resistance in blackgrass.

"It is important to ensure that emerged blackgrass plants are killed prior to drilling and a non-selective herbicide should be used where there is a chance that they may survive seed-bed cultivations. Black-grass which is not killed before drilling will be very competitive, be most difficult to kill with selective herbicides and set large amounts of seed the following summer."

*WRAG is a UK body with input from researchers, ADAS, agrochemical firms and the PSD.

**HRAC is an international organisation of agchem firms. &#42

WRAG advice on blackgrass control this autumn:

&#8226 Hot, dry weather shortened weed dormancy.

&#8226 Current moist conditions are ideal for germination.

&#8226 Aim to cut herbicide dependency.

&#8226 Consider delayed drilling on fields most at risk.

&#8226 Ensure blackgrass plants are killed before sowing.


Later sowing, within reason, eases the battle against blackgrass, says WRAG.