DO NOT leave blackgrass populations unchecked until the spring, cereal growers have been advised.

Where blackgrass populations are high (200+ plants per square metre), growers need to select a herbicide with good strength and persistency, said Velcourt’s Keith Norman.

In such situations, and where you are considering applying Atlantis (mesosulfuron-methyl + iodosulfuron-methyl-sodium) post-Christmas, he recommends a robust pre-emergence product like Crystal (flufenacet + pendimethalin).

But in low or medium (50-200 plants per square metre) blackgrass situations, cheaper Uranus (linuron + trifluralin) or Uranus/Stomp (pendimethalin) or Liberator (flufenacet + diflufenican) mixes can be more appropriate, he said.

“Uranus is not a stand alone, one hit product, it is best used with partners as part of a fully integrated pre and post-emergence package. If you tank mix with Stomp or Liberator you are gaining a wider spectrum of control and increasing blackgrass efficacy as well.”

Atlantis can take a lot of pressure off pre-ems, providing they are applied at the optimum timing, but growers must ensure they do not let a lot of blackgrass come through to the spring, he said.

“The length of time the weeds have been left unchecked in the autumn and spring is important in terms of final yield.

“A lot of trials only focus on percentage weed control, but if this doesn’t take place until March, for example, blackgrass could already have had a significant impact on yield.”

Blackgrass germination will not be protracted this year, as dormancy is very low following hot, dry conditions during maturation, Mr Norman added. “There’s a lot of blackgrass coming through as we speak, so Uranus combinations should work well in low or medium blackgrass situations.”

Another alternative for those looking to use Atlantis in the spring is to introduce isoproturon as a different autumn holding component in the spray programme, he suggested.

The more active ingredients used, the lower the risk of further resistance build-up, he said.

See this week’s FARMERS WEEKLY magazine (23 September 2005) to find out where three popular pre-emergence blackgrass herbicides should be positioned and what pitfalls to look out for.