Early drillers need to beware of blackgrass

17 August 2001

Early drillers need to beware of blackgrass

BE careful with stale seed-bed techniques when trying to deal with blackgrass, especially if min-tilling. Mistimed cultivations could leave a heavier weed burden for in-crop herbicides.

Pre-drilling cultivation to encourage flushes of otherwise dormant blackgrass before glyphosate spraying can help ease pressure on in-cereal graminicides, says Arable Research Centres technical co-ordinator Richard Overthrow.

"Its generally accepted that you can kill four times as much blackgrass out of crops rather than in them."

But Syngenta-sponsored ARC trials suggest that may not always be the outcome. Early drillers in particular need to beware of doing secondary cultivations too close to sowing. "It doesnt allow time for the second flush to become big enough for spraying off before drilling," says Mr Overthrow.

"If you are going down this route you have to give it time to develop a big enough spray target. Its much easier to kill blackgrass with glyphosate when its tillering than when it has only a single leaf, and may be shaded by trash, larger plants or volunteers."

The trial was on a site with known triple R metabolic resistance, says Syngenta technical manager Iain Hamilton. Nevertheless the work showed total control was possible. "The important thing is not to rely on a single input."

Bad weather thwarted plans to sow wheat, but it was decided to continue with the planned treatments. Avadex (tri-allate) was not applied until December and Hawk (clodinafop-propargyl + trifluralin) and Lexus DF (flupyrsulfuron-methyl) went on in late March. But the lack of crop competition makes the results even more meaningful, Mr Hamilton believes. "Control should have been easier if wed had a crop."

Depending on pre-sowing tactics and subsequent herbicide programmes, blackgrass kill ranged from zero to 100% (see table).

Cultivating late, especially for a second time, produced much higher weed burdens for the graminicides to deal with.

Rolling proved surprisingly effective at encouraging weed germination, probably pressing seed into the soil in damp conditions.

In most cases using Avadex pre-Hawk proved useful. &#42


&#8226 Stale seed-beds useful.

&#8226 Avoid late cultivation.

&#8226 Glyphosate needs good target.

&#8226 100% control still possible.

ARC/Syngenta cultivations/herbicide trial

Secondry Unsprayed Blackgrass % control

cultivation* (heads/sq m) Hawk Hawk + Avadex Avadex Lexus followed f/b Hawk by Hawk + Lexus

None 38 71 100 68 100

S tine (19 Sep) 112 50 98 63 100

S tine (5 Oct) 218 0 96 33 96

S tine x2 (19 Sep/5 Oct) 276 57 98 65 99

Roll (5 Oct) 56 64 98 82 100

* All treatments disced & pressed Sept 7. Glyphosate used after each pass as close as possible to expected drilling date. Head counts and control levels assessed June 26. All selective herbicides at full doses plus oil where required.

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