Delaying wheat drilling on bad blackgrass ground for little more than a month can improve margins and reduce future weed problems dramatically, according to the latest results from one major blackgrass trial site.

In addition, if conditions don’t favour late winter wheat sowing, the work shows that a spring alternative offers substantial performance improvements.

Pictured: Late drilled wheat (above left) shows an advantage over that drilled early (right) in bad blackgrass fields.

See also: Get timing right for blackgrass destruction 

In the studies on heavy land with some of the country’s most challenging blackgrass populations on the distributor Agrii’s site at Stow Longa near Huntingdon, the winter wheat variety Solstice, sown on 1 November, yielded an average 7.76t/ha in 2013 over a range of cultivation systems to generate a £903/ha margin.

In contrast, the same variety sown at the same seed rate across the same range of cultivation systems on 27 September averaged just 4.82t/ha with a margin of £389/ha.

What’s more, delaying drilling for about four weeks cut blackgrass levels from more than 200 ears/sq m to less than 20 ears/sq m, and so reduced the weed seed return to the soil.

Agrii’s national agronomy manager Colin Lloyd told more than 150 growers visiting the site at a late June open day that drilling later had improved control of blackgrass.

“All our detailed establishment system research over the past four years shows highly significant improvements in yield and reductions in blackgrass from delaying drilling,” he said.

Mr Lloyd added that this takes a huge amount of pressure off post-emergence herbicides, which is welcomed news as the best blackgrass control the trials have shown with the post-emergent product Atlantis on the site is now down to just 25%.

“Regardless of whether you plough, min-till or direct drill, sowing after the middle of October is essential if you are to combat bad blackgrass,” he said.

Mr Lloyd added that growers need to give enough time for weed seedlings to emerge so they can hit them with glyphosate ahead of sowing.

“In our experience weed seed dormancy levels have little effect. Unless the ground stays bone dry right through to drilling you’ll get a good flush of blackgrass. And the more flushes you can stimulate and spray off ahead of sowing the better,” he said.

Mr Lloyd admits delaying drilling is a risk as if conditions turn against growers on the sort of ground where blackgrass is prevalent it may mean growers can’t get a decent crop of winter wheat.

“Drill too early, though, and – like many growers this past season – you could be faced with the expense of having to write-off large areas of badly infested crop. The choice is yours,” he said.

His work shows that leaving the worst blackgrass ground for later drilling needn’t be nearly as risky it may seem. Indeed, parallel trials with six varieties of spring wheats sown on 4 April last year in the next-door field with equally high blackgrass levels delivered an average yield of 6.46 t/ha with a £729/ha margin and a zero weed population.

While not rivalling the performance of the later-drilled winter crop under decent sowing conditions, the spring wheat margin was almost twice the level of the September-drilled wheat and it gave a huge advantage in the blackgrass legacy for the rotation.

“Overall, our research really underlines that sowing flexibility is what you really need for your bad blackgrass ground. First and foremost don’t sow it early. Make sure you stimulate and Roundup-off [glyphosate] as many flushes of weed growth as you can before you put your wheat in,” he said.

Mr Lloyd advises growers to plan to drill from the second half of October. But if they can’t get a good enough seed-bed, they should not be tempted to maul it in and hope for the best.

Instead, he suggest to work the ground up when growers can and drill the wheat into the best possible conditions in the spring. Then keep the winter wheat seed safely in the shed for the next autumn.

“The chances of a season in which conditions prevent you successfully sowing both later winter and spring wheat are very small. And in such a year it may be better not to waste your money on a crop at all and make the most of a well-managed fallow,” he said.

Mr Lloyd said that every 100 ears/sq m of blackgrass knocks 1t/ha off wheat yields and will add many hundreds of thousands of extra seeds to the ground. He is adamant that the long-term gain from intelligent, flexible management can be well worth a considerable amount of short-term pain.