Delaying wheat drilling on bad black-grass ground for little more than a month can improve margins and reduce future weed problems dramatically, according to latest results from the country’s leading black-grass management trials site. And if conditions don’t favour late winter wheat sowing, the work shows the spring alternative offers substantial performance improvements in both respects too.

In the Agrii studies on heavy land with some of the country’s most challenging black-grass populations at Stow Longa near Huntingdon,  Solstice sown on November 1 yielded an average 7.76t/ha over a range of cultivation systems last harvest to generate a £903/ha margin over input costs. In contrast the same variety sown at the same seed rate across the same range of cultivation systems on September 27 averaged just 4.82 t/ha with a margin of £389/ha.


What’s more, delaying drilling for the four weeks cut black-grass levels by an order of magnitude, from more 200 the ears/m2 to less than 20 ears/m2, reducing the weed seed return massively.


“All our detailed establishment system research over the past four years shows highly significant improvements in yield and reductions in black-grass from delaying drilling,”
Agrii national agronomy manager, Colin Lloyd told more than 150 growers visiting the site at a late June open day.  “This takes a huge amount of pressure off post-em herbicides, in particular. Which is just as well, as the best black-grass control we’re getting with 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 black-grass. You need to give enough time for weed seedlings to emerge so you can hit them with Roundup 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 black-grass. And the more flushes you can stimulate and spray-off ahead of sowing the better.


“Yes, delaying drilling is a risk,” Colin Lloyd accepted.  “If conditions turn against you on the sort of ground on which you invariably get the worst black-grass it may mean you can’t get a decent crop of winter wheat at all. 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 altogether with the sprayer later on. The choice is yours.”


Actually, the Agrii work at Stow Longa shows that leaving the worst black-grass ground for later drilling needn’t be nearly as risky it may seem. Indeed,  parallel trials with six Group 1 and 2 spring wheats sown on April 4 last year in the next door field with equally high black-grass levels delivered an average of 6.46 t/ha with a £729/ha margin and a weed population of zero ears/m2.


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 black-grass legacy for the rotation (Figure).


“Overall, our research really underlines that sowing flexibility is what you really need for your bad black-grass ground,” insisted Mr Lloyd.


“First and foremost don’t sow it early. Make sure you stimulate and Roundup-off as many flushes of weed growth as you can before you put your wheat in. Plan to drill from the second half of October. But if you can’t get a good enough seedbed, don’t be tempted to maul it in and hope for the best. Instead, work the ground up when you can and drill your wheat into the best possible conditions in the spring. Then keep your winter 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 suggested.


At Stow Longa, Colin Lloyd knows that every 100 ears/m2 of black-grass knock 1 t/ha of wheat yields and add many hundreds of thousands of extra seeds to the ground. So he is adamant that the long-term gain from intelligent, flexible management can be well worth a considerable amount of short-term pain.

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