Dormancy rate makes seed-bed strategy difficult
Warm, damp conditions should be ideal for pre-drilling blackgrass germination, but seed dormancy could throw up a few surprises, as James Andrews discovers
Stale seed-bed strategies could be hard to call this autumn following the release of blackgrass dormancy trials results.
Samples from the 52 HGCA-funded study sites indicate dormancy will be “medium” with 37% of this year’s seed expected to chit, says James Clarke, head of sustainable crop management for ADAS.
“We normally get high or low dormancy, so there is a bit more uncertainty than normal,” he says. “We don’t expect either very rapid or very slow emergence of seed shed this year. But it is possible it could be a couple of weeks later than a low dormancy year.”
Dormancy is the time it takes for seeds to germinate, with high dormancy taking the longest, he explains. “It is determined during plant maturation, which usually occurs between mid June and mid July in blackgrass.”
Hot and dry conditions at this time usually delivers low dormancy and high autumn germination, whereas cold and damp tend to give the highest dormancy, says Mr Clarke. “In 2010 it was cold in the first half of this period and hot at the end, which could explain why dormancy is medium.”
Last season blackgrass dormancy was higher, with just 23% of seed shed that year expected to germinate. Dry autumn conditions meant germination from the seed bank, which contained seeds from a number of seasons, didn’t geminate until late in some cases.
But this season’s relatively damp harvest means blackgrass in the seed bank is likely to emerge earlier, giving plenty of time to take plants out in stale seed-beds, he says.
“Growers should spray off any blackgrass that does emerge before drilling. There should be opportunities this year, assuming there will be adequate moisture.”
Ploughing should be considered for fields with high blackgrass populations, but if control has been very effective in this seasons crop growers should be careful to avoid unearthing more weed seeds than they bury. “It has been the second year of relatively poor blackgrass control, but ploughing could still bring up more serious problems from previous years.”
Leaving seeds buried for three to four years before ploughing back is advisable, he says. “You get an 80% population declining every year, so you shouldn’t have many viable seeds after this time. Ploughing up seeds after just two years can bring up problems.”
Growers should aim to get a competitive crop where blackgrass populations are high, he explains. “Keep seed-rates up and avoid cloddy seed-beds to maximise herbicide performance and reduce risk of late-emerging blackgrass.”
Any blackgrass that does emerge later in the established crop will be much less competitive, meaning control strategies should be autumn-focussed, he says. “Based on two year’s monitoring, high dormancy did not, in winter crops, lead to a spring flush of blackgrass.”
Yorkshire AICC agronomist Patrick Stephenson has not yet seen blackgrass emerging in stubbles, but reckons there is still time to remove considerable numbers. “If it was a low dormancy year I would expect to see a bit about by now, but it’s still worth creating a stale seed-bed and getting as much to germinate as possible.”
Harvest was starting to drag in the areas due to the damp weather, but there should still be time to get a chit, he says. “We should have a month’s weather to achieve germination in a stale seed-bed.”
Case Study: Edd Banks, Harlton, Cambridgeshire
Achieving good stale seed-beds is top priority for eastern Barometer farmer Edd Banks from Manor Farm in Harlton, Cambridgeshire.
“We’ve got such a bad blackgrass problem, we need to get as much as possible to grow before drilling.”
Going in with the cultivator straight after the combine gives blackgrass a long period in which to germinate, he says. “We do our best to force it to grow and we nearly always get some to germinate, even if it’s dry.”
After dirty first wheats he is deep cultivating with his Vaderstad Top Down to get maximum soil disturbance and is following straight after with the same machine on a much lighter setting. “This levels the seed-bed and creates a fine tilth, which makes herbicides more effective. I’m hoping for good results this season as we’ve had some significant rainfall recently. We will then leave it as long as we dare before spraying off and drilling.”
The worst fields may be sprayed off and re-cultivated to get a second chit, he says. “We only do this when we really have to and we don’t always have time.”
Drilling on these patches is delayed until early or mid November and he has planted Cordiale on 2 January. “This year there has been virtually no blackgrass in the November-drilled ground, but there is a light sprinkling in the January-established crops.
All cereals are going to receive a robust pre-emergence herbicide programme and bad fields will be treated with Avadex (tri-allate) before Atlantis (iodosulfuron) later in the autumn. “We only treat 20-30% of our ground with Atlantis in the spring.”
