Take-all could be particularly troublesome for second cereal growers this season, warns Monsanto.
Records from HGCA Recommended List second cereal sites show a heavy build-up of take-all infections for the second year in a row (see table).
Given the persistently wet soils ideal for the disease’s development this poses a serious threat to second cereals, even in sowings well into October and beyond, says the firm’s Rob Plaice who co-ordinated the monitoring.
Averaging 61 on a 1-100 scale, the take-all index in the CEL second wheat trials this summer was the highest recorded since routine NIAB root assessments began in 2005, he notes.
Severe infections – over index 60 – were recorded on 63% of sites. In last year’s high take-all season the figure was only 40%.
Two of the worst sites were so badly infected they were not taken to official yield. And control yields on the three other severely infected sites averaged 8.8t/ha (3.6t/acre) against the10.4t/ha (4.2t/acre) overall trial mean.
“These results confirm that take-all has built up substantially from the high levels of infection recorded in our 2007 monitoring,” says Mr Plaice.
The crops had full fungicide programmes but no take-all seed treatment, highlighting the losses the disease can cause without adequate safeguards, he adds.
“While the wet summer once again enabled many crops with quite badly compromised root systems to survive without excessive yield loss, it also allowed the fungus to continue proliferating widely.”
Soils damaged during the difficult harvest and very wet seed-beds this autumn provide ideal conditions for early take-all development.
So, unless the risk from the disease has historically been very low, all growers drilling wheat or barley as a second cereal should use a seed treatment against take-all – regardless of variety or drilling date, he urges.
Delaying drilling until mid-October helps reduce take-all risk. But inoculum levels are so high and conditions so favourable for early infection that it is unlikely to prevent serious damage, especially if next winter is mild and wet, Mr Plaice believes.
“The fact that all but one of last season’s CEL second wheat trials were sown after 11 October and the one most affected by take-all wasn’t drilled until 16 November underlines the extent of the continued risk.
“And independent trials in East Yorkshire have shown an average yield response of over 1t/ha from Latitude treatment of Einstein and Gladiator sown in the first week of December.”
Take-all levels at second wheat CEL variety trial sites 2005-2008
Average take-all index (GS65-75)
* Take-all Index of 60 or more
Getting to the root of takeall problems
Trials to find out why some varieties perform better than others as second wheats have ended. But the joint work, by ADAS and NIAB from 2004 to 2006, confirmed that some indeed do, so HGCA Recommended List data in that respect can be relied on.
The experiments, part of the Rothamsted Research led Wheat Genetic Improvement Network, compared three renowned good second wheat performers with three varieties poorly suited to that rotational slot.
All were grown as first and second wheats in the same field with and without take-all inoculation.
The average yield decline between first and second wheats – as reflected in RL data – was about 1t/ha (0.4t/acre).
“But a poor second wheat, such as Robigus, can lose as much as 2t/ha more than a relatively consistent performer such as Cordiale,” says NIAB’s Rosemary Bayles.
The research confirmed that while take-all severity is a key contributor to yield loss, varietal tolerance is equally if not more important in reducing the disease’s impact.
“It confirms that growers should be reassured that RL data do pick out the second wheat winners and losers,” says ADAS’s Neil Paveley.
“Robigus, for example, is widely recognised as a poor second wheat. The work showed it’s no more susceptible to take-all than other varieties, but it’s intolerant to infection – with greater loss of yield per unit of disease than the others.”
Napier tolerated take-all much better, producing higher yields, and Cordiale appeared to have some resistance, notes Dr Paveley.
The mechanisms of tolerance and resistance could not be confirmed, but he rules out the influence of cereal cyst nematode or eyespot – both at negligibly low levels in the trials.
Differences in rooting could account for the differences, he speculates, the more resistant varieties having fewer contacting the pathogen which spreads to the plants from soil debris.
“However, it’s clear from the breeding perspective, that there are opportunities to improve second wheat performance by introducing traits from types such as Cordiale and Napier.
“The amount of disease seen in a variety though is not the whole story. We also need to work with the best sources of tolerance to improve varieties.”
Resistance in wild grasses could also eventually be introduced into wheats. “But this is a long, hard job.”
Dr Bayles notes that the £40,000 DEFRA-funded project focused on just six varieties.
“This was so that we could investigate in detail just what makes a variety a good second wheat,” she says. “As new varieties come on stream we expect to identify others which perform well in that situation.
“On the current RL, Battalion appears to do particularly well as a second wheat, with Einstein, Marksman, Duxford, Humber, Gladiator and Cordiale also looking useful.
“We need to get a handle on the genetics of second wheat performance. So we’re disappointed that we’ve been unable to secure funding to continue this work as it could help speed the breeding of varieties more suited to that slot.”
First wheat build-up
The risk of severe take-all occurring in wheat largely depends on the amount of inoculum in the soil at sowing, says Rothamsted’s Richard Gutteridge.
“Four year’s data from the WGIN experiments show that varieties can differ in their ability to build up the take-all fungus when grown as a first wheat.”
Although there is limited information on current varieties more work is planned to cover all on the RL, notes Mr Gutteridge.
“Preparing for a first wheat is important as any survival of the fungus will accelerate build up,” he says.
Break crops should be free of cereal volunteers and other grass carriers of the fungus and phosphate and potash supplies must be adequate, at index 2, to create conditions least favourable for the fungus.