.

Date: August 3, 2007
Source:
Farmers Guardian [edited]
<http://www.farmersguardian.com/story.asp?sectioncode=19&storycode=11743>

Take-all tracking at the Home Grown Cereals Association [HGCA] Recommended List 2nd cereal trial sites across the country has revealed infections taking off in a major way this summer. So much so that the average disease level ahead of this year's [2007] harvest has reached its highest since routine NIAB [National Institute of Agricultural Botany] root assessments began 3 years ago.

At just under 10.0, the average take-all index recorded at GS31 this season was very similar to that seen in both 2005 and 2006. While disease levels only built-up gradually to an index of 17 by GS39, the warm and very wet summer prompted infections to develop apace, with the index reaching an average of 46 by GS75. This compares with a final index averaging around 25 last season [2006] when disease development was restricted by the very dry summer and 37 in the moderately high take-all year of 2005.

What is more, severe take-all infections indexing more than 60 were recorded on 4 of the 10 sites compared to just one in 2005, with high to very high levels on a further 2. With 2005 records showing control variety yields suffering by as much as 3.5 t/ha under severe infection conditions, this is clearly worrying for many 2nd wheats sown without a take-all seed treatment last autumn [2006].

"Actually the most worrying thing probably isn't the effect of the generally very high disease levels on this year's [2007] yields," said study coordinator, David Leaper of Monsanto. "While the root systems of severely affected crops will have been badly compromised by the rapid spread of infections this summer, the continued wet conditions throughout the past month means they haven't exactly had to cope with much in the way of drought stress. Of course, persistent severe water-logging may be particularly harmful to crops with compromised root systems, but for most growers the yield impact of whatever take-all they have in their crops is likely to be noticeably less than in a very dry late summer."

By far the greatest impact of this season's very high levels of infection is likely to be seen in the coming year [2008], he says. Higher than normal levels of inoculum will be carried over to infect this autumn's plantings.
At the same time, high reservoirs of both moisture and warmth in the soil will provide ideal conditions for early disease development, as will any damage to soil structure from what is shaping up to be a hugely difficult harvest.

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ProMED-mail
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[Take-all is a fungal disease causing severe yield loss of up to 50 per cent in cereal crops. _Gaeumannomyces graminis_ var. _tritici_ causes disease in wheat and barley, _G. graminis_ var. _avenae_ affects oats, _G.
graminis_ var. _maydis_ affects maize, and _G. graminis_ var. _graminis_ affects a range of grasses. _G. graminis_ var. _tritici_ was 1st recognised in Australia in 1852 and is considered the most serious root disease of cereals worldwide.

Take-all symptoms are rotting of the roots and lower stems. Severe disease development is indicated by stunted plants with whitened stems and spikes.
When infection occurs early in the crop cycle, the number of tillers is often reduced and spikes may be sterile. The fungus persists on crop debris in the soil and appears to be restricted to temperate wheat-growing areas.
Volunteer cereal plants and grasses may serve as pathogen reservoirs.
Infection can occur throughout the crop cycle. The disease is favoured by cool (12-18 deg C / 53.6-64.4 deg F) soil temperatures, alkaline or nutrient deficient soils, nitrate, and minimum tilling practices.

Disease management includes fungicides, crop rotation, and other cultural practices such as moderate planting density and weed control. No varieties of wheat or barley exist with specific resistance to take-all. Disease severity is expressed as take-all index (TAI), which is calculated as the proportion of nodal root systems with symptoms.

Growth stages for cereals are measured by a decimal code (Zadok's scale).
GS30-39 refer to the stem elongation stage, GS70-79 to the kernel and milk development stage.

Map of the UK:
<http://www.lib.utexas.edu/maps/europe/united_kingdom.gif>
Pictures
Root symptoms on wheat:
<http://www.plantmanagementnetwork.org/php/elements/view.asp?ID=1>
Symptoms on seed heads of wheat:
<http://www.plantmanagementnetwork.org/php/elements/view.asp?ID=224>
Field with take-all patch:
<http://www.plantmanagementnetwork.org/php/elements/view.asp?ID=223>
Links
Take-all information, including more pictures:
<http://www.plantmanagementnetwork.org/pub/php/diagnosticguide/take-all/>
Disease information and control strategies:
<http://www.takeall.com/english/default.htm#options>
Disease epidemiology and take-all index:
<http://www.apsnet.org/phyto/pdfs/2001/0423-01R.pdf>
_G. graminis_ var. _tritici_ taxonomy:
<http://www.indexfungorum.org/Names/NamesRecord.asp?RecordID=352824>
_G. graminis_ var. _avenae_ taxonomy:
<http://www.indexfungorum.org/Names/NamesRecord.asp?RecordID=352823>
_G. graminis_ var. _maydis_ taxonomy:
<http://www.indexfungorum.org/Names/NamesRecord.asp?RecordID=358215>
_G. graminis_ var. _graminis_ taxonomy:
<http://www.indexfungorum.org/Names/NamesRecord.asp?RecordID=429590>
Growth stages of cereals:
<http://www.grdc.com.au/GRDC/ResearchSummaries/CMAttachments/cropmonitoringv2.pdf> 

Home Grown Cereals Association UK:
<http://www.hgca.com/>
NIAB website:
<http://www.niab.com/>.  - Mod.DHA]

[see also in the archive:
2000
---
Take-all disease, wheat - Australia (02) 20001021.1822 Take-all disease, wheat - Australia 20001017.1779]

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