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Date: 24 Jun 2007
[1] Powdery mildew, sugar beet: alert
[2] Ramularia leaf spot, barley: alert

[1] Powdery mildew, sugar beet: alert
Source: Farming UK [edited]
<http://www.farminguk.com/index.asp?show=newsArticle&id=3990&country=>

Powdery mildew is by far the most yield-damaging disease in sugar beet, causing up to 20 per cent yield loss. It adversely affects yield by draining the plant of nutrients, reducing root growth, increasing plant respiration, reducing green leaf area, and blocking photosynthetic pathways. It will reduce yield and suppress sugar content, particularly on later-drilled crops. This is particularly so on susceptible varieties, which now represent at least half of the crop in the ground this year [2007], warns Dow AgroSciences.

"More that 80 per cent of sugar beet crops receive a mildew treatment and that is where the focus should be, particularly this year [2007]. Broom's Barn [the UK Sugar Beet Research Centre] are already warning growers that it will be a high mildew year, with 40 per cent of the crop predicted to become infected by the end of August [2007]. Incorporating a strong, persistent mildew-specific fungicide into any sugar beet programme as the cornerstone will ensure effective control of this damaging foliar disease and help optimise the resulting crops' yield potential," says Liz Tomkinson, fungicide specialist for Dow AgroSciences.

"The extent of the powdery mildew epidemic each year depends upon the number of ground frosts in February and March. The disease overwinters on groundkeeper crowns, wild beet or beet volunteers and so the lower the number of frosts, the greater the amount of inoculum that is available to infect newly drilled crops. If the weather is warm and dry in July and August, then powdery mildew is likely to arrive earlier, starting in East Anglia. Growers should be out looking for disease and be prepared to apply a fungicide at the 1st signs of disease. If rusts or _Ramularia_ also become a problem, normally later in the season and usually much more sporadically, a tank-mix of fungicides is a flexible option and resulted in the highest yields in the 2006 Broom's Barn trials, as well as in the previous 4 years independent trials work," reports Tomkinson.

"With growers looking to maximise yields and profits, a comprehensive 2-spray fungicide has become the norm, particularly on high output varieties with low mildew and rust resistant ratings. With the EU sugar scheme taking effect, growers need to make the most from their sugar beet hectarage and get more of their quota out of a smaller area of land.
Appropriate fungicide usage will make an important contribution to yields and gross margins," concludes Tomkinson.

--
communicated by:
J Allan Dodds
Former ProMED-mail plant disease moderator <dodds@ucr.edu>

[2] _Ramularia_ leaf spot, barley: alert
Date: Mon 4 Jun 2007
Source: Farming Views [edited]
<http://www.farmingviews.co.uk/landwriter/premium/TemplateParser.asp?aId=7410>

The growing incidence of the barley disease, which causes yield-sapping leaf spotting, has led the HGCA [Home Grown Cereals Association UK] to produce a new set of advice for growers.

"Growers should review spring barley losses due to _Ramularia_ in recent years to decide if current crops need treatment," said professor Graham Jellis, director of research, pointing out that a method of predicting the disease is currently being researched.

The disease is now common in northern Britain where it is the greatest threat to malting barley spring crops, but the HGCA says it can occur UK-wide. Symptoms to look for are small brown rectangular lesions with yellow margins within leaf veins. Lesions occur on both green and dead leaves, with brown spots remaining visible on dead leaves.

The HGCA says a forecast is being developed based on region, variety, weather (rainfall and leaf wetness), and presence of spores, which will help growers determine the risk of crop loss from this spreading disease problem. Where treatment is considered necessary on the basis of past experience, the HGCA is recommending a preventative spray before symptoms appear.

"Prevention with fungicides is most effective when applied at boot stage to awns peeping (GS45-49) [see comment below for explanation], provided applications are made before symptoms appear, usually after the crop has flowered. _Ramularia_ is not controlled by seed treatments," said Prof Jellis. "Fungicides applied at tillering also have little impact on disease control.

Spring barley varieties show different levels of resistance, but no variety is fully resistant and yield losses range from 0.9 t/ha in Optic, down to
0.1 t/ha in Decanter. The average yield loss in high disease risk sites is
0.4 t/ha. _Ramularia_ can also impair quality and increase screenings [undersized grains that are lost at harvest].

--
communicated by:
J Allan Dodds
former ProMED-mail plant disease moderator
<dodds@ucr.edu>

[Powdery mildew on sugar beet is caused by the fungus _Erysiphe betae_. It occurs worldwide and also infects other beet crops, such as beetroot. It is a serious foliar disease with reported sugar yield losses of up to 30 per
cent. The fungus is an obligate parasite requiring a living host for growth and reproduction, and therefore is spread with living infected tissue. Symptoms start on the lower leaves and disease development is favoured by a
wide fluctuation in day-night temperatures. Unlike other powdery mildews, _E. betae_ has so far received relatively little attention and the precise mechanisms by which it infects its host remain unclear.

Sources of genetic resistance have been identified in cultivated and wild _Beta_ germplasm and a number of resistant sugar beet varieties are available.

The other sugar beet fungi referred to in this news item are _Ramularia beticola_ causing leaf spot, and the rust _Uromyces betae_.

_Ramularia collo-cygni_ causes symptoms on barley including small brown rectangular lesions with yellow margins within leaf veins. Strong sunlight, prolonged leaf wetness, agrochemical scorch, and nutritional stress can all
trigger physiological leaf spots associated with infections by the fungus. The fungus may also affect some other cereals and grasses and is spread via infected plant material and wind, but its epidemiology is not completely
known yet.

_Ramularia_ leaf spot is present in central Europe, South and Central America, and New Zealand. It poses the greatest threat to spring malting barley and resistant varieties are being developed. It is less common on winter barley, which, however, can act as a source of inoculum for the spring crop.

Growth stages on barley are defined by a 2-digit code system. GS45 identifies the "boot" stage where the head becomes prominent within the flag leaf sheath; at GS49, the 1st awns are visible.

Maps
UK:
<http://www.lib.utexas.edu/maps/europe/united_kingdom.gif>
Location of East Anglia:
<http://en.wikipedia.org/wiki/East_Anglia>
_Ramularia_ distribution in Europe:
<http://www.bba.bund.de/cln_045/nn_813794/DE/Aktuelles/aktschadorg/ramularia/verbreitung.html>
Pictures
Powdery mildew symptoms on sugar beet
- comparison of healthy and affected leaf:
<http://www.ag.ndsu.edu/pubs/plantsci/pests/pp967-1.jpg>
- on whole plant:
<http://www.dowagro.com/uk/images/powdery-mildew-in-sugarbeet.jpg>
_Ramularia_ symptoms on barley
- individual leaf:
<http://wwwuser.gwdg.de/~rcc/assets/rcc-bestand2.jpg>
- whole plant:
<http://www.darcof.dk/enews/newsmail/november_2006/figures/rls.jpg>
Links:
Sugar beet powdery mildew information:
<http://www.bspp.org.uk/publications/pathprofiles/pathprofile14.htm> and
<http://www.ag.ndsu.edu/pubs/plantsci/pests/pp967w.htm>
Broom's Barn:
<http://www.rothamsted.bbsrc.ac.uk/broom/sbrindex.php>
_Erysiphe betae_ taxonomy:
<http://www.indexfungorum.org/Names/SynSpecies.asp?RecordID=330695>
Barley _Ramularia_ information:
<http://www.hgca.com/document.aspx?fn=load&media_id=3505&publicationId=3847> 
and via
<http://wwwuser.gwdg.de/~rcc/index.htm>
_Ramularia collo-cygni_ taxonomy:
<http://www.indexfungorum.org/Names/SynSpecies.asp?RecordID=133476>
Explanation of growth stages of barley:
<http://www.extension.umn.edu/distribution/cropsystems/DC2548.html>
Home Grown Cereals Association UK:
<http://www.hgca.com/>. - Mod.DHA]

[see also in the archive:
Fungal pathogens, wheat - United Kingdom: new races 20070523.1652
2004
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Powdery mildew, sugar beets - USA (NE) 20040825.2375]

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