A ProMED-mail post
<http://www.promedmail.org>
ProMED-mail is a program of the International Society for Infectious Diseases <http://www.isid.org>

Date: 2 October 2008
Source: Farming UK [edited]
<http://www.farminguk.com/news/A-high-disease-pressure-year-for-brassica-growers8697.asp>

With the continuing wet, warm, and humid conditions, specialist agronomist John McCulloch of County Crops considers this year [2008] to be a particularly high-pressure year for a number of diseases.
Advising growers in the North West, he says that he has seen more sclerotinia this year than ever before. "I have seen a lot of it in the usual crops such as lettuce, celery, carrots, and oilseed rape [see recent ProMED-mail posts below] and also in some more unusual crops such as calabrese [broccoli variety]. These high levels can be put down to this year's terrible weather and high rainfall, which have encouraged sclerotinia as well as other wet weather diseases including ring spot (_Mycosphaerella brassicola_), white blister (_Albugo candida_) and _Botrytis_," says John.

John advises growers to adopt an appropriate fungicide programme, but with fungicide resistance and crop safety being top of mind. "This means starting fungicides early. They can be mixed as part of a resistance strategy and then followed by other fungicides with different modes of action. Use fungicides only when necessary. It is so important to minimise any resistance pressure on any one-fungicide group. We already have resistance to metalaxyl in _Botrytis_,"
advises John. He points out that there are fewer and fewer effective products from which to choose. "If the EU decides to limit this any further, we could be in a very difficult situation. It is vital that we retain the armoury of products that we have."

--
Communicated by:
ProMED-mail
<promed@promedmail.org>

[The disease referred to is the fungus _Sclerotinia sclerotiorum_. It is one of the most nonspecific and successful of plant pathogens with around 400 known hosts and is present worldwide.

Symptoms vary on different hosts, for example: On celery the disease is called pink rot because the rotted, watery area that develops on mature celery is usually pinkish in color; the fungus attacks the basal crown and petioles; plants appear to suddenly wilt and collapse in the field. On lettuce, the disease is called lettuce drop; outer leaves are infected first, then the fungus moves inward; leaves wilt and fall from the head in succession; the heart may remain erect, but becomes a wet, slimy mass. On beans, pods can become infected, while on the plant and post harvest. On carrot, it causes severe root rot and also affects the leaves. For disease description on oilseed rape see previous reports. On some crops, the related species _S. minor_ can cause similar symptoms.

The pathogen is primarily soil-borne and has a complex disease cycle.
It can survive in soil as sclerotia and is also spread by infected plant material, mechanical means, and wind-borne spores. Risk of crop infection depends on the previous disease history of an area as well as weather conditions. Disease management includes cultural practices and fungicide applications.

The report above makes an important point on guarding against build-up of fungicide resistances in pathogens of crops. New fungal strains evolve frequently adapting to environmental pressure. Modern crop monocultures provide ideal conditions for pathogens and therefore for the emergence of new strains with increased virulence and increased resistance traits.

Maps of the UK:
<http://www.lib.utexas.edu/maps/europe/united_kingdom.gif> and <http://healthmap.org/promed?v=53.167,-0.25,5>

Pictures
Sclerotinia on lettuce:
<http://ag.arizona.edu/PLP/plpext/diseases/vegetables/lettuce/lettsclero4.htm>
<http://ag.arizona.edu/PLP/plpext/diseases/vegetables/lettuce/lettsclero7.htm>
Pink rot of celery:
<http://postharvest.ucdavis.edu/Produce/ProduceFacts/Veg/celeryPinkRot-sm.gif>
_S. s._ on carrot:
<http://www.gov.mb.ca/agriculture/crops/horticulture/report/07-09-28/07-09-28carrotsclerotinia.jpg>
(roots),
<http://www.actpub.co.uk/uploadimages/1181137685-vegstory125.png>  (leaves)
Stained microscopy of _S. sclerotiorum_ sexual spores:
<http://ag.arizona.edu/PLP/plpext/diseases/vegetables/lettuce/lettsclero1.htm>

Links
Information on _S. sclerotiorum_:
<http://www.extento.hawaii.edu/kbase/Crop/Type/s_scler.htm>,
<http://anrcatalog.ucdavis.edu/pdf/8042.pdf>  and <http://www.cals.ncsu.edu/course/pp728/Sclerotinia/S_sclerotiorum.html>
Sclerotinia on carrots:
<http://www.organicagcentre.ca/ResearchDatabase/res_carrots_canopy.asp>  and <http://www.abdn.ac.uk/web/test/organic/research/sclerotinia_advice.php>
Pink rot of celery:
<http://vric.ucdavis.edu/veginfo/topics/disease/PinkCelery.pdf>
Lettuce leaf drop:
<http://ag.arizona.edu/PLP/plpext/diseases/vegetables/lettuce/lettuceld.htm>
Sclerotinia of oilseed rape (with pictures):
<http://www.agric.wa.gov.au/pls/portal30/docs/FOLDER/IKMP/FCP/CO/PW/BULLETIN4406A.HTM#sclerotinia>
and
<http://www.hgca.com/publications/documents/cropresearch/Topic77.pdf>
_S. sclerotiorum_ taxonomy:
<http://www.indexfungorum.org/Names/NamesRecord.asp?RecordID=212553>. 
- Mod.DHA]