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News archive 1997-2008

Fungal diseases on oilseed rape and maize in the United Kingdom

A ProMED-mail post

<http://www.promedmail.org>

ProMED-mail is a program of the

International Society for Infectious Diseases <http://www.isid.org>

[1] Oilseed rape: phoma, light leaf spot
[2] Maize: eyespot

[1] Oilseed rape: phoma, light leaf spot

Date: Fri 16 Oct 2009

Source: Farmers Guardian [edited]

<http://www.farmersguardian.com/news/arable/arable-news/little-change-in-phoma-predictions-but-lls-risk-higher/28365.article>

The 1st signs of phoma infections are appearing in oilseed rape crops slightly later than usual this autumn [2009] across the country as a whole. However, backward crops, particularly in the East, will be more at risk from the disease. And bad weather during harvest in the North means the predicted onset of phoma into crops is earlier this year, says Dr Neal Evans, plant pathologist at Rothamsted Research.

"As you come further south into Lincolnshire and Nottinghamshire growers will be seeing 10 percent phoma leaf spotting now in their crops, which follows a similar pattern to last year [2008]," he says.

Preliminary predictions for light leaf spot show increased levels in crops compared with forecasts for 2008/09 in the North, East Midlands, and West, however crops in the South West may get less disease than last season. "Inoculum has been building up generally over the past few seasons because of wet weather, and there is more light leaf spot out there as a result," says Dr Evans.

"Light leaf spot is very crop specific and you can get high infestation on one farm and no sign of it in the next. It's very affected by, and dependent upon, rain and with the increasing pattern of localised downpours that we seem to be getting, it can be a very specific problem." Crops should be sprayed for light leaf spot when

25 percent of plants are affected.

Communicated by:

ProMED-mail

<promed@promedmail.org>

[2] Maize: eyespot

Date: 16 October 2009

Source: Farmers Guardian [edited]

<http://www.farmersguardian.com/news/livestock/infection-%E2%80%98not-as-bad-as-was-first-feared%E2%80%99/28336.article>

For those who have already harvested their maize, Simon Pope, of Wynnstay, is recommending they bury stubble soon to reduce eyespot infections in next year's [2010] maize crop. Incidences of infection in this year's maize crop are less widespread than at first feared, says Dr Pope, but where disease took hold, yield losses of up to 80 percent were reported.

"Eyespot has been a significant problem for growers in the south west of England but it is slowly spreading across southern England and into South Wales," he says. "Carmarthenshire and Pembrokeshire have become real hotspots for the disease with growers reporting significant yield losses. Cold, wet seasons provide ideal conditions for the spread of the disease." Dr Pope recommends considering this when selecting varieties.

Communicated by:

ProMED-mail

<promed@promedmail.org>

[Light leaf spot (LLS) of _Brassica_ species is caused by the fungus _Pyrenopeziza brassicae_. Leaves become infected soon after sowing, but remain symptomless until lesions appear on older leaves.

Developing pods are often infected, leading to premature ripening of seed and pod shatter. LLS is polycyclic and survives the summer on crop debris, volunteer oilseed rape, and vegetable brassicas. Disease management includes varieties with decreased levels of susceptibility, disease monitoring, and timely fungicide applications. In the UK, LLS has caused considerable yield losses of oilseed rape in the past and was reported in 2009 to be at its highest level since the epidemic of 1995 (ProMED-mail post 20090226.0795).

Phoma leaf spot and stem canker (blackleg) is caused by the fungus _Leptosphaeria maculans_. It is considered the most serious disease of oilseed rape with a possible yield loss of 50 percent or more. It can also affect other _Brassica_ hosts such as cabbage and turnip.

Symptoms on rape may include lesions on leaves, stems, and pods, with stem cankers leading to premature ripening or collapse of the crop.

However, symptomless infections may also occur. The fungus is seed-borne and is also spread by wind, splash dispersal, and infected crop litter. It may overwinter in stubble, which is therefore often sprayed with fungicides. Disease management includes use of clean seed, cultural practices to minimise inoculum, fungicides, and planting of resistant cultivars. The pathogen is extremely diverse with new strains evolving frequently some of which have overcome major resistance genes within certain varieties in the past.

Eyespot of maize is caused by the fungus _Kabatiella zeae_. Leaf symptoms include lesions with a light coloured centre and a brown margin ('eyespots'). Symptoms may include early drying out of the leaves, shrivelling of the ears, and even kernel infections. Eyespot can lead to considerable yield reduction and also predisposes the host to stalk rots. Host susceptibility is highest during cold rainy seasons. The fungus is specific to maize and can overwinter in plant debris. Spores are dispersed by rain and wind, and the disease may be carried over in stubbles from the previous years maize crop. Disease management includes deep ploughing (to encourage decomposition of crop debris), crop rotation, and fungicide treatments. Hybrid maize lines with reduced susceptibility are available.

Maps of UK:

<http://www.lib.utexas.edu/maps/europe/united_kingdom.gif> and <http://healthmap.org/r/008E>

Pictures

LLS symptoms on oilseed rape:

<http://cropmonitor.csl.gov.uk/wosr/encyclopaedia/view_iImage.cfm?id=46>

(leaves),

<http://www.sac.ac.uk/mainrep/images/winteroilseedrape?view=Standard>

(leaves), and

<http://www.rothamsted.ac.uk/ppi/pics/llsp_lge.jpg> (pods) Phoma leaf spot on oilseed rape:

<http://www.apsnet.org/Education/LessonsPlantPath/BlacklegCanola/text/fig05.htm>

Rape planting with blackleg:

<http://www.apsnet.org/education/LessonsPlantPath/BlacklegCanola/images/fig07.jpg>