- Scald (barley)
Scald is common disease of barley in temperate regions. It is caused by the fungus
Rhynchosporium secalis and can cause significant yield losses in cooler, wet seasons.cite book
last = Mathre
first = D.E.
title = Compendium of barley diseases
publisher = American Phytopathological Society
date = 1997
pages = 120 pp ] cite book
last = Martens
first = J.W.
coauthors = W.L. Seaman, T.G. Atkinson
title = Diseases of field crops in Canada
publisher = Canadian Phytopathological Society
date = 1984
pages = 160 pp ]Symptoms
Scald is a foliar disease of barley affecting the leaves and sheaths of the plant, however, lesions may also occur on coleoptiles, glumes, floral bracts and awns. Initial sympotms are oval, water-soaked, grayish-green spots, 1.0-1.5 cm long. As the disease develops, the centers of the lesions dry and bleach, becoming light gray, tan, or white. with a dark brown margin. The lesions are not delimited by the leaf veins and often coalesce.
Disease cycle
The fungus can infect and survive in barley seed. It exists as mycelium in the pericarp and hull of infected seeds. Infection of the coleoptile occurs as it emerges from the embryo. Optimal infections occurs at soil temperatures of 16C. At soil temperatures of 22C or higher, very little infection occurs.
In spring cropping systems, the fungus overwinters on the crop debris and stubble of previous diseased barley crops. The fungus produces abundant conidia on wet lesions during cool, damp weather after the leaf tissue has become necrotic. Conidia, spread by wind and splashing rain, infect young leaves of spring- planted grain. Optimum temperatures for sporulation and infection range from 10-18C. Hot, dry weather reduces the rate of disease development.
Geographical distribution and economic importance
The disease is economically important barley disease in Europe, North America and Australia. It has been reported from South America, Africa, the Middle east, Japan and Korea. Yield losses as high as 35-40% have been reported, however, losses of 1-10% are more common. Yield loss is primarily due to reduced kernel weight, but both kernels per head and number of heads per plant may also been affected.
In the wetter areas of the United Kingdom, scald is the most damaging disease of barley, affecting both spring and winter crops. [http://www.sac.ac.uk/consultancy/cropclinic/clinic/diseases/rhynchosporium Europe: Scotland] ] . In the Victoria area of Australia, scald is widespread in barley crops in most seasons, but its severity varies greatly from crop to crop and between seasons. In Victoria, scald causes annual average yield losses of 10-20%, with individual losses as high as 45% in susceptible varieties. [http://www.dpi.vic.gov.au/dpi/nreninf.nsf/childdocs/-22C871BE2A0105794A2568B30004D413-3C5B474B480825C8CA256BC700824574-78F1BBD6496F89034A256DEA00274EEC-491BE1EC936D69A3CA256C170004772F?open Australia] ] In Canada, yield losses in Alberta have been calculated at 2.4 per cent, although losses in particular fields may exceed 25 per cent. Losses are due to a decrease in photosynthetic area on the flag and second leaves resulting in reduced seed weight. [http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/prm2427 Alberta yield losses] ]
Management
Management of the disease involves the use of clean and/or treated seeds, resistant cultivars, crop rotation, residue management, and foliar fungicides.
Resistant cultivars
Cultivars with scald resistance are available in all major barley growing areas. The level of resistance occurs along a spectrum and the degree of resistance that is required to effectively control the disease will depend on the region where it is grown, cropping practices that reduce initial disease inoculum, wetter conditions and fungal pathotypes.
Fungicides
Foliar fungicides can be used to effectively control disease development. Product selection, application rates and timing, depend upon numerous factors.
The availability of fungicides as a management tool depends on whether the product has been evaluated and registered for use in a specific country or region.
Foliar fungicides: azoxystrobin1, bromuconazole1, cyproconazole1, epoxiconazole1, fluquinconazole1, flusilazole1, propiconazole1, 2, 3, prochloraz1, pyraclostrobin2,tebuconazole1
Seed treatment fungicides: triadimenol2
1. [http://209.85.165.104/search?q=cache:odp29TY_Ee8J:archives.eppo.org/EPPOStandards/PP2_GPP/pp2-11-e.doc+barley+diseases+eppo&hl=en&ct=clnk&cd=4&gl=us EPPO - Europe]
2. [http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/prm2427 Canada: Alberta]
3. [http://plant-disease.ippc.orst.edu/disease.cfm?RecordID=112 US: Oregon]Fungicide resistance
Wikimedia Foundation. 2010.
