Scald is common disease of

barley Barley (''Hordeum vulgare''), a member of the grass family, is a major cereal grain grown in temperate climates globally. It was one of the first cultivated grains, particularly in Eurasia as early as 10,000 years ago. Globally 70% of barley pr ...

in temperate regions. It is caused by the fungus ''

Rhynchosporium ''Rhynchosporium'' is a genus of fungi that causes leaf scald disease on several graminaceous hosts. It includes five currently accepted species: '' R. secalis'' from rye and triticale, '' R. orthosporum'' from ''Dactylis glomerata'', ' ...

commune'' and can cause significant yield losses in cooler, wet seasons.

Symptoms

Scald is a foliar disease of barley affecting the leaves and sheaths of the plant; however, lesions may also occur on

coleoptile Coleoptile is the pointed protective sheath covering the emerging shoot in monocotyledons such as grasses in which few leaf primordia and shoot apex of monocot embryo remain enclosed. The coleoptile protects the first leaf as well as the growing ...

s, glumes, floral

bracts In botany, a bract is a modified or specialized leaf, especially one associated with a reproductive structure such as a flower, inflorescence axis or cone scale. Bracts are usually different from foliage leaves. They may be smaller, larger, or of ...

and awns. Initial symptoms 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 A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from th ...

can infect and survive in barley seed. It exists as

mycelium Mycelium (plural mycelia) is a root-like structure of a fungus consisting of a mass of branching, thread-like hyphae. Fungal colonies composed of mycelium are found in and on soil and many other substrate (biology), substrates. A typical single ...

in the pericarp and hull of infected seeds. Infection of the coleoptile occurs as it emerges from the embryo. Optimal infections occur at soil temperatures of 16C. At soil temperatures of 22C or higher, very little infection occurs. In spring cropping systems, the fungus

overwinters Overwintering is the process by which some organisms pass through or wait out the winter season, or pass through that period of the year when "winter" conditions (cold or sub-zero temperatures, ice, snow, limited food supplies) make normal activi ...

on the crop debris and stubble of previous diseased barley crops. The fungus produces abundant

conidia A conidium ( ; ), sometimes termed an asexual chlamydospore or chlamydoconidium (), is an asexual, non-motile spore of a fungus. The word ''conidium'' comes from the Ancient Greek word for dust, ('). They are also called mitospores due to the ...

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 In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, f ...

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 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.Rhynchosporium
Scottish Agricultural College. In the

Victoria Victoria most commonly refers to: * Victoria (Australia), a state of the Commonwealth of Australia * Victoria, British Columbia, provincial capital of British Columbia, Canada * Victoria (mythology), Roman goddess of Victory * Victoria, Seychelle ...

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. In Canada, yield losses in

Alberta Alberta ( ) is one of the thirteen provinces and territories of Canada. It is part of Western Canada and is one of the three prairie provinces. Alberta is bordered by British Columbia to the west, Saskatchewan to the east, the Northwest Ter ...

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 Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in c ...

area on the flag and second leaves resulting in reduced seed weight.Agriculture and Rural Development - Scald
, Government of Alberta.

Management

Management of the disease involves the use of clean and/or treated seeds, resistant cultivars, crop rotation, residue management, and foliar

fungicide Fungicides are biocidal chemical compounds or biological organisms used to kill parasitic fungi or their spores. A fungistatic inhibits their growth. Fungi can cause serious damage in agriculture, resulting in critical losses of yield, quality, ...

Resistant cultivars

Cultivars A cultivar is a type of Horticulture, cultivated plant that people have selected for desired phenotypic trait, traits and when Plant propagation, propagated retain those traits. Methods used to propagate cultivars include: division, root and st ...

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,

cyproconazole Cyproconazole is an agricultural fungicide of the class of azoles, used on cereal crops, coffee, sugar beet, fruit trees and grapes, on sod farms and golf courses and on wood as a preservative. It was introduced to the market by then Sandoz in 19 ...

¹, epoxiconazole¹, fluquinconazole¹, flusilazole¹, propiconazole^{1, 2, 3}, prochloraz¹, pyraclostrobin², tebuconazole¹ Seed treatment fungicides: triadimenol² 1. Registered for use in Europe.
2. Registered for use in Canada.
3. Registered for use in the US.Plant Disease Control - Scald
{{webarchive, url=https://archive.today/20120715052657/http://plant-disease.ippc.orst.edu/factsheet.aspx?RecordID=112 , date=2012-07-15 , Oregon State University Extension.

Fungicide resistance

In the United Kingdom, there are issues concerning MBC fungicides and some of the triazole fungicides (e.g.

flusilazole Flusilazole (DPX-H6573) is an organosilicon fungicide invented by DuPont, which is used to control fungal infections on a variety of fruit and vegetable crops. It is moderately toxic to animals and has been shown to produce birth defects in high d ...

and

epoxiconazole Epoxiconazole is a fungicide active ingredient from the class of azoles developed to protect crops. In particular, the substance inhibits the metabolism of fungi cells infesting useful plants, and thereby prevents the growth of the mycelia (funga ...

). To date there are no issues with

strobilurin Strobilurins are a group of natural products and their synthetic analogs. A number of strobilurins are used in agriculture as fungicides. They are part of the larger group of QIs (Quinone outside Inhibitors), which act to inhibit the respiratory ch ...

fungicides (QoI fungicides), but the situation is being monitored closely. There are currently no issues concerning chlorothalonil, cyprodinil or the morpholines.

References

Fungal plant pathogens and diseases Barley diseases