Barley - Diseases

On this page:

• Head and root diseases
• Foliar diseases

Diseases occur when a susceptible host is exposed to a virulent pathogen under favourable environmental conditions.  Control is best achieved by knowledge of the pathogens involved and manipulation of the interacting factors.  Little can be done to modify the environment but growers can minimise the risk of diseases by sowing resistant varieties and adopting practices to reduce inoculum.

Resistant varieties provide the easiest and most effective option; yet few varieties possess adequate resistance to all major diseases.  Alternative strategies are therefore required to reduce risk.  Rotate barley crops with non-hosts such as wheat (to control foliar pathogens), legumes or summer crops; avoid sowing barley on barley and maintain clean fallows.  Sowing out of season favours disease development and can build up inoculum early in the season.

The main foliar diseases of barley are leaf spots, rusts and powdery mildew.  Leaf spots and powdery mildew over season on crop residues while rusts (and to a lesser extent powdery mildew) require living plants to carry them from one season to the next.

Growers should assess the disease risk of individual paddocks before sowing.  Consider the recent history of a paddock, the incidence of diseases in recent barley crops and the amount of infected stubble in the target and neighbouring paddocks.  Infected stubble can usually be recognised by the prescence of small black "pimples" on the straw.

Head and root diseases

Crown rot (Fusarium psuedograminearum) is common in winter cereals. It is soil-borne and can be carried  over from one season to the next on barley and wheat stubble.  A barley variety with the same rating as a wheat vaareity will not suffer the same level of yield loss, however yield losses as high as 28%  have been recorded. Rotation with chickpeas or summer crops is currently the best method of controlling crown rot as there are no varieties which possess adequate field resistance.

Covered smut (Ustilago hordei) is seed-borne and has a life cycle similar to bunt of wheat. Grain contaminated with covered smut is not accepted by end users, unless heavily discounted. Smuts can be easily controlled with seed dressing, and barley seed should be treated for smut every year.

NOTE: Seed treatments are available for control of:

• Covered and loose smuts 
• Seed borne net blotch (net form)
• Seed borne spot blotch
• Powdery mildew (up to eight weeks protection)

    

Common root rot (Cochliobolus sativus) is also soil-borne. It is widespread in barley crops and may cause yield losses of up to 15%.  As there are no varieties resistant to this disease, rotation with summer crops or winter legumes is the best method of control.

See a summary of fungicide seed treatments registered for smut.
See barley variety characteristics table for information on variety resistance to diseases.

Black point in barley

Black point is a dark discolouration at the germ end of otherwise healthy barley grain. Yellowing of the germ end of the grain is probably also a variation of black point discolouration.. The discolouration occurs in the glume tissue (palea and lemma) which remains adhered to the outer seed coat. The conditions that cause high levels of black point in wheat often do not cause any discolouration in barley. The precise nature and timing of the environmental stresses that induce black point symptoms are not fully understood, however, yield, humidity and temperature are likely to be involved.

Black point causes a slight reduction in the rate of germination but without a significant effect on the malting process. However, in combination with shrivelling, field mould or disease, grain health may be affected and germination rates reduced. Little information is currently available on varietal resistance levels in barley.

Root Lesion Nematode (Pratylenchus thornei). Barley is tolerant to root lesion nematode infection and is therefore a good winter cropping option in infested areas. Although barley is more tolerant than many wheat varieties and most varieties are resistant to very resistant, nematode numbers in the soil may still increase under barley cropping. Rotations using resistant crops are encouraged.

		Tolerance	Resistance
	Tallon	VT	R
	Grimmett	T	R
	Lindwall	VT	-
	Gairdner	-	MR
	Schooner	-	MR
	Gilbert	VT	-
	Kaputar	T	-
	Skiff	VT	MR

• Tolerance refers to the ability of the plant to sustain yield under high levels of nematode infestation. (VT = Very Tolerant; T = Tolerant)
• Resistance refers to the inability of the nematodes to increase in number during the growth of the crop. (R= Resistant; MR= Moderately resistant)

Barley - Foliar diseases

Barley foliar disease reference table

The following table outlines the common foliar diseases and the basic information on survival dispersal infection times and control options.

Leaf rust

Stem rust

Leaf rust (Puccinia hordei)and stem rust (Puccinia graminis tritici, secalis and tritici x secalis ) are traditionally the major air-borne diseases of barley in Queensland and are more likely to occur in wetter years or higher rainfall areas. Both can cause significant yield loss and quality downgrading. Grain yield can be reduced by up to 50% by stem rust and around 30% by leaf rust. As stem rust may infect barley and wheat, an epidemic could put both crops at risk.  The best protection from either disease is to plant resistant varieties and avoid planting very early or very late in the season. Barley occupies approximately 25% of the winter cereal area; therefore as long as resistance levels of all winter cereals (especially wheat) remain high it is not expected that major epidemics of stem rust will occur in barley.  In emergencies timely application of fungicides can be effective.

'Net' form of net blotch

'Spot' form of net blotch

Net blotch (Pyrenophora teres) has become the most significant disease of barley in the region and is likely to be a problem in wetter years and in stubble-retained situations. The pathogen may also be seed-borne.

It occurs in two forms – net form of net blotch (P teres f. teres) and spot form of net blotch (P. teres f. maculata). The net form produces dark brown to black stripes on leaves and leaf sheaths of older plants and gives a characteristic netting pattern in juvenile leaves. The spot form of net blotch produces dark brown, round to elliptical spots on leaves and leaf sheaths that are often surrounded by yellowing.  High levels of either disease will kill leaves prematurely which may cause yield losses in excess of 30%. Growers are advised to avoid planting barley on barley where stubble is retained, as stubble-borne spores are the main source of infection for the new crop.

The net form of net blotch may be seed borne and grain from heavily diseased crops should not be retained for planting.

Spot blotch

Powdery mildew

Spot blotch (Cochliobolus sativus) is favoured by warm wet conditions and is promoted by stubble retention. It can be seed borne. Leaf symptoms are almost identical to the spot form of net blotch yet spot blotch may also cause discolouration of grains. This disease is more likely to be a problem in sub-coastal areas. Popular varieties are susceptible.

Barley Grass Stripe Rust (Puccinia striiformis) was recorded in crops of Skiff in northern New South Wales in 1999 but as very few sightings have occurred since, it is unlikely to be a major problem in the northern region in the near future.

Powdery mildew (Blumeria graminis hordei) is often present in susceptible varieties, but generally causes only relatively small yield loss (usually less than 10%). Some seed treatments can give good early season control of powdery mildew but these may also shorten coleoptile length and cause emergence problems. Resistant varieties are the best means of control.

Some varieites may appear susceptible at the seedling stage but develop adult plant resistance.  Where this occurs lower leave of infected plants may take on a blotchy appearance after jointing.  this can be confused with other blotches.  Where powdery mildew is responsible fien mycelium is usually evident on the older leaves.

Barley seed treatment per tonne of seed for control of smuts, spot blotch and net blotch include (currently under permit held by Grainco Australia):

Liquid:    2.5 l Vitaflow plus 850mL Thiraflow®
Dry:        1.25 kg Vitavax ® plus 640g thiram WP® (not the granular form).

See the barley variety characteristics table for information on varietal resistance.

Last updated 13 July 2005