Diseases

In some respects New Zealand is fortunate when it comes to the diseases infecting wheat and barley. While the impact can be devastating if not controlled, the number of different diseases to understand is quite small.

Wheat is attacked by four key diseases: Septoria leaf blotch, stripe rust, leaf rust and tan spot, with a small number of diseases of lesser importance, powdery mildew  and a number of ear diseases, Fusarium ear blight, glume blotch and sooty moulds.

Barley is attacked by just four diseases: Scald, net blotch, Ramularia leaf spot and powdery mildew. 

Choose your crop to find out more detail

Septoria leaf blotch

Septoria leaf blotch (also known as speckled leaf blotch, Septoria tritici, Zymoseptoria leaf blotch and Mycosphaerella graminicola) is a common disease of wheat and can be found anywhere in the world where wheat is grown, including New Zealand.

Disease incidence

In some parts of the world, especially Northern Europe, infection by Septoria leaf blotch can almost be guaranteed due to the wet and relatively mild winter weather. In other parts of the world though, including New Zealand, infection from Septoria leaf blotch is more sporadic. 

Within New Zealand Septoria leaf blotch can be expected to infect wheat crops most years in Southland but in Canterbury it is more of a seasonal disease. In Canterbury, there was a prolonged period when Septoria leaf blotch was hard to find. Then in around 2010 it suddenly became a major problem. For a number of years after that it was the key disease of wheat causing significant yield losses when not controlled. But then a couple of years ago it began to fade away again.

Now though, in 2016, it looks to be back with sporulating lesions present in April planted crops.

Septoria Leaf Blotch Wheat Arable Fungicides Bayer

It is still unclear why the disease behaves in the way it does but it is likely to be due to a combination of the wheat varieties being grown, climatic factors, earlier planting and a reduction in the effectiveness of strobilurin and DMI fungicides. Visit this page for more information on Resistance Management. Whatever the reason for the varying infection pressure from Septoria leaf blotch, the best approach is to not take any chances. To assume it could be there and to walk your paddocks regularly.

The time to look for Septoria leaf blotch is between August and flag leaf emergence. During this period Septoria leaf blotch is relatively easy to identify due to the black pycnidia (spores) visible with in lesions. 

Septoria Leaf Blotch Wheat Arable Fungicides Bayer

And keep looking! 2015 was generally a low incidence year for Septoria leaf spot, but in a Bayer trial at Aorangi on the lower North Island the level of Septoria infection level was very high. Also, infection came in around flag leaf emergence which is much later than normal.

“When I walked into the paddock at Aorangi in late November 2015 I was really surprised to see the severe Septoria leaf blotch infection in the Bayer trial and surrounding paddock. It was the worst Septoria I have seen in the 10 years I have been in New Zealand, and equal to the disease levels I used to experience in England.” Neil Waddingham,  Marketing Manager for Arable crops.

Septoria Leaf Blotch Wheat Arable Fungicides Bayer

Identification and impact

Septoria leaf blotch is a relatively straight forward disease to identify with the dark fruiting bodies being a diagnostic factor. The disease also tends to grow between the leaf veins resulting in long, narrow lesions. These lesions tend to coalesce and can develop sufficiently to kill the leaf.

Septoria leaf blotch is a very damaging disease with yield losses of 40-50% regularly recorded in New Zealand and overseas trials.

(Aviator Xpro) helped us achieve yields averaging between 8 and 12 tonnes per hectare; over the 64 ha of wheat we grew here last season.

Graeme Marshall, Darfield

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Life cycle

The life cycle starts in the autumn soon after harvest. In early autumn Septoria leaf blotch spores are released from fruiting bodies called pycnidia on the previous season’s stubble. Spore release continues for a long period of time but the main spore release occurs during late March – early May and it is crops emerging during this period that are most at risk.

Once Septoria leaf blotch has infected a crop it develops within the crop. This period, from infection to when the disease can be seen on the crop is called the latent period and it can take a long time. The latent period is temperature dependent and in the colder winter months it can take many weeks for the disease to complete a life cycle.

Once lesions can be found on the crop the disease cycle starts again only this time the spores are already in the crop and as temperatures are tending to increase, each disease cycle tends to be shorter than the last one.

From GS30, once the crop starts to elongate, two main disease transfer mechanisms occur.

The one often referred to, but which tends to happen relatively infrequently, is rain splash. If heavy rain occurs, raindrops can splash Septoria leaf blotch spores throughout the crop canopy allowing the disease to easily and quickly infect all of the emerged leaves. Although an effective mechanism for disease spread, it is actually quite uncommon for this to be the main way Septoria leaf blotch infects within a crop.

The most common way Septoria leaf blotch infections occur within crops is through physical transfer. The upright stature of modern wheat crop canopies means that infected lower and older leaves are often physically higher in the canopy than the newly emerging, uninfected leaves. All it needs is wind and moisture, from a heavy dew or irrigation, to allow leaves to rub together and for Septoria leaf blotch spores to spread, germinate and survive long enough to infect healthy leaves.

Septoria Tritici

Risk factors

Planting date

Spores “lift off” in early autumn over a relatively short period of time which means that crops with a high risk of infection are those that emerge from March through to mid-May.

This doesn’t mean crops that emerge after mid-May aren’t at risk, just that the risk diminishes the later a crop emerges. In Bayer trials this has been seen many times with crops essentially free of Septoria leaf blotch infections in the spring going on to be heavily infected by Christmas if not treated with a fungicide programme. 

This appears to be the case in the Bayer trial conducted at Aorangi on the lower North Island in spring 2015. Even though infection occurred relatively late it was still very severe leading to yield loss.

SEPTORIA TRITICI

Variety choice

While different varieties show different susceptibilities to Septoria leaf blotch, even the most resistant varieties cannot protect themselves. Choosing a more resistant variety always makes sense if other factors allow, but only use variety susceptibility values as a guide, do not rely on them.

It was visually easy to see a response… the Aviator area was noticeably greener.

Sam Grant, Methven, mid Canterbury

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Spring weather

Analysing over 30 years of farm information, researchers in the United Kingdom have identified wet spring weather as being the most important factor determining severe disease outbreaks. It is likely to be same here in New Zealand with wet springs, between early October and mid-November, being the key risk factor.

Septoria Tritici

Control of Septoria leaf blotch

If Septoria leaf blotch has been identified as a risk to your wheat crops at GS29-30 then applying Aviator Xpro will provide excellent control.

Apply a programme of Aviator Xpro at 1.0 L/ha at GS31-32 and again at GS37-39 and you will effectively control not only Septoria leaf blotch but also any stripe rust or leaf rust in the crop.

N.B. It is important that the time interval between your GS31-32 and GS37-39 applications is less than 28 days.

Septoria Tritici

Stripe rust (Puccinia striiformis f. sp. tritici)

Identification and Impact

Until recently stripe rust was the main disease threat to wheat crops. When stripe rust infects early in the season it can be very difficult to identify from early leaf rust infections as at this time the stripe rust spores are not usually arranged in stripes, rather as randomly arranged spores. Stripe rust spores are yellower than leaf rust spores, which tend to be browner, but this is hard to differentiate in the field.

An uncontrolled stripe rust infection can be very damaging with yield losses of 30% often recorded in Bayer New Zealand trials.

Life Cycle

Stripe rust is favoured by cool, moist conditions and crops severely infected with the disease were a common sight. So what has changed in recent years?

Again, the reasons aren't exactly known but it likely to be due to combination of the wheat varieties being grown, climatic factors and the widespread use of Galmano seed treatment. Galmano provides very effective control of stripe rust through until spring, by which time spring fungicides are applied. By keeping the crop free of stripe rust during the winter it makes it so much harder for the disease to get established later in the year.

Once stripe rust infects a crop it can develop very quickly with each disease cycle taking around 7-10 days. This gives it the potential to devastate crops. While disease development slows down as temperatures rise, it is often cold and wet enough in New Zealand for the disease to develop throughout the spring, even infecting the ear of susceptible varieties in some seasons.

Risk Factors

Geography

While stripe rust infection can occur throughout New Zealand, the disease tends to have favoured locations where infection takes place most years. If you live in one of these areas, your own experience will tell you this and you will be looking out for the disease each season.

Variety Choice

Globally there are a number of distinct strains of stripe rust. Varietal breeding ensures that new varieties are resistant to the majority of these strains and often this is sufficient to allow a variety to essentially remain free of the disease for a number of years. Eventually though, a stripe rust strain that can infect a “resistant” variety arrives in New Zealand and the “resistant” variety gets infected as severely as other varieties.

Although it is after just one season, I‘ve found that both Aviator Xpro and Prosaro have done a good job at keeping the Septoria at bay.

Andrew West, Mid-Canterbury

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Control of stripe rust

Control is straight forward as adopting a robust fungicide programme incorporating Aviator Xpro, Proline or Prosaro will control the disease. The programme outlined below will provide very effective stripe rust control.

N.B. Whatever fungicide programme you adopt it is important that the time interval between your GS31-32 and GS37-39 applications is less than 28 days.

Leaf rust (Puccinia triticina)

Leaf rust is a disease favoured by warm days and cool nights. The disease develops at temperatures between 15oC and 22oC hence the requirement for warm days but it needs high humidity for the spores to germinate and infect the plant, hence the need for cool, dewy nights.

Leaf rust survives on volunteer plants and from these wind-borne inoculum can infect the crop. This sometimes occurs in the autumn but usually it is in the spring. Leaf rust symptoms are of a loose pattern of brown pustules on the leaf.

Life Cycle

The life cycle of leaf rust is short, probably only taking a few days under optimal conditions and so infections can develop very quickly if not controlled and significant yield losses can occur.

Control of leaf rust

Control is straight forward as adopting a robust fungicide programme based on Aviator Xpro, Prosaro or Proline, as outlined on the Best Use page, will control the disease. The programmes below will not only control leaf rust but also Septoria tritici and stripe rust as well. Make your decision based on the Septoria tritici pressure you face as both programmes will control leaf rust.

The importance of good leaf rust control was graphically illustrated in a Bayer Crop Science North Island trial carried out in 2015. In the untreated, 2 weeks after the ear fungicide had been applied, there was already greater than 40% leaf rust infection. In this trial a comparison was made between a two spray fungicide programme (GS32 and GS39) and a three spray fungicide programme (GS32, GS39 and GS60) - as illustrated below). The three spray fungicide programme gave 95% leaf rust whereas this fell to 40% with a two spray fungicide programme and this reduction in leaf rust control resulted in a yield loss of 3.5 t/ha!

If Septoria tritici lesions can easily be found at GS32, with the majority of plants infected, then a programme based upon a GS32 application of Aviator Xpro at 1.0 L/ha, followed by a second spray of Aviator Xpro at GS39 (flag leaf emerged), again applied at 1.0 L/ha, with a final application of Prosaro or Proline applied at GS59, ear emerged, will provide very good control.

Alternatively if your Septoria tritici pressure is much lower it makes sense to retain your two Aviator Xpro applications to later as this is when we have seen the highest yield increases from applying Aviator Xpro. In this case a GS32 application of Prosaro at 1.0 L/ha or Proline at 500 ml/ha followed by Aviator Xpro applied at 1.0 L/ha at both GS39 and GS59 will give you very effective disease control.

N.B. It is important that the time interval between your GS32 and GS39 applications and your GS39 and GS59 applications is less than 28 days.

Tan spot (Pyrenophora tritici-repentis)

Identification and Impact

Tan spot was first recorded in New Zealand in 1979 as a seed borne pathogen, but subsequently foliar infections were found. 

Initial lesions on the lower leaves are small, brown in colour with a distinct yellow border. Later on the upper leaves the lesions are larger, elliptical to diamond shaped, still with a yellow border but now also with a dark centre. Eventually these lesions coalesce to form large tan coloured lesions.

Under suitable conditions tan spot can have a major economic impact with yield losses of up to 30% recorded. In 2015 in Canterbury, a trial* conducted by a combination of FAR, PLANTwise and NZ Arable, demonstrated a yield loss of 1.68 t/ha, or 28%, in what was a moderately yielding crop.

*The control of tan spot of wheat (caused by Pyrenophora tritici-repentis: a possible emerging disease in New Zealand. I.C. Harvey, R.A. Craigie and B.L. McCloy. 2015 New Zealand Plant Protection Society (Inc.) www.nzpps.org

Lifecycle

Tan spot spores are released from infected crop debris in early spring and if adequate moisture is available infection takes place. The first lesions develop around 1 week after infection. Tan spot is favoured by warm wet weather with temperatures between 20-250C being ideal. When weather conditions are conducive to disease development it can occur very quickly.
Control is straight forward as adopting a robust fungicide programme incorporating Aviator Xpro will control the disease (Aviator Xpro is the only New Zealand fungicide to be registered for the control of tan spot). A programme based on Aviator Xpro will not only control tan spot but Septoria leaf blotch, stripe rust and leaf rust as well.

Powdery mildew (Blumeria graminis f.sp. tritici)

Identification and Impact

Powdery mildew is a disease most people recognise. Initially seen as small, surface patches of white, fluffy mycelium, powdery mildew can develop to coat the entire leaf. As the infection matures small, black cleistothecia can often be seen.

Under suitable conditions, powdery mildew can have a major economic impact with yield losses of up to 40% recorded.

Lifecycle

Powdery mildew thrives in cool, cloudy and moist conditions when temperatures are between 12-200C. Disease development can be rapid under suitable climatic conditions.

Control of powdery mildew

Powdery mildew isn’t a difficult disease to control as long as a fungicide is applied at the early signs of disease development. As powdery mildew develops largely on the leaf surface effective control usually results in the return of a healthy leaf.

Fusarium ear blight (Fusarium spp.)

Identification and impact

Fusarium ear blight is caused by a number of different Fusarium species and while symptoms differ in detail they all result in the death of part of the ear – from the death of a single spikelet to a large part of the ear.

Fusarium infection can have a severe economic impact through a combination of reduced grain size, poor grain quality and mycotoxin production by the fungus.

Lifecycle

Although the infection mechanism of Fusarium ear blight isn’t fully understood it is likely to be due to the direct transfer of spores from crop debris to the ear through a combination of wind and rain. Infection is favoured by warm, wet weather, especially heavy storms, during flowering.

Control of Fusarium ear blight

Best practice is to apply a fungicide effective against Fusarium species around GS55-60.

Ear blight of wheat (Monographella nivalis)

This disease has changed its name at least twice over the past 80-90 years. Initially known as Fusarium nivalis it then became known as Microdochium nivalis before changing again to Monographella nivalis in recent years.

Identification and impact

Initial disease symptoms consist of small, brown, water-soaked lesions on the outer glumes of florets. Under humid/wet conditions florets, entire spikelets and even entire ears can become infected and bleached. 

Infection of the leaves can also occur in which case quite large, irregular brown lesions develop.

Infection by Monographella ear blight results in small, shriveled grain leading to reduced yields and lost value.

Lifecycle

This disease is active over a very witd temperature range between –60C and 320C but with an optimum range of 18-200C. Ear infection results from both rain splashed and wind dispersed spores during flowering.

Control of Monographella ear blight

DMI fungicides such as Prosaro or Folicur or DMI/Strobilurin fungicides such as Delaro provide good control of ear blight.

Glume blotch (Stagonospora nodorum)

Identification and impact

The most common and visible symptoms are dark patches, often purplish in colour, on the glumes.

In most situations the economic impact on yield is moderate but high yield losses have been observed occasionally from severe infections.

Lifecycle

The disease survives both on the seed and on crop debris. Glume blotch infection results from spores produced on crop debris when conditions become warm and humid in early summer. The life cycle is rapid taking just 10-14 days.

Control of glume blotch

An application of Folicur, Prosaro or Delaro between GS59-69 will protect against glume blotch.

Sooty moulds (Cladosporium spp. and Alternaria spp.)

Identification and impact

As the name suggests infection by sooty moulds leads to soot like deposits on the ear which eventually result in the ear turning a dark colour. 

Infection by sooty moulds doesn’t generally result in large yield losses but discolouration of the grain can reduce the commercial value of the grain and make it harder to sell.

Lifecycle

Sooty moulds are caused by infection of a number of different, weak pathogens. Wind borne spores for these diseases form a common component of the air and they infect ears when the conditions are suitable – warm, humid weather being ideal. Often, infection is associated with white heads resulting from stem base diseases.

Control of sooty moulds

An application of Folicur or Prosaro at the latest time allowed by the withholding period will protect against sooty mould infection.

N.B. Whatever fungicide programme you adopt it is important that the time interval between your GS31-32 and GS37-39 applications and between GS 37-39 and GS59-69 applications are each less than 28 days.

The barley fungicide programme illustrated below will provide excellent control of the main barley diseases in New Zealand. To see fungicide programmes tailored to specific barley situations click here.

Ramularia leaf spot

Ramularia leaf spot (Ramularia) is found throughout the world where barley is grown and climatic conditions favour the disease. It is a particular problem in New Zealand, Scotland and parts of Europe.

The disease only infects barley, whether it is winter or spring barley.

The typical symptoms of the disease are small, brown lesions, rectangular in shape with a yellow halo, at least at first, but they often coalesce and can rapidly kill the leaf when conditions favour the disease.

The life cycle of the disease starts with the seed. Ramularia can be found on the seed. From here it infects the plant and for most of the life of the disease it grows within the plant without showing any symptoms. However, after flowering the disease expresses the symptoms described above and can rapidly and prematurely kill a crop leading to significant yield loss.

The reasons the disease expresses itself are not fully understood but are thought to involve either a physiological trigger, e.g. the transfer of stored sugars from the stem to the developing grain, a stress trigger or that the fungus produces the toxin rubellin D, which can cause oxidative damage under the right light conditions. One other risk factor that has been identified is leaf wetness at stem extension, GS30.

Although Ramularia tends to reduce green leaf area towards the end of the plants natural life it can still significantly reduce yield with up to 11% yield loss recorded in Bayer trials from not controlling a moderate infection.

Ramularia

Control of Ramularia involves adopting several strategies.

As there isn’t any evidence that seed treatments control the disease it is important to start with healthy, certified seed. Varieties do differ in their susceptibility to Ramularia and if possible a variety with a high tolerance score should be chosen, but variety tolerance should only be seen as minor part of the disease control approach.

Ramularia

It is then important to keep your crop as healthy as possible by applying a good nutritional regime, rigorous weed control and a robust fungicide programme at GS25-30 and again at GS31-32 for winter planted barley or at GS25-30 for spring planted barley. This allows your crop to maximise food production in the early spring and to store this in the stem well before Ramularia symptoms appear.

The most important action though is applying Aviator Xpro at 1.0L/ha at GS37-45. SDHI containing fungicides have been shown to be the most effective against the disease but it important to ensure that more than one mode of action is applied. Aviator Xpro contains the two most effective barley fungicides, the DMI prothioconazole and the SDHI fungicide bixafen.

Bayer provided our entire seed treatment, weed and disease control program – including its newly launched fungicide Aviator® Xpro.

Warren Darling, South Canterbury

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Scald (Rhynchosporium secalis)

Traditionally in New Zealand scald is the major disease of barley. The disease can also infect other crops such as grass species, triticale and ryecorn but in these cases it is by specialised forms of the fungus.

Scald symptoms first appear in winter on the foliage, often as quite indistinct brown “smudgy” type lesions. Later in the spring the disease continues to infect the leaves but it can also attack the stem and ear. At first, lesions are pale green with a “watersoaked” appearance, but as these mature they often develop a dark brown margin with a paler brown “bleached” appearance. Lesions can coalesce to form large infected areas and often spores are washed down into the leaf axils where they produce quite large lesions. These lesions have the ability to kill the entire leaf.

The disease is seed borne but crop debris and volunteer plants are likely to be the primary sources of scald. Spread within the crop is then mainly by rainsplashed spores.

Under mild, wet conditions the disease can develop rapidly if an effective fungicide programme isn’t applied. Adopting a fungicide programme based on Delaro and Aviator Xpro will not only effectively control scald, but also Ramularia leaf spot as well. 

Apply Delaro at a rate of 750 ml/ha at GS31-32. Then apply Aviator Xpro at 1.0 L/ha at GS39-45.

We applied both Aviator Xpro and Prosaro by ground spraying and there was no sign of disease in either the wheat or barley.

Andrew Gillanders, Central Canterbury

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Net blotch (Pyrenophora teres f. teres)

Net blotch can infect many species of grass but the form that infects barley is specific to barley and doesn’t infect other species.

Net blotch produces a range of symptoms varying from just a brown stripe on the first leaf through stripe like symptoms to the typical symptom of net blotch, lesions with a brown net like appearance. There is also a form of net blotch called spot blotch where the lesions are oval in shape.

Net blotch normally infects the leaves but it can also infect the glumes and awns. In this case it shows as dark flecking and striping.

Net blotch infection occurs from either infected seed or from debris from the previous crop. If seed-borne mycelium infect the coleoptile of the plant and the first leaf to emerge becomes infected, however, the most common source of infection is crop debris. Inoculum from crop debris is splash-borne up and between plants. This is why second year barley crops usually show the highest level of infection.

The lower leaves of a barley plant play an important role in producing the crop’s yield. Net blotch is favoured by cool, wet conditions giving it the potential to severely infect crops early in the spring. It is therefore easy to see why net blotch can resulting in significant loss of yield if left untreated.

Net Blotch

Adopting a fungicide programme based on Delaro and Aviator Xpro will effectively control net blotch as well as scald and Ramularia leaf spot as well.

Apply Delaro at a rate of 750 ml/ha at GS31-32. Then apply Aviator Xpro at 1.0 L/ha at GS39-45.

It was the first time I’ve ever seen a crop of barley senesce naturally rather than die off due to disease and it was beautiful grain to harvest.

Ian Batchelor, North Canterbury

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Leaf rust (Puccinia hordei)

Leaf rust is a disease favoured by warm days and cool nights. The disease develops at temperatures between 15oC and 22oC hence the requirement for warm days. However, it needs high humidity for the spores to germinate and infect the plant, hence the need for cool, dewy nights.

Leaf rust survives on volunteer plants and from these wind-borne inoculum can infect the crop. This sometimes occurs in the autumn but usually it is in the spring. Leaf rust symptoms are of a loose pattern of brown pustules on the leaf.

Leaf Rust

The life cycle of leaf rust is short, probably only taking a few days under optimal conditions and so infections can develop very quickly if not controlled, and significant yield losses can occur.

Leaf Rust

Adopting a robust fungicide programme based on Delaro and Aviator Xpro will control the disease. The programmes below will not only control leaf rust but also scald, net blotch and Ramularia leaf spot.

Apply Delaro at a rate of 750 ml/ha at GS31-32. Then apply Aviator Xpro at 1.0 L/ha at GS37-45.

Powdery mildew (Blumeria graminis f.sp. tritici)

Identification and Impact

Powdery mildew is a disease most people recognise. Initially seen as small, surface patches of white, fluffy mycelium, powdery mildew can develop to coat the entire leaf. As the infection matures small, black cleistothecia can often be seen.

Under suitable conditions, powdery mildew can have a major economic impact with yield losses of up to 40% recorded.

Lifecycle

Powdery mildew thrives in cool, cloudy and moist conditions when temperatures are between 12-200C. Disease development can be rapid under suitable climatic conditions.

Control of powdery mildew

Powdery mildew isn’t a difficult disease to control as long as a fungicide is applied at the early signs of disease development. As powdery mildew develops largely on the leaf surface effective control usually results in the return of a healthy leaf.

The barley fungicide programme illustrated below will provide excellent control of the main barley diseases in New Zealand. To see fungicide programmes tailored to specific barley situations click here.