Cereal Diseases

What is bunt and which crop does it affect?

Bunt is a fungal disease affecting wheat ears

What does bunt cause to happen in the wheat ears?

It forms "bunt balls" instead of normal grains

How many spores can a single bunt ball contain?

2 million black spores

How is bunt primarily transmitted to new wheat crops?

It is seed-borne (infecting seed before or at drilling) but spores can also survive in dry soil

Why is there often no visible evidence of bunt until harvest?

The disease develops inside the plant and the bunt balls only appear when grain forms

What cultural practices can help prevent bunt infections in wheat seed?

Using certified or tested home-saved seed and maintaining machinery hygiene to avoid contaminating healthy seed

What is take-all and which cereals does it mainly affect?

It is a fungal root disease primarily affecting wheat, barley and oats (mainly winter drilled crops)

What are the two varieties of take-all?

Var tritici (wheat/barley) and Var avenae (wheat/barley/oats)

What does take-all cause to happen in wheat and barley?

It causes blackened roots and white dead ears

Why is take-all still a problem in spring crops?

They can carry the disease over to the next winter drilled crop

Which grass weed is a known host for take-all?

Couch grass can harbour the take-all fungus

Why do second and third cereal crops often suffer from take-all?

Soil inoculum builds up after the first cereal which infests subsequent cereal crops

How can continuous cereals eventually lead to a "take-all decline?"

After about four years of continuous cereals antagonistic soil microbes build up and suppress the fungus (bacteria in the roots excrete chemicals that are toxic to take-all)

How might delaying drilling help reduce take-all infection in second wheat?

Each week drilling is delayed (after early October) the levels of soil inoculum will decline therefore lowering disease risk

Why would avoiding second cereals help to reduce take-all pressure?

It reduces the time that take-all has to build up in the soil

Why does establishing good soil structure and seedbeds help reduce take-all pressure?

It discourages soil growth

What could you do to ensure the crop is developed enough to survive take-all when it takes hold?

Apply N and P early so the crop is as healthy as possible

Which expensive seed treatment can protect cereals against take-all?

Latitude (Silthiofam) allows for drilling two weeks earlier while reducing take-all pressure

Which foliar disease is considered the most significant for yield loss in wheat?

Septoria Tritici

What do Septoria Tritici lesions look like on wheat leaves?

They appear as blotches with many small black dots (pycnidia)

How does Septoria Tritici typically spread within and between plants?

Spores splash upwards from debris or move via wind-blown infections

What is the lifecycle of Septoria Tritici?

10 to 14 days

What weather conditions favour Septoria Tritici infection?

High relative humidity (100%), temperatures of 15-20°C, and frequent rain-splash events

Which cultural measures can reduce Septoria Tritici pressure?

Growing resistant varieties, delaying drilling, removing or burying infected trash, utilise low seed rates and optimise nutrition/pH

Why would delaying drilling help reduce Septoria Tritici pressure?

It minimises leaf area when septoria pressure is at its highest

Why should you remove/bury trash if growing a second wheat crop?

It will become infected quickly once drilled if the debris is infected

How does maintaining a low seed rate help reduce septoria pressure?

It prevents the crop becoming overly thick which can facilitate the spread of the disease

What is Septoria Nodorum and which cereal does it mainly affect?

It is a wheat-specific disease that can cause seedling blight, leaf blotch, and glume blotch

How does Septoria Nodorum spread in the field?

It overwinters in/on seed and debris; infection occurs from seed-borne inoculum, rain-splash, or wind-blown spores

When is Septoria Nodorum most common?

If the crop is drilled late in worse conditions

Which temperatures favour Septoria Nodorum spore production?

Warmer conditions at 20-27°C and 100% relative humidity

Why does Septoria Nodorum cause indirect yield loss?

It reduces the GAI of the leaf

What is the life cycle of Septoria Nodorum?

10 to 14 days

How can seed-borne Septoria Nodorum be minimised?

Using tested or certified seed and ensuring good seed hygiene to prevent contaminated seed lots

Why would removing trash from the field help reduce Septoria Nodorum pressure?

It prevents spore survival

Why may you want to decrease the seed rate to help reduce Septoria Nodorum pressure?

It will prevent too many tillers as overly thick crops can facilitate the spread of the disease

Why may you want to increase the seed rate to help reduce Septoria Nodorum pressure?

To account for any yield damage incurred by the disease

What is yellow rust?

It is a fungal disease with distinct wheat and barley varieties; it cannot move between these two cereals

Can yellow rust spread between wheat and barley?

No as it has specific varieties to each crop

Why does yellow rust often die off later in the season?

It cannot survive above about 20°C so summer heat inhibits it

Which conditions favour yellow rust infection and spread?

Temperatures of 10-15°C with about 90% relative humidity; coastal and cooler areas are high-risk

What is the main way yellow rust overwinters?

On autumn-infected crops or volunteer plants, producing wind-blown spores the following season which infect the crop

What is the life cycle of yellow rust?

7 days - short latest period and therefore spreads very quickly

What does yellow rust cause indirect yield loss?

Badly infected leaves will die and fall off - it reduces GAI of the leaf

How can a thick well-fertilised crop canopy help limit yellow rust spread?

Denser canopies slow spore movement and may discourage rapid disease progression - use a high seed rate

What cultural practices can be done to reduce yellow rust pressure?

Remove green bridges, establish hedgerows and grow varieties with high resistance

Why would removing a green bridge help reduce yellow rust pressure?

It prevents the disease from surviving overwinter

Why would establishing hedgerows help reduce yellow rust pressure?

It prevents the disease spreading between fields by blocking the wind

How does powdery mildew spread?

Via wind blown spores

What does powdery mildew look like on cereal leaves?

A whitish-gray fungal growth on leaf surfaces with a powdery appearance

Why can powdery mildew struggle to germinate on wet leaves?

Free water on the leaf surface disrupts mildew spore germination

What is the optimum temperature and humidity for powdery mildew development?

Around 15°C and 95% relative humidity (periods of dry weather)

What is the lifecycle of powdery mildew?

7 days - short latest period and therefore spreads very quickly

Where does powdery mildew overwinter?

On the infected crop, any volunteer plants and within the crop debris

Why would establishing hedgerows help reduce powdery mildew pressure?

It prevents the disease spreading between fields by blocking the wind

Why would optimising the plant canopy help reduce powdery mildew pressure?

If it is too dense then humidity will build however leaving it too thin will allow the spores to spread via wind through the crop easier

How does excessive nitrogen application increase powdery mildew risk?

It causes the plant cells towel up reducing the thickness of the cell wall which allows the fungi to penetrate more easily

What should you ensure when choosing a variety to reduce powdery mildew pressure?

It has good resistance levels

Which crop does loose smut affect?

Barley

How is loose smut transmitted in barley?

It spreads when spores from infected ears land on open flowers of healthy plants

What happens when loose smut spores land on open flowers?

They germinate and the fungus grows in to the ovary

Where does the fungus reside until barley seedlings begin to grow?

Inside the embryo of the seed where it then invades the stem as it develops and grows up to infect the grain sites

Why does loose smut not usually become visible until ear emergence?

Fungal mycelium replaces the grain sites in the ear which only becomes apparent only when the ear emerges

What cultural practices can be done to help reduce loose smut pressure?

Avoid growing barley in fields where the disease is apparent as well as maintaining good machinery/seed hygiene

Which disease (uncommon) in barley causes leaf stripes and can lead to ear-emergence failure?

Leaf stripe

How are seeds typically infected with leaf stripe?

Spores from infected leaves blow onto adjacent barley ears which contaminate the developing grains

What are the best cultural methods to control leaf stripe in barley?

Maintain good machinery/seed hygiene

Which disease of barley features "net-like" leaf lesions and overwinters on seed or debris?

Net blotch

How does net blotch spread within a barley crop?

By rain splash up the canopy

How does net blotch initially enter a barley crop?

It overwinters on seed and debris with most infections occurring from windblown spores but can originate from soil borne inoculum

What is the ideal temperature range for net blotch development?

Between 10°C and 25°C with humid conditions

Why should seeds be tested for net blotch and at what infection level is treatment recommended?

If seed infection exceeds 15% it is recommended to use a fungicidal seed treatment to protect emerging seedlings

What methods can be used to reduce net blotch pressure in barley?

- Test the seed

- Maintain good machinery/seed hygiene

- Remove/bury any trash after harvest

- Optimise plant canopy

Which barley disease has a similar life cycle to net blotch but does not carry over in seed?

Rhyncosporium

What visible effect does rhyncosporium have on barley leaves?

It forms pale leaf blotches with darker margins than reduce green leaf area and thus yield

Why does rhyncosporium cause indirect yield loss in barley?

It reduces the GAI of the leaf

Which cultural measure helps limit rhyncosporium infection in barley?

Choosing resistant varieties to reduce the chance of severe outbreaks

What is ramularia in barley and how much yield can it reduce?

A fungal disease causing up to 0.5 t/ha yield loss

What are the five "R's" of ramularia lesions?

Reddish-brown, Rectangular, Restricted by veins, Ring of yellow, and Right through the leaf

Why is maintaining good seed hygiene so important for preventing ramularia in barley?

There are no seed treatments available

What can be done to prevent clean barley seed from becoming contaminated with ramularia?

Maintain good machinery hygiene

What is ergot?

Fungal disease in cereals which causes resting bodies (sclerotia) to form in place of the grains

What happens to the sclerotia that isn't collected in the combine which forms in the grain sites due to ergot?

They drop to the ground and overwinter in the soil, germinating in the summer to produce spore releasing bodies

Why does ergot have such a big impact on the use case of the grains produced?

The sclerotia contain mycotoxins which are toxic to humans and animals. These can constrict blood vessels and cause hallucinogenic effects. Zero to low tolerance in grain produced.

Why is ryegrass especially prone to ergot?

Open flowering in rye species gives the fungus easier access to infect unpollinated florets

Which cultural measures help bury or remove ergot sclerotia?

Deep ploughing or appropriate cultivations to prevent sclerotia from germinating on the soil surface

Why would maintaining grass margins help to reduce the pressure from ergot?

Blackgrass and ryegrass can be good hosts and will catch the disease before it enters the field however these must be cut before they seed

What rotations can be more prone to ergot?

Cereal intensive

Can ergot be completely removed from certified seed?

Some small pieces of sclerotia may remain in certified seed since zero tolerance is extremely difficult but levels are usually very low

What seed treatments can be used to control ergot although it is not claimed on the label?

Triazole seed treatments

Which disease complex includes seedling blight, foot rot, and ear blight?

Fusarium complex

What distinct colour often indicates fusarium infection?

An orange or pinkish discolouration on stems, ears, or grains

What is barley seedling blight caused by?

Fusarium

What is wheat seedling blight caused by?

Fusarium and septoria nodorum

How can fusarium ear blight lead to mycotoxin issues?

Spores infect the developing grain and toxins can form in the infected kernels

How does fusarium spread up the plant to cause ear blight and infect the seed?

By rain splash

Where does fusarium overwinter?

In the seed, on crop debris, within infected crop plants or volunteers and in the soil as chlamydospores

Why is good machinery and seed hygiene essential in preventing the spread of fusarium?

Contaminated seed spreads the fungus directly to emerging seedlings

What is common eyespot and which cereals does it affect?

It is a fungal disease in wheat and barley that causes stem based browning

When do eyespot lesions develop at the stem base?

6 to 8 weeks after infection which can kill the stem base