Sugar Beet Diseases

What is the primary symptom of virus yellows in sugar beet?

Circular patches of yellowing occur across the field

Which pathogen causes rhizomania in sugar beet, and how long can it survive in the soil?

It is caused by Beet Necrotic Yellow Vein Virus (BNYVV), and the fungus vector can persist in the soil for decades.

What are the symptoms of rhizomania in sugar beet?

• Yellow foliage and elongated petioles

• Constricted tap roots which develop prolific growth of secondary root hairs

• Dark staining of vascular tissue appears inside the roots

How does rhizomania impact sugar beet yield and sugar content?

It can reduce yield by up to 70% and lower sugar content by as much as 22%.

What is the significance of the RZ1 resistance gene in sugar beet varieties?

Most varieties on the Recommended List carry RZ1, providing tolerance and partial resistance to common strains of rhizomania.

Which rhizomania strain is not controlled by the RZ1 gene?

The AYPR strain can overcome RZ1, though it remains uncommon

Which sugar beet variety has double resistance to RZ1 and RZ2 rhizomania genes?

Osprey - also has tolerance and partial resistance to AYPR strain

What should be avoided to prevent the spread of rhizomania?

Soil and trash movement

How can damping-off in sugar beet be minimised?

A fine seedbed with good seed-to-soil contact, proper pH, adequate nutrition, and overall healthy crop conditions all help reduce damping-off.

Which seed treatment is standard for sugar beet to protect against damping-off?

All sugar beet seed is treated with Tachigaren (hymexazol) to help resist early fungal attacks.

What is damping off (black leg) in sugar beet?

Soil borne fungal disease that can kill seedlings pre and post emergence

What are the visual signs of downy mildew in sugar beet?

Distorted growth, yellowing on the leaf’s topside, and fungal sporulation on the underside.

When are conditions most favourable for downy mildew infections in sugar beet and how does it spread?

It prefers cool, wet and humid conditions around 10 to 12°C in the early part of the season, spreading via windblown spores.

What should be controlled in sugar beet to prevent the spread of beet rust, downy and powdery mildew?

Green bridge (volunteers, weed beet etc) should be removed/controlled to prevent the survival of downy mildew overwinter

Are any fungicides available for downy mildew control in sugar beet?

No labeled foliar fungicides currently exist; resistance varies among varieties, but no formal ratings are published.

Which mildew disease is most damaging and common in sugar beet?

Powdery mildew (host specific to SBE)

How does powdery mildew spread?

Via windblown spores

What does powdery mildew look like on sugar beet leaves?

Dusty white mycelium on the upper leaf surface which leads to chlorosis, reducing photosynthetic area

Which conditions encourage powdery mildew in sugar beet and in which location does the disease usually start?

It thrives in warm, humid environments around 20 degrees without free water on the leaves, commonly starting in warmer regions (essex) and spreading north.

How does powdery mildew affect sugar beet yield and sugar content?

It can cut yield up to 20% in severe outbreaks and also reduce sugar content.

Is there varietal resistance available to powdery mildew in sugar beet?

Yes - avoid growing susceptible varieties in locations with favourable weather conditions for the disease (essex)

Which fungicides can control powdery mildew, cercospora and ramularia in sugar beet?

• Revystar XE (fluxapyroxad + mefentrifluconazole) - max 2 applications per crop

• Caligula (fluopyram + prothioconazole) - 1 application after 1st September only on ware crops and not for feed

What does beet rust look like on sugar beet foliage?

It forms raised orange pustules (spore-producing structures) on both sides of the leaf, typically appearing later in summer in humid conditions after powdery mildew pressures.

Why are yield losses from beet rust usually lower than those from powdery mildew?

Rust tends to infect later in the season, so while it can cause some defoliation, its late arrival generally means smaller yield impacts (2-5% but up to 10% in worst cases)

Which products manage both powdery mildew and beet rust in sugar beet?

Revystar XE (fluxapyroxad + mefentrifluconazole) - max 2 applications per crop

How do Cercospora leaf spots appear on sugar beet?

They show up as grey necrotic lesions with black speckled centres and a brown outer ring - spots can coalesce

Which conditions are ideal for Cercospora development in sugar beet?

Warm temperatures of 23 to 27 degrees with intermittent rain

How does cercospora leaf spot spread in sugar beet?

It is blown in via the wind and spreads within the crop by rain splash

Why is controlling more than 5% leaf area infection by Cercospora important?

Exceeding this threshold typically causes economic yield losses, so timely sprays are key to limiting damage.

Where does the Cercospora pathogen survive through the rotation?

It persists mainly on infected crop debris in the field, allowing inoculum to carry over (green bridge should be controlled) - can also be seed borne

What increases the risk of cerspospora infection in sugar beet due to its survival on crop debris?

Short rotations and shallow cultivations

How does cercospora spread in sugar beet?

It is blown in via the wind and spreads within the crop by rain splash

Is there varietal resistance available to cercospora in sugar beet?

Yes (Magpie) - avoid growing susceptible varieties

Do fungicides cure existing Cercospora infections in sugar beet?

They only protect healthy tissue from new infections, should be applied at first sign of symptoms and repeatedly sprayed again within four weeks to maintain coverage.

What is the criteria for the risk forecast of cercospora to be triggered by BBRO ?

Two consecutive days with humidity above 90% and temperature greater than 25 degrees

Which fungicides are available for cercospora, ramularia and powdery mildew control in sugar beet?

• Revystar XE (fluxapyroxad + mefentrifluconazole) - max 2 applications per crop

• Caligula (fluopyram + prothioconazole) - 1 application after 1st September only on ware crops and not for feed

What differentiates Ramularia lesions from Cercospora lesions in sugar beet?

Ramularia has grey spore-producing bodies in the white lesion centre, whereas Cercospora shows black speckles in the centre and a distinct brown necrotic ring.

When would ramularia typically appear in a sugar beet crop?

Late in the season humid conditions with temperatures around 17 degrees

How significant is yield loss from ramularia in sugar beet?

It is typically less damaging than cercospora

How does ramularia spread in sugar beet?

It is blown in via the wind and spreads within the crop by rain splash

What is stemphylium in sugar beet and how severe can it be?

Uncommon disease in the UK, previously seen in Norfolk, with cases in the Netherlands causing up to 42% yield loss

What are the symptoms of stemphylium in sugar beet?

Small irregular yellow spots which die from the centre resulting in brown spots to form

Which conditions does stemphylium favour in sugar beet?

Wet weather and crop stress

Are there official label claims for controlling stemphylium in sugar beet?

No claims currently exist although an azole-strobilurin mix has shown to be effective

What are the symptoms of alternaria in sugar beet and when is the disease introduced?

It arrives at the end of the season, causing lesions to form with concentric ring patterns within them

What are the symptoms of phoma in sugar beet?

Large cream-coloured spots with concentric rings and black spots within the lesions

What should be done if root rot is detected pre-harvest in a sugar beet crop?

Infected fields should be harvested promptly and the beet should not be stored to prevent the infection spreading within the clamp (storage pile)

How does violet root rot survive in the soil?

As microsclerotia

Which soil conditions does violet root rot thrive in?

Warm and light soils around 20 degrees

What can increase the risk of violet root rot?

Close rotations of host crops which include all types of beet and potatoes

Which weeds can host violet root rot?

Potatoes, sow thistles, shepherds purse, annual nettles and chickweed

Why may violet root rot go undetected in sugar beet?

Symptoms may be subtle until lifting where diseased roots show purple discolourations - stunted patches may be seen pre-harvest if disease pressure is high

Why do stressed sugar beet plants on light sandy soils have a higher risk of fusarium infection?

Overall crop health can be lower due to soil conditions (lack of nutrition and structure, drought etc), allowing fusarium to infect causing the roots to go soft and spongy - brown dry rot

What can encourage fusarium infection in sugar beet?

Damage to the crown or roots, especially on light sandy soils when the crop is stressed

What is true for diseases such as powdery mildew, ramularia and alternaria in sugar beet?

They are host specific (different species to those found in other crops)