PGRO advises pulse growers on common diseases to watch out for

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The Processors and Growers Research Organisation (PGRO) has updated pulse growers on the common diseases in peas and beans, their symptoms, risk factors for disease development and management options.

The new advice is featured across two new videos released as part of its ‘Masterclass’ series.

Lea Herold, plant pathologist, is advising growers to get informed about the symptoms of common diseases in peas and beans before they occur including foot rot, downy mildew, powdery mildew, chocolate spot, and sclerotinia.

In addition, Dr Herold suggests the most effective treatments to tackle these diseases and prevent their knock-on effects on yield.

Foot rot

The potentially most damaging disease for peas and beans is foot rot, a soil-borne disease that is caused by a pathogen complex which infects roots and compromises water and nutrient uptake.

“Early symptoms of infection include an upwards yellowing of foliage followed by wilting in peas and blackened stem bases and roots in beans,” explains Lea. “Severe infections can stunt plants and even lead to plant death. Potential yield losses are high and complete crop losses can occur in heavily infected fields.

“The risk of disease development is greatest on heavy soils, in fields with poor soil structure and in close rotations. Compaction and water logging greatly increase risk, plus anything else that causes stress in plants. Weak seedlings and crops sown into cold soils are also more prone to disease establishment. The healthier the soil, the lower the risk and using cover crops in pea rotations can play a huge role in minimising the risk of disease.

“Since foot rot is soil-borne, using fields without or low pathogen presence is an important management tool. We offer a soil test for pea crops that determines levels of pathogens in soils and gives an associated risk of infection for each of the pathogens and an overall risk for the field. Using this test will help growers to avoid fields with a high risk of disease development and associated yield losses. We recommend to sample fields in the autumn, prior to planting, at the latest and to sample a minimum of 25 random locations per field to a depth of 20 cm.”

Downy mildew

Primary infection of downy mildew is caused by soil-borne spores, and infected pea plants are stunted and covered in grey mycelium. Disease spread begins in primary infected seedlings providing the source for secondary infection by air borne spores while secondary infection is characterised by lesions covered in grey mycelium on the underside of pea leaves.

Dr Herold says: “Early sown crops, especially close to the coast, in cold soils with a field history of downy mildew are at greatest risk.

“The descriptive lists for combining peas and vining peas include tolerance ratings for downy mildew. Varieties with a rating of 7 or higher are best suited for higher risk areas. Currently, we can still use the seed treatment Wakil XL on crops sown between the 1st of April and the 29th of September.

“However, it is very likely that use of seed treatments containing metalaxyl-M will be restricted to indoor use only from the 1st of June this year. This means that we will not have any fungicidal seed treatment available to peas for next season.”

“In vining peas, Revus (active substance mandipropamid) is approved for downy mildew control but no foliar fungicides are approved for downy mildew control in combining peas.

“In beans, downy mildew is characterised by pale lesions on the upper side of the leaves, which are covered in grey mycelium on the underside of the leaves, and spring beans are more likely to be impacted by downy mildew than winter beans. Symptoms usually appear from early May in periods of cooler and wet weather and severe infection can result in up to 30% yield reduction.

“The descriptive lists for spring beans include tolerance ratings for downy mildew. Varieties with a rating of 7 or higher are best suited for higher risk areas. Currently, metalaxyl-M is approved for downy mildew control in beans and a spraying threshold of disease presence on 25% of plants is advised.

Botrytis and sclerotinia

Botrytis and Sclerotinia are diseases in peas whose development is strongly weather dependent and, in the case of Sclerotinia, also on whether other host crops are grown in the same rotation, Dr Herold says.

“If the weather is wet during petal fall, there is a disease risk present. Approved fungicides are protective only and we recommend spraying at first pod if wet weather is forecast. Several active ingredients are approved for control and can be found in the PGRO Agronomy App and Vining Pea Technical Updates.”

Powdery mildew

“Powdery mildew is a late season disease in peas and infected plants are covered in white mycelium which impairs photosynthetic activity and also affects operator health and machinery in vining peas.

“The risk for disease development is greatest in late sown crops from July onwards in periods of warm days and humid nights. Varietal differences for powdery mildew susceptibility can be found in the descriptive lists. Although Sulphur (Thiopron under an EAMU) provides some control, it is preventative only.

Chocolate spot

One of the most damaging diseases in beans is chocolate spot, usually occurring from May onwards, and winter beans are more prone to disease development than spring beans, Lea cautions.

“The name comes from the chocolate coloured, small, round lesions appearing on leaves which can, if left uncontrolled, merge, and necrotic areas can then cover large areas of the leaves. Yield impacts of up to 50% have been seen.

“The risk for disease development is greatest in early sown winter beans with high plant density – the associated microclimate is very conducive for chocolate spot development. Beans grown in the west and north of the country are also at greater risk.

“Control is essential if cool and wet weather is forecast during flowering. The best spray timing to protect yield is at mid flower (first pod) and several actives such as azoxystrobin and boscalid plus pyraclostrobin provide control of chocolate spot.”

Bean rust

Bean rust is a very damaging late season disease, with infection beginning in periods of warm days and humid nights, usually from June to July onwards.

Lea clarifies: “Rust coloured pustules occur on leaves which can, if left uncontrolled, cover the whole leaf area quickly which then leads to defoliation of crops. In fact, yield reductions of up to 70% are possible.

“The risk for disease development is greatest in warm summers and control is essential if disease develops before pods are filled. The best actives for rust control are azoxystrobin and tebuconazole and these should be applied at late flower.”

You can hear more advice on common pea and bean diseases from the PGRO’s Dr Lea Herold in the latest Masterclass video now available on YouTube.


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