Cool and wet conditions through March have increased the risk of chocolate spot on established beans this season, as well as the threat from downy mildew on new leaf growth and for later emerging spring beans.

Many autumn sown bean crops have been hit hard by harsh winter frosts. Below average temperatures and heavy rain through March had also stopped early spring recovery and increased disease risk, warned Syngenta Technical Manager, Simon Jackson.

“That has been exacerbated where rain splash has spread chocolate spot spores from existing lesions on lower leaves, onto new growth. PGRO disease reports have highlighted high levels of chocolate spot in some crops, along with cercospora.

“The sequence of Amistar and Elatus Era has proven to be highly effective as a fungicide strategy for both chocolate spot and rust control in beans. The decision for growers and agronomists this season, will be to assess in which order to apply them,” Simon advised.

“Where chocolate spot is already present in the crop and conditions continue encourage the disease, it would be advisable to start the programme with an Amistar application from first flowering (GS60),” he advocated. The strategy will be particularly beneficial as temperatures start to warm up and soil moisture levels are not limiting growth.

Field assessments indicate crops that are looking particularly stressed and struggling could well benefit from supplementary trace elements, suggested Simon, principally manganese and magnesium, along with zinc. Results of last year’s ADAS YEN bean crops showed that, although there was no direct correlation, the better performing crops had received foliar trace elements.    

With rapid compensatory growth in warmer conditions, crops are expected to quickly build big canopies, reported Simon. However, that will tend to make them more susceptible to chocolate spot as the season progresses. “The key timing for Elatus Era application is likely to be around early to mid-May for optimum disease control.” That leaves the option for a final Amistar + tebuconazole treatment towards the end of May or early June, to further protect from rust infection through to the end of the growing season. 

Slow progress for spring bean crops so far this season will focus agronomy on providing adequate nutrition to increase plant stand and prolong growth for as long as possible, along with disease control for green leaf retention to boost yields, advised Simon.

“Depending on disease pressure, most spring crops still benefit from a two-spray foliar disease programme. That is likely to be an Amistar treatment in early June, followed by Elatus Era in early July when the crops have built a full canopy,” he added.    

PGRO has also reported that weather conditions experienced this season could also result in increased downy mildew infections. The disease is typically an issue on emerging spring beans, but has also been widely identified on the new growth of winter beans in similar high-risk spring conditions. An EAMU (20130917) is available for the fungicide SL567A, containing the highly systemic metalaxyl-M, to control downy mildew infection on emerging leaves in field bean crops.