Key bean fungicide timing set for earlier window this season

The key bean fungicide timing at the first pod set stage could happen as early as the end of April, according to current crop growth indications.

With many bean crops already threatened by the high-pressure wave of chocolate spot which swept through crops earlier this season, keeping newly emerged leaves green will be important.

In worst-case scenarios, chocolate spot has decimated some fields. Fortunately, crops that received an early fungicide treatment have recovered, with clean growth now emerging.

See also: Why pollinators are key to Scottish grower’s 6t/ha bean yield

However, significant levels of inoculum are still present on lower diseased leaves, meaning growers will need to keep on top of the disease.

Syngenta technical manager Simon Jackson notes that keeping new leaves as green as possible is particularly important as crops reach the all-important first pod stage.

“Current crop growth would indicate the first pod stage will be earlier than normal. Treatment timings are a balance between managing costs and necessary disease control,” he says.

Simon Jackson © Syngenta

The first key bean fungicide timings, as shown by research at PGRO, is the first pod set. The final application is made 21-28 days later.   

Fungicide applications from first flower buds visible (BBCH51), could potentially happen as early as late April this season, says Simon.

Mid-April is also a good time to think about nutrition in beans, highlighting the importance of healthy nutritionally balanced crops in combating disease. 

Beans respond especially well to sulphur supplements, which should be considered at the April timing along with magnesium.

Trace elements such as manganese, boron and zinc should also be assessed, with leaf tissue analysis giving an indication of crop nutrient status. 

Fungicide products

Given the disease risk this year, Simon recommends a robust rate of 0.66 litres/ha of Elatus Era (benzovindiflupyr and prothioconazole) for control of chocolate spot and rust, followed by Amistar (azoxystrobin) 21 to 28 days later to provide good control of rust later in the crop.

“This will give broad spectrum protectant disease control with a good contribution to downy mildew which may appear late,” he advises.

“We would recommend mixing Amistar with a triazole if rust pressure is high, or there is still chocolate spot is still present.

“The aim to help make bean yields more consistent, resulting in a more sustainable return from this important crop,” he adds.

Bacteria boost

Recent trials work with PGRO has shown that a unique bacteria solution which fixes atmospheric nitrogen, known as Vixeran, helps improve bean yields, with crops retaining more pods per plant with improved bean weight.

Bean plants are naturally set up to work with symbiotic rhizobium bacteria found in their root nodules.

“The Vixeran lives in the leaves and around the root to fix further atmospheric nitrogen into ammonium, which is readily available to the plant,” explains Simon. 

“This can be especially beneficial where soils are inherently low in rhizobial bacteria, or where the nodules have been damaged by pea and bean weevil larvae.”

He recommends a Vixeran application from the six-true leaf stage (BBCH16), through to early flower.

“Application conditions are more crucial than timing,” says Simon. “The crops should be actively growing. Avoid application just before or after frost events and aim to avoid treatment if periods of bright sunshine are forecast immediately after application.”