Pea and bean growers are being warned that downy mildew is highly prevalent in crops this season and treatments may be needed to minimise yield losses.
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 disease is even hitting winter bean plants at levels that would warrant treatment, according to the Processors and Growers Research Organisation (PGRO).
Infection has been triggered by recent weather – exacerbated by cool, overcast conditions and recent rains. High humidity and low seasonal temperatures could now encourage outbreaks of secondary infection on leaves, with more serious yield effects.
Winter and spring
PGRO research and development manager Becky Howard reported: “Although it is generally spring beans that suffer more damage from downy mildew, winter beans have been displaying high levels of infection that may warrant treatment.
“Where plants are already showing signs of infection, growers should be looking to prevent spread onto new growth,” she advised.
An extension of authorisation for minor use is available for the fungicide SL 567A, containing the highly systemic metalaxyl-M to control infection in emerging leaves.
PGRO also warns downy mildew is creating a threat to establishing pea crops.
For vining pea crops, Revus (mandipropamid) is approved for control of the disease. However, no foliar fungicides are available for use in combining peas.
Syngenta technical manager Andy Cunningham pointed out that continued cool, wet conditions would also be conducive to chocolate spot developing in beans as the season progresses.
“If the weather turns hotter and drier, that would be good to reduce pressure from downy mildew and chocolate spot,” he advised.
“However, it would mean that rust is more likely to occur, with early infections the most damaging in terms of yield effects.”
This season, bean growers have the new option to use Elatus Era (benzovindiflupyr + prothioconazole) in beans, which has proven highly effective in the programme to control both chocolate spot and rust – whatever the weather conditions.