The main diseases which attack beans are:
- Botrytis (Chocolate Spot)
- Ascochyta (Leaf and Pod Spot)
- Downy Mildew
Botrytis (Chocolate Spot)
Beans are attacked every year by chocolate spot, so all crops need protecting. The date of sowing, location and weather are the main factors determining the severity of the attack. Early sown autumn crops are more susceptible than late sown crops. Warm, wet weather favours the disease, and a heavy attack can defoliate a crop within 2 weeks. Crops in coastal areas are more susceptible than those located inland.
All crops should be inspected during flowering (i.e., during May for autumn sown crops and during June for spring sown crops) and sprayed if the level of chocolate spot is building up. Apply a second spray at the end of flowering or before the crop gets too tall to take a sprayer.
Ascocyhta (Leaf and Pod Spot)
This disease is mainly found on autumn sown beans. Spring sown crops rarely suffer yield losses from Aschohyta. The main source of Ascochyta is infected seed. Infection can also spread from over wintering bean volunteers in nearby fields. There is no effective foliar fungicide available to control this disease, so prevention is the only answer. Use disease free seed and resistant varieties. Destroy all bean volunteers on the farm before drilling the new crop.
Occasionally, both winter and spring bean crops are attacked by downy mildew, which can spread rapidly during warm weather. It rarely causes serious damage, but if the disease is spreading during late May and June, a preventative spray may be worthwhile. Folio Gold is the main spray used.
Rust can attack beans, but it is very rare in Ireland.
Sclerotinia is a soil borne disease and is prevented by good rotation.
A 2-spray program is suggested for beans, with Chocolate Spot the main threat.
Control Chocolate Spot at the first signs of infection (usually at start of flowering or earlier in coastal areas).
Options include: Signum 0.5 kg/ha
Amistar 0.5 l/ha + Folicur/Fezan etc 0.75 l/ha
Repeat 2-3 weeks later. These products also offer control of Ascochya.
Treat Downy Mildew (if seen or high risk) at start of flowering.
Earlier treatment was not beneficial in NIAB trials but early infection should be monitored.
Dithane offers protective control mainly while Metalaxyl M (in Ridomil Gold) offers some curative control. Ridomil Gold and Dithane have off-label clearance for use on beans.
Bean rust is usually not problematic and will be well controlled by Folicur/Fezan etc, Amistar or Signum.
Products that are cleared for use on peas and beans are available at: