Rotation: broad beans can be a useful break crop between cereal crops, but only
once every five years, to avoid build-up of Stem Rot (Sclerotinia) (see “Diseases”,
below).
Pests:
penetrating the plant tissue, transmitting virus diseases and encouraging fungus
diseases. The aphids often congregate at the tops of stems, so with smaller plots of
beans these can be cut off and destroyed. Pyrethrum effectively controls aphids but
should only be sprayed at night to avoid killing bees, which habitually visit the bean
flowers.
The Pea Aphid and Vetch Aphid also transmit virus diseases.
- Pea and Bean Weevil—the soil coloured adults live in the soil in the day and feed
on the leaves at night, but it is the larvae which do the damage by feeding on the root
nodules. Deterred by applying lime or soot on the dew soaked plants, or by spraying
nicotine or quassia (a natural insecticide) on the plants and surrounding ground.
Diseases:
Chocolate Spot—the most serious disease, especially on young plants. Fungicides
such as Bravo, MBC, Ronilan and Rovral, are all mainly contact/protectant
chemicals and must be applied before the fungus gains entry to the leaf or stem.
Once a leaf is infected, spraying has little or no effect. Some control by removing all
the haulm from previous crops, deep ploughing and correcting any potassium
deficiency in the soil with appropriate fertilisers or wood ash. Spring sown crops
normally suffer less than autumn sown ones.
Downy Mildew seems to be increasing in significance. Mainly spread by wind-
borne spores. The youngest leaves of the plant are the first to be attacked. Apply a
foliar spray of metalaxyl plus chlorothalonil (Ridomil + Bravo) if the disease is
spreading in the crop during flowering. A repeat spray 10–14 days later may be
necessary if the disease pressure remains high. The disease occurs mainly in warm
damp sheltered sites.
Leaf Spot (Ascochyta)—mainly a problem of winter-sown beans , and worse in hot
and humid conditions, but rarely causes big yield loss. The disease is seed-borne so
it is controlled with clean or dressed seed. No effective fungicide available. Destroy
all volunteer beans in nearby fields before the new crop emerges. - Bean Mildew—spray with Bordeaux mixture.
- Root Rots—occur mainly in the tropics and subtropics. Control with seed dressing
eg Captan (NB Captan is very highly toxic to fish and most aquatic invertebrates).
crop two or three times with lime sulphur gives some control.
However in northern Europe rust normally appears at the end of the season and is
often welcomed as an aid to desiccating the crop prior to harvest.
- Stem Rot (Sclerotinia sclerotiorum)—although not common, beans may develop
this disease. Sclerotia develop in the soil, and produce spores that infect bean stems
(also linseed, oilseed rape and field peas). New sclerotia develop here and interfere
with the plants water conduits, so that all plant parts above the infection die of “thirst”. - Virus Diseases—Mosaic, Leaf Roll and others. Transmitted by aphids.
- Broad Bean Rust—a major problem in countries such as Peru and Egypt.
- Powdery Mildews—can be very damaging, in Sudan for example. Spraying the
- Black Bean Aphid (Blackfly) (Aphis fabae)—these can devastate crops, by