Faba Beans

Ascochyta blight is a seed-borne or residue-borne disease of faba beans in Western Canada. Ascochyta leaf and pod spot is caused by Ascochyta fabae. It is not the same Ascochyta species which infects other pulses and is specific to faba beans.

Leaves, stems, pods, and seeds can all be infected. Lesions appear as tan or grey spots with dark margins, and tiny black fruiting bodies (pycnidia) in the centre. Cool, rainy weather is conducive to the spread and infection of the disease and is most damaging to maturing pods and seeds if prolonged wet weather occurs during July and August. In severe infections, seeds developing in the pods become discoloured and shrivelled. Severely infected seed lots may not be marketable or will be downgraded severely due to discolouration.

Producers are advised to have their seed tested for seed-borne Ascochyta blight at an accredited seed test laboratory. Ascochyta blight inoculum also overwinters on faba bean residue, so producers should not plant faba bean on faba bean stubble.

If disease inoculum is present and weather conditions favour disease development, a fungicide should be applied to protect healthy plant material. Apply fungicide at the beginning of flowering or the onset of symptoms. Usually, one well-timed application is sufficient for controlling faba bean diseases.

Avoid consecutive sprays of the same fungicide group to avoid the development of fungicide resistance.

Anthracnose in faba beans is caused by Colletotrichum truncatum. This is the same species which causes Anthracnose in lentils and field peas.

Crop rotation is the key to preventing this disease as it allows time for faba bean residue to decompose and break the disease cycle. Allow three to four years between faba bean crops. Also, avoid growing faba beans after lentils or peas. Faba beans should not be planted adjacent to the previous year’s faba bean, lentil, or pea fields to reduce the spread of residue and wind-borne spores.

Plant seed that has zero or acceptable levels of seed-borne disease, as determined by an accredited lab. Use seed treatments to protect the seed and seedlings from seed-borne diseases.

Chocolate spot is caused by Botrytis fabae and Botrytis cinerea and can be residue-borne or seed-borne. Botrytis cinerea is the same species which infects lentils, causing grey mould on the stem and pod rot. Botrytis chocolate spot is a major disease of faba bean in other parts of the world. This disease often sets in later in the season with minimal impact on yields, however, early infections can result in yield loss.

First, small reddish dots appear which grow into well-defined blotches with reddish-brown margins and tan centres on the leaves, stems, and pods. If conditions are suitable, the lesions grow and merge, resulting in blackening and partial defoliation.

Avoid growing faba beans after lentils in areas where this disease is present. Follow a crop rotation of four years between successive crops of faba beans and avoid buckwheat or lentils in the rotation. However, Botrytis spp. can survive in the absence of a host crop, so crop rotations will not eliminate the disease. It is also important to use disease-free seed. Fungicides should be applied at early flower or before the onset of symptoms.

Sclerotinia stem rot is common in many broadleaf crops in Western Canada, but so far is less of a problem with faba beans. This disease may appear late in the season with minimal impact to yield.

Crop rotation is the key to preventing disease. Sclerotinia sclerotiorum will affect other host crops in the rotation so allow three to four years between faba beans and other host crops. Faba beans should follow a cereal crop in the rotation, rather than an oilseed or pulse crop. Research-based on soybeans found that no-till may result in fewer white mould fruiting bodies as compared to minimum tillage.

Apply fungicides at early flower followed by a second application seven to 14 days later if the disease persists, or if weather conditions are favourable for disease development. Use higher registered rates (if applicable) to obtain extended protection and maximum yield benefit. Follow label directions specific to the product used.

Note that it is too late to control Sclerotinia white mould once symptoms are observed, so forecast to determine the risk of disease development.

Rust is caused by Uromyces fabae. Rust can be a highly destructive disease of faba bean in other countries but has rarely caused losses in Canada. The disease relies on high humidity and is spread by late-season irrigation.

Rust-coloured, blister-like pustules develop on the leaves and stems surrounded by chlorotic halos. Spores can survive on crop residue and seed so a crop rotation of at least two years between faba bean crops should be used. Currently, no products are registered for control.

This disease can be found in faba beans. Other pulse crops are susceptible to this virus, therefore, avoid planting faba beans near established fields of forage legumes.

Aster yellows is a common disease on faba beans in Western Canada, however, usually only one to 2% of the plants are infected and economic losses do not occur.

Initially, there is yellowing of the area between leaf veins. This is followed by progressive leaf death and dieback starting at the leaf margins. Additional symptoms include loss of lower leaves, stunting, and failure to flower. When infection occurs early in the season, the upper pods formed after the infection are small and do not set seed, while the lower stem is normal. Most infected plants die within several weeks after the onset of the first symptoms.

The disease is transmitted by an insect vector – potato leafhoppers. Leafhoppers arrive on winds from the southern United States as early as March. Although there are local leafhopper populations, infected leafhoppers from the United States are thought to be the primary source of infection. If economic thresholds are met, the disease can be controlled by controlling the leafhoppers.

Alternaria leaf spot is caused by Alternaria alternata, and Powdery mildew is caused by Microsphaera penicillata var. ludens. Fungicides are registered for the control of powdery mildew on faba beans.

Lygus bugs can cause quality loss in faba beans, as they will move into the crop after other crops have matured and feed by using their sucking mouth parts to make pin holes in the seed coat.

Lygus bug infestations have posed a significant threat to profitable faba bean production in Alberta, due to the extensive acres of canola. As canola is harvested first, the lygus bugs move into the still green faba bean fields and damage seeds in the developing pods. Human consumption of faba beans has a very low tolerance for lygus bug damage (less than 1% for Grade No.1).

Three species of caragana or blister beetle will attack faba beans. Blister beetles often attack faba beans in swarms, but generally in small patches within the field. They usually do not feed for very long before moving elsewhere. Therefore, control measures are difficult to employ and there are no established action thresholds for faba beans.

(Potato leafhoppers) are the vector insect for aster yellows of faba beans but are also a sucking insect. Aster yellows are rarely yield-limiting in faba beans. Faba bean damage from leafhoppers can consist of distorted growth and plant stunting. Populations mainly blow in from the southern United States, but there are also small native overwintering populations.

The pea aphid adult is small, about 4 millimetres (0.15 inches) long, light green, and long-legged. The insect may be wingless or have prominent, translucent wings. Although pea aphids rarely survive winter in Saskatchewan, they may overwinter as an egg attached to the stems or leaves of alfalfa or clover. The eggs hatch in early spring and the young aphids feed on the newly emerged alfalfa or clover plants. During May and June, a new generation develops wings and with the aid of wind currents, flies to faba bean fields. Most aphids in faba bean fields are blown in on warm southerly winds from the United States in June or early July. The pea aphid weakens the plant by sucking its sap and is responsible for transmitting viral diseases.

Pea leaf weevil (Sitona lineatus) is a new and major threat in peas and faba beans. The main concern is larvae feeding on the nitrogen-fixing nodules. Feeding results in characteristic leaf notches but fortunately pea and faba bean seedlings can tolerate leaf notching and will usually recover unless there is very heavy feeding pressure.

The proportion of seedlings with terminal leaf damage (ex. leaf notches) provides an adequate indication of overall plant damage, and to some extent, potential yield losses. It is therefore recommended to inspect the average feeding damage on the terminal first leaf in 10 seedlings, five along the perimeter of the field, and five within the field. The action threshold for control is 30% damaged seedlings.

In the spring pea leaf weevil adults fly to legume fields where females lay eggs near the base of the host plant. The larvae feed on Rhizobium nodules. At maturity, larvae pupate in the soil and adults emerge to feed on leaves until late summer. Adults overwinter in field margins or alfalfa. Fortunately, there is no evidence of Sitona lineatus overwintering in stored grain. Pea leaf weevils are spreading outwards from the southwest corner of Saskatchewan and are a pest to watch for.

Where yield loss occurs, is primarily a result of the larvae feeding on the Rhizobium nodules reducing nitrogen to the crop. Seed treatments are the only available control for larvae feeding in faba beans. Control products currently registered for pea leaf weevil control in faba beans include seed treatments from the insecticidal group neonicotinoids.

Cutworms and wireworms can attack a wide variety of crop species and may attack faba beans. However, faba beans are very resilient, as they have growing points near the seed that enables the plant to regrow following below-ground insect feeding on the emerged or emerging seedling. Under high-risk situations, or where insect pressure is severe, there are insecticides registered for use in faba beans.