There are five insects considered to be pests of faba bean: grasshoppers, lygus bugs, blister beetle, aphids, and pea leaf weevil. Below is a description of these insect pests and control methods.
Grasshoppers can be a major pest of faba bean. There are more than 80 species of grasshoppers on the prairies but only three species threaten faba bean. These three pest grasshoppers generally favour faba bean foliage and will feed on faba bean even when other food sources are available.
The three species of grasshopper that threaten faba bean are: Melanoplus bivittatus (Twostriped grasshopper), Melanoplus packardii (Packard grasshopper), and Melanoplus sanguinipes (Migratory grasshopper). They are all spur-throated and have a spine below the head.
No economic thresholds have been established for faba bean. Usually grasshopper infestations of 10/m2 (1/ft2) do not cause economic losses in peas, and faba bean thresholds are thought to be lower than this. It is also important to note that the first adult grasshoppers appear on the prairies by late May but they are not typically pests.
If control is needed, the optimal timing is when nymphs are at the third instar stage, which is usually about mid-June. It is critical to apply only insecticides registered for use in faba bean and to respect the pre-harvest interval (PHI) of the insecticide selected to maintain crop marketability. All grasshoppers are susceptible to pyrethroids, certain organophosphate insecticides, and carbamate insecticides.
Lygus bugs can cause quality loss in faba bean, 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 faba bean has a very low tolerance for lygus bug damage (<1% for Grade No. 1).
Caragana or Blister Beetle
Three species of caragana or blister beetle will attack faba bean. Blister beetles often attack faba bean 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 bean.
(Potato leafhoppers) are the vector insect for aster yellows of faba bean, but are also a sucking insect. Faba bean damage 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. Matador® and Silencer® are registered for control of leafhoppers in faba bean.
Aphids (Pea Aphids)
The pea aphid adult is small, about 4 mm (0.15 in) 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, fly to faba bean fields. The majority of 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
Pea leaf weevil (Sitona lineatus) is a new and major threat in peas and faba bean. The main concern is larvae feeding on the nitrogen fixing nodules. Feeding results in characteristic leaf notches. 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 (i.e. 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 per cent damaged seedlings.
No control products are currently registered for pea leaf weevil control in faba bean. In pea, registered control products include: seed treatments from the insecticidal group neonicotinoids a.i. thiamethoxam (Cruiser 5FS®/ Cruiser 350FS®/ Cruiser Maxx Pulses®), and the insecticidal group pyrethroids a.i. lambda-cyhalothrin (Matador®).
In the spring pea leaf weevil adults fly to legume fields where females lay eggs near the base of host plant. 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 in alfalfa. Fortunately, there is no evidence of Sitona lineatus overwintering in stored grain.
Pea leaf weevils are spreading in southwestern Saskatchewan. The area is suitable for the establishment of this pest, however, establishment does not mean pest status, as the degree of damage varies from year to year. In Alberta, monitoring has shown that pea leaf weevils are not moving north of the Trans-Canada Highway. However, they are moving east. This may be due to failure to survive winter conditions in the north.
Cutworms and wireworms can attack a wide variety of crop species and may attack faba bean. Currently, no products are registered for control of these insects in faba bean and control measures are limited to cultural practices.