Pea Aphids On Peas, Fababeans And Lentils
Host Crops
Field peas, alfalfa and clovers are the main hosts of the pea aphid (Acrythosiphon pisum). Other legumes, including lentils, fababeans, vetches, sweet clover, sweet peas, trefoil and dry beans are also hosts.
The pea aphid was introduced to North America from Europe, first reported in Illinois in 1878, and near the turn of the century they were found near Ottawa, Ontario.
Biology
Adult pea aphids are soft-bodied, slow-moving, and range in colour from light to dark green. Although less common there is also a red colour morph. They are pear shaped, about 3 mm (1/8 in.) long and 1.5 mm (1/16 in.) wide, with long slim legs. The antennae of the pea aphid show narrow dark bands at the tip of each segment. The nymphs are smaller but closely resemble the adults.
Pea aphids overwinter as eggs on leaves and stems of perennial legumes (ex, on the crowns of clover or alfalfa). In the spring, when plants resume growth, a small, light green, wingless female hatches from each egg. These aphids, which are all females and are called "stem mothers", can reproduce without mating. They feed on the growing plants and give birth to female young. Some aphids of the second and third generations become winged and migrate to field peas and other acceptable host plants. There they feed and produce wingless females that give rise to winged and wingless females.
Aphids develop from birth to maturity in 5 to 50 days depending on the weather. The optimum temperatures for rapid development of pea aphids range from about 23 - 28ºC. All pea aphids are female throughout spring and summer. A summer female can produce 50-150 young during her life. If the host crop is cut during spring or summer, the winged aphids leave to search for new plants on which to live.
In late September or October, winged males and wingless females are produced. These mate and the females lay eggs on leaves and stems. There may be seven to 15 generations per year.
| May | June | July | August | September |
| Overwintering eggs hatch | Feeding by nymphs begins, new adults emerge | New adults disperse and lay eggs, nymphs feed | New adults disperse and lay eggs, nymphs feed | Adults disperse, lay eggs that overwinter |
Scouting For Aphids In Field Peas
Field Peas should be checked for aphid levels at the beginning of flowering. Take 180° sweeps or check at least 5, 8-inch (20 cm) plant tips along four well-spaced stops in the field.
Counts should be at least 50 m (150 ft.) apart and observations should be made well into the centre of the field. The number of aphids per sweep and aphids per tip in field peas are related. Either technique can be used to determine if the economic threshold has been exceeded.
Economic Thresholds For Aphids In Field Peas
Sampling to determine aphid density should be done when 50 to 75% of the pea plants are in flower. Economic thresholds may vary depending on the value of the crop and cost of control, as well as variation in potential seed weight caused by variation in precipitation and heat stress. The economic threshold in peas at $0.21/kg ($5.71 per bushel) and average control cost of $16.63-$22.86/ha ($6.73-$9.25/acre) is 2 to 3 aphids per 8-inch (20 cm) plant tip, or 9 to 12 aphids per sweep, at flowering. If the economic threshold is exceeded, a single application of insecticide when 50% of plants have produced some young pods will protect the crop against yield loss and be cost-effective. Cultivars of peas may also vary in their tolerance to feeding by pea aphids, thus economic injury levels may differ between cultivars. The economic thresholds presented above were developed using “Century” field peas.
Research in Manitoba has shown that insecticides applied when pods first form protects pea yield better than earlier or later applications. Control at the early pod stage provides protection through the pod formation and elongation stages, which are very sensitive to aphid damage.
Aphid feeding on peas in the flowering and early pod stage can result in lower yields due to less seed formation and smaller seed size. Protein content and other quality issues do not appear to be affected.
The following table relates the yield loss in peas for average aphid counts per sweep or per 20-cm tip of a field pea stem when about 25 percent of the crop has begun to flower.
| Aphids per sweep | Aphids per tip | % yield loss |
| 7 | 1 | 3.4 |
| 10 | 2 | 4.9 |
| 12 | 3 | 6.1 |
| 15 | 4 | 7.1 |
| 16 | 5 | 8.0 |
| 18 | 6 | 8.8 |
| 20 | 7 | 9.6 |
| 21 | 8 | 10.3 |
Economic Threshold For Aphids In Lentils
For pea aphids in lentils, a nominal threshold is 30 to 40 aphids per 180° sweep of a 38 cm (15 inch) diameter insect net, and few natural enemies are present, and when aphid numbers do not decline over a 2-day period.
Management Tips
Seeding early in the spring may reduce yield loss due to pea aphids in some cultivars of peas.
Biological Control: Some biological control of aphids occurs by predators such as lady beetles, larvae of syrphid flies, minute pirate bugs and damsel bugs. At least five species from a family of parasitic wasps known as Aphidiidae are known to attack pea aphids in Manitoba. The most common of these is a species known as Aphidius ervi. A fungal disease may sometimes reduce levels of pea aphids in warm, moist weather.
Insecticides:
| Insecticides for control of aphids in field peas, faba beans and lentils in Canada | |||
| Insecticide | Crops | Rate/Acre | Pre-harvest interval (days) |
| Beleaf | Faba beans | 49-65 g | 7 |
| Movento | Field peas, lentils | 75 - 111 ml | 7 |
| Sivanto Prime | Field peas, faba beans, lentils | 202-304 ml | 7 |
| Matador/ Silencer/ Labamba | Field peas, faba beans, lentils | 34 - 94 ml | 14 (Matador/ Labamba); 21 (Silencer) |
| Voliam Xpress | Field peas, faba beans, lentils | 91-223 ml | 14 |
| Malathion | Field peas | 445 ml | 3 |
| Lagon/Cygon | Field peas | 110 - 150 ml | 3 - 21 |
Revised: July 2022
For further information, contact John Gavloski, Entomologist, Manitoba Agriculture, Carman, Manitoba, Canada, 204-750-0594.
