FP Insects

Scouting for Pea Aphids

Identification

Pea aphids are a sporadic pest of field peas, faba beans and lentils in Manitoba that overwinter in perennial legumes. Once hatched, adults may fly to neighbouring pea crops. Pea aphids tend to feed on the newest leaf tissue and most sensitive, yield-producing parts of the plant. They can cause yield loss by feeding on peas during the pod formation and elongation stages, reducing seed formation and seed size.

Adult pea aphids are about 3 mm (1/8 inch) long and 1.5 mm (1/16 inch) wide. They are soft-bodied, pear shaped insects with long slim legs and antennae that have narrow dark bands at the tip of each segment. Pea aphids range in colour from light to dark green and may be winged or wingless. Nymphs of pea aphids are smaller but look very similar to adults.

Scouting Tips

  • Begin scouting toward the end of June to early July, when 50-75% of the crop is in early flower.
  • Check five plant tips (top 8 inches) or conduct 10 sweeps using a sweep net, at four locations (>50m apart) in each field. If you are inspecting plant tips, unfold the clam leaf (newest stipule) to check inside for aphids.
  • Assess populations in various locations of the field, including field edges. Pea aphid populations may be higher near field edges.

Threshold and Control

The threshold in field peas is 2-3 aphids/plant tip or 90-120 aphids/10 sweeps (or 9-12 aphids per single sweep). Note that this economic threshold was developed in Manitoba using Century peas, an older pea variety. Natural enemies including lady beetles and larvae, hoverfly larvae, minute pirate bugs, damsel bugs, parasitic wasps and fungal diseases will also keep pea aphids populations in check. If the threshold is reached, apply a registered foliar insecticide at early pod (when 50% of plants have produced young pods).

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 during the flowering and early pod stages 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.

Table 1. Yield loss in peas for average aphid counts per sweep or per 20-cm plant tip when approximately 25% of the field has began flowering.
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

Research on pea aphids in lentils and faba beans is on-going at the U of S/AAFC. Preliminary results on faba beans have shown no significant difference in yield between applying insecticide at 50 aphids/plant and 120 aphids/plant. In 2019, faba beans with a population of up to 800 aphids/plant prior to insecticide application experienced 50% yield loss. Complete yield loss occurred at 1500 aphids/plant. It was also determined that a population of 280 aphids/plant can increase to 800 aphids/plant in less than a week.

Preliminary results show that lentil crops also benefit from insecticidal control at lower aphid populations. In 2019, lentil yields were reduced to ~2 tonnes/ha from 1000 aphids/sweep. The current nominal threshold for pea aphids in lentils is 30-40 aphids per 180° sweep of a 38 cm (15 inch) diameter sweep net, with a few natural enemies present and with aphid numbers remaining high over a two-day period.

Additional Resources

Pea aphids in peas, faba beans and lentils – Manitoba Agriculture and Resource Development web page
Controlling Pea Aphids in Lentils and Faba Beans – Pulse Beat Issue 90 article by Ningxing Zhou, Sean Prager (University of Saskatchewan) and Tyler Wist (Agriculture and Agri-Food Canada)