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 economic threshold for control is 2-3 aphids/plant tip or 90-120 aphids/10 sweeps (or 9-12 aphids per single sweep). If the threshold is reached, apply a registered foliar insecticide at early pod (when 50% of plants have produced young pods).

This economic threshold was based on $5.71/bu peas and an older pea variety, Century. While higher crop prices exist today compared to when this threshold was developed, current pea varieties are also expected to be able to tolerate more aphid feeding than Century peas. As a result, the threshold of 2-3 aphids/plant tip or 9-12 aphids/sweep is maintained.

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. Look for these natural enemies while scouting for pea aphids and consider them in your management decisions.

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 (when 50% of plants have produced young pods) 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

Pea aphid thresholds in faba beans are higher than in peas. The action threshold of 34-50 aphids/main branch gives a 7-day lead time before injury levels are reached (96-142/main branch).

Additional Resources

Pea aphids in peas, faba beans and lentils – Manitoba Agriculture and Resource Development
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)