Why Are There Worms Inside My Pea Pods?

Opening a pea pod that looks perfect from the outside and finding a small caterpillar inside — typically coiled between the peas, having eaten into one or more — is the work of pea moth (Cydia nigricana). This is one of the most frustrating pea pests because the damage is invisible until you open the pods at harvest. From outside, affected pods look identical to clean ones; inside, the caterpillar (a pale yellow-green larva, 10–12 mm) has eaten into the developing peas and left characteristic dark frass (excrement).

The pea moth lifecycle

Pea moth adults emerge from the soil in early summer and fly from late June to mid-August. Females lay eggs on pea flowers and developing pods during this flight window. Eggs hatch into larvae that bore through the pod wall into the developing peas. Once they have completed feeding (two to three weeks inside the pod), they exit the pod, drop to the soil, and pupate to overwinter. Pea moth is most damaging on late-June to August sowings, where flowering and pod development coincide with the flight period.

How timing prevents damage

The most reliable prevention strategy is to sow so that the peas are either flowering before the moth's flight begins (before late June — achievable with early sowings in March–April) or that they are still small seedlings when the moth is flying and begin flowering in September (achievable with late summer sowings of fast-maturing varieties). Peas that flower and set pods between July and early August take the full force of pea moth attack. A March sowing is harvested by late June; pea moth has not yet emerged.

Netting and other measures

Fine mesh netting (Enviromesh, 1.25 mm or finer) installed before moth flight begins and kept over the plants throughout the flight period physically prevents egg-laying. This is practical for small plantings. Pheromone traps (Cydia nigricana attractants, available from specialist suppliers) capture adult males and can be used to monitor flight period timing — allowing you to install netting at the right moment if you want precise timing rather than permanent netting.