The pea moth, scientifically known as Cydia nigricana, poses a common challenge for individuals cultivating peas. This small, inconspicuous insect is a widespread pest across Europe and parts of North America, particularly in regions conducive to pea growth. The actual damage to pea plants is not caused by the adult moth, but rather by its larval stage, the caterpillar. Understanding the life cycle and behaviors of this pest is the first step in protecting pea harvests from internal damage.
The Pea Moth Life Cycle
The pea moth life cycle spans one generation per year, though a second generation can occur in warmer conditions. Adult moths, which are dull grey-brown with distinctive white and black markings on the leading edge of their forewings, emerge from cocoons in the soil around late May to early June. These moths measure approximately 6 millimeters in length with a wingspan of about 12 to 16 millimeters.
Female moths seek out flowering pea plants and lay their tiny, flattened eggs, less than 1 millimeter in size, singly or in small groups. Eggs are deposited on the flowers, young pods, leaves, or stipules from early June until mid-August. After one to three weeks, depending on temperature, creamy-white or pale yellow caterpillars hatch.
Newly hatched caterpillars, which have a dark head and can grow up to 18 millimeters long, quickly bore into developing pea pods. Inside the pod, they feed on the peas for three weeks to a month, damaging the seeds. Once fully fed, these caterpillars chew their way out of the pods and drop to the soil. They burrow into the ground, forming a silken cocoon where they overwinter before pupating in the spring.
Signs of a Pea Moth Infestation
Detecting a pea moth infestation can be difficult because the damaging caterpillars remain hidden inside the pea pods. From the outside, pea pods may show minimal signs of damage, such as a small, discolored entry hole that is often hard to spot. Affected pods might also appear yellow or ripen prematurely.
The clearest evidence of an infestation becomes apparent only when pea pods are opened for shelling. Inside, one or more creamy white caterpillars, up to 14 millimeters long, may be found actively feeding on the peas. Along with the caterpillars, gardeners will observe webbing and small, dark pellets of excrement, known as frass, near the damaged peas. The peas themselves may be shriveled, discolored, or show irregular cavities where the caterpillars have fed, making them unmarketable.
Prevention and Control Methods
Effective management of pea moths involves strategies to disrupt their life cycle and prevent caterpillars from reaching the pods. Cultural controls offer a first line of defense, focusing on timing and soil management. Sowing peas either very early or very late in the season can help avoid the moth’s peak egg-laying period, which occurs from June to July. Tilling or ploughing the soil in the autumn exposes overwintering pupae to predators and harsh winter conditions, reducing their survival rate. Removing all plant debris after harvest also eliminates potential overwintering sites.
Physical barriers provide a direct method of exclusion, preventing adult moths from reaching plants to lay eggs. Fine insect-proof mesh or horticultural fleece can be draped over pea plants. For these covers to be effective, they must be put in place before the pea plants begin to flower and securely fastened at the edges to ensure no moths can get underneath. Since peas are self-pollinating, covering them will not negatively impact crop yield.
Monitoring moth activity with pheromone traps can inform the timing of other control measures. These traps utilize a synthetic version of the female pea moth’s mating pheromone to attract and capture male moths. Placing traps in the pea crop by mid-May and checking them every two to three days helps gardeners determine when adult moths are active and egg-laying is likely to begin. While pheromone traps are effective for alerting gardeners to the presence of moths, their primary purpose is monitoring rather than mass trapping or eliminating the entire population. The traps should be hung at canopy height and raised as the plants grow to remain effective.