The Big Pea Moth Challenge

I have been attempting to grow peas now for 3 years and each season I always have pods of peas infected with the maggoty larvae of the Pea Moth!

peas
Is the dreaded Pea Moth caterpillar lurking inside?

Last year, early sowing of peas gave me a harvest free from pea moth caterpillars but later sowings led to an infestation of epic proportions! And there is not much I can do in terms of biological or chemical control either. One book I read suggested spraying with general insecticide when flowering to prevent the moth from laying its eggs. I did try this but it didn’t seem to have an effect and I would rather not do this again as I worry about the harm it will do to beneficial pollinators! I have also read about using pheromone traps as a warning system for when to protect your crops and then covering the crop with netting or fleece. I did try covering the peas but the little buggers still found there way inside although after a particularly windy day – the fleece was no more.

So this year, I am conducting an experiment (this is what happens when you put a scientist in the garden!) to try and ensure that I don’t waste my time growing peas that I will inevitably be unable to use!

A little bit of background on my small yet mighty foe…

The Pea Moth

The Pea Moth is a very small brown moth that overwinters in a cocoon in the soil. They emerge from this cocoon in May and June and lay their eggs on pea flowers June-July. The larvae hatch from the egg and move into the developing pea pod where they munch their way through the peas leaving trails of excrement (frass). As the larvae mature, they burrow out of the pod (if left unpicked) and drop to the ground where they will over winter – completing the cycle.

It is unlikely that you will spot the eggs on the flowers and the first sign that there has been an infestation is when a pod is opened to find the creamy white black headed caterpillar munching away.

Although this tells me which period the moth is active, what I want to know is how this relates to sowing time. Which sowings will lead to pea moth infestation?

Armed with this knowledge, I am going to set up the following experiment:

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Aim: To determine when pea crops are most likely to be infected with pea moth larvae in my area

Method: Peas will be sown at 7-14 day intervals between March and August up to a total of 20 sowings. Each sowing will be of 20 peas and will be labelled with the variety and the date of sowing. Once peas are 5-7cm tall they will transplanted to their final growing positions and plants will be labelled with their date of sowing. Peas will be monitored for signs of flowers and the date recorded when peas first start flowering. At harvest time, pods will be picked and kept in groups according to their sowing date. Peas will be podded and the number of pea moth larvae present will be recorded.

This is just a simplified version of my experiment. I know it is going to be far more complex to carry out. What I hope to achieve from this is an idea of which sowings and/or flowerings are likely to result in an infected crop so that I can take precautions to avoid this from happening in the future!

As I will have a lovely new polytunnel by the end of the year, I hope that by identifying which sowings lead to pea moth infestation means I can plant these plants in the polytunnel which may afford greater protection from the Pea Moth.

I also hope to gather quite a bit of data from this experiment generally on peas and their growth characteristics as well. It will interesting to see how their germination rate differs throughout the six month period!

A second experiment may be conducted if I have the time and space to do so as I would like to know if pheromone traps can be used to reduce the likelihood of infestation.

trap
A pheromone trap!

Aim: To determine if pheromone traps will  reduce the number of pea moth caterpillars in pods.

Pea plants bought from a garden store will be planted in the beginning of May to ensure a flowering period during pea moth activity. They will be planted in a separate plot from the first experiment and a pheromone trap will be placed among the peas from Mid May to July. Traps will be monitored every 2-3 days and numbers of pea moth found will be recorded. Pods will be harvested and numbers of pea moth caterpillar recorded and compared to numbers found in experiment 1.

I’ll keep you updated with the experiment as it progresses!

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