What's eating our parsnips

[talltony]

Anyone know what this is? Every year they decimate the parsnip crop. They're about 3cm long.
They don't touch the carrots. They're active from end of summer through the winter. We've limited the impact by pulling the crop early and freezing. That doesn't stop them coming back next year though. We skipped a year altogether and that reduced the numbers drastically but they recovered a couple of years later. The damage they do is like carrot fly but bigger.

[Martin H]

That looks like a wireworm.

[Greenleaves]

I'm with Martin on this one, wire worms are the larvae of the Click Beetle. You can get nematodes but I have no idea how effective they are

[marchogaeth]

Yep. More info here

BBC - Gardening - Advice: Pest and disease identifier

American site but ideas for organic control Wireworm Control | Planet Natural

I found this reference to using fodder beet Wireworm and Sowing Mustard

The statement made in your organic catalogue is in fact a suggestion made by the founder of HDRA. It has never been scientifically tested, and in fact runs completely counter to insect physiology: insects are cold blooded and rate of development is strictly related to temperature. Food quality and quantity may affect eventual size, but not the rate of growth.

In support of the theory that sowing mustard controls wireworm:
1. de Bairacli Levy (1966 - Herbal Handbook for Everyone)
2. G. Franck (1983 - Companion Planting)


3. L. D. Hills (1971 - Grow Your Own Fruit and Vegetables)
4. Lichtenstein, Morgan & Mueller (1964 - Naturally Occurring Insecticides in Cruciferous crops (Journal of Agriculture))
5. Parker & Howard - (2001 - paper on The Biology and Management of Wireworms - ADAS,Woodthorne)
6. J. Soper (1966 - Biodynamic Gardening)

Finally, see the ADAS paper (2001) Wireworm control using Fodder Rape and Mustard by Frost, Clarke & McLean, on field trials of (inter alia) mustard in Pwllpeiran, which indicated quite reduced levels of damage to potatoes from both wireworm and slugs on plots where mustard was sown and rotovated in after a mere 6 weeks, immediately before potato planting, compared with untreated plots.

This idea is widely quoted with references to the original paper. However, I have had a quick scan through the original paper which essentially concludes "interesting idea but not proven - needs more work." I have been unable to find any follow up experiments - never mind repeating the results. Maybe someone on here actually uses it as a method and can comment.

[Martin H]

Apparently wireworms are worst in the first couple of years. When you cultivate the soil they go away.

[marchogaeth]

I was going to ask, how long since you dug in the grass. My garden came out of a field and it took two years to really hammer the population.

[talltony]

Yes wireworms make sense.

How to get rid of them though?

The ground has been cultivated for over a decade, and I'm pretty good at keeping the weeds down including grass.

Maybe not grow susceptible crops for a year or two? Rake the soil a few times in winter to let the birds at them? Nematodes?

[marchogaeth]

So now I'm curious, what other plants do you get damage in, as you only mentioned your parsnips? I would have thought, if you are rotating your crops never mind cultivating they should be gone.

You are thinking on the right lines in terms of breaking their life cycle, IMO but this should already have happened enough so that damage is minimal. You could be spending on nematodes every year if there is a "source" that keeps topping them up.