The parsnip seed project looks to be a success this year. Plants left in the ground over winter are happy to turn the energy stored in their delicious roots into vigorous growth in the spring. The parsnips were one of the first things to green up in the spring, and now they have the record for the tallest plants in the garden.
Parsnips don’t have many pests because the plant manufactures its own insecticide, chemical furanocumarins. Their roots are much more resistant to pests than are carrots over the winter. Hence, I was surprised when I discovered quite a few caterpillar nests in the emerging seed blooms a few weeks ago. It turns out parsnips do have a specific pest, the parsnip webworm, that can be a problem. The caterpillars spin webs that hold the flower umbels together in a tight silk/parsnip-flower nest. The developing flowers provide food for the worms, and the nest provides protection from predators.
Prof. Berenbaum and her group at the University of Illinois have studied parsnip webworms in some detail. They have a very informative web page with lots of information on these creatures. Notable is discussion about a recent invasion of the parsnip webworm in New Zealand. Parsnips have been grown in New Zealand for about 150 years without the webworm pest. Over time, the parsnips have lost some of their chemical defenses to their enemy. As a result, the plants in New Zealand are being devastated, with plants often producing no seed at all. It is expected that this strong selection pressure will quickly produce plants with more furanocumarins in the flowers to provide some resistance to the webworms.
After figuring out what I was dealing with, I ripped apart some of the webs and picked out the worms. But I didn’t get them all. The larva eventually burrow down into the center of the main stalk where they pupate and eventually hatch out as adult moths. I am no longer seeing the larva, so presumably they are all hanging out inside the stalks at this point. I’ll investigate further when it’s time to harvest.
The worms ate some seed, but there is still plenty left to make a good crop.
Squash Practice 
How many did you plant Gary? And did you start from seed?
We had a wind storm yesterday that decimated my corn. Knocked everything flat to the ground. I may be able to salvage most of it. But it really wreaked havoc.
Hi Bo,
I planted a long row last year with the plan that some would be food and some would be seed this year. Since parsnips are outbreeders, you want ~30 plants minimum to keep the diversity up. I probably have about 25 plants in my seed patch. But this years crop is also from the original seed, so I’ll be combining alternate years seed to maintain diversity with fewer seed plants each year. Next year’s seed crop (and this winter’s food crop) is just beginning to develop roots over in another section of the garden.
Ideally, it’s best to dig everything. Do a big tasting of bits from the raw parsnips, and just plant the yummy ones for seed. That’s a bit daunting of a project, but maybe next year…
Sorry to hear about your storm damage. Everything was doing so splendidly! I guess that’s the hazard of that warm moist gulf air that make New York a jungle in the summer!
Hi- I have similar parsnips in my garden and have been juicing the greens with kale and carrots. Now I am seeing that some people believe parsnips greens to be toxic. What have you been doing with yours? Also, I planted them as part of my butterfly theme- host plant for the Eastern Black Swallowtail.
Hi Fury, Yes, the greens of the parsnip plant are actually quite nasty. Some people get a bad rash just from touching them. The parsnip makes than natural insecticide which is why nothing eats the plants but the parsnip web-worm, that has managed to figure out how to digest it. But since you are not a web-worm – I would not recommend eating the greens – especially raw.
Tell me more about the Eastern Black Swallowtail, I’m curious – why parsnips?