growing season I planted parsnip seed. They grew beautifully, but
on harvesting them I found each parsnip has large brown, rotted
areas just below the crown at ground level and same further down,
too. The brown area appears to have been eaten by an insect. How
can I get rid of the problem?
sounds like your parsnips have been attacked by the larvae of carrot
rust fly. The adult is a small black fly about 4-6mm long which
lays its eggs in the soil close to where carrots and closely related
plants, like parsnips, celery and parsley, are growing. On hatching,
the young, pale, creamy maggot-like larvae feed on the very fine
root hairs of seedlings, but eventually they burrow into the main
root which can lead to secondary rots, hence the brown areas you
describe. The larvae can grow up to 8mm long.
If you want to use an
insecticide, granular diazinon, sold as Soil Insect Killer, and
applied when sowing the seed or sprinkled alongside the plants after
thinning seedlings, is effective. However, there are other ways
of reducing damage that don't involve the use of insecticides. Try
- Rotate crops - don't
plant parsnips, carrots, celery or parsley in the same soil year
after year. Allow a break of at least one season, preferably two.
- Don't leave old damaged
plants of the carrot family in the soil - remove them as soon
as practicable. And get rid of any carrot-related weeds like wild
carrot, fennel and hemlock.
- Sow your parsnip seeds
thinly or thin out closely spaced seedlings as early as possible.
- Mound soil up around
the base of the parsnips as they grow - this is claimed to make
it harder for larvae to reach the roots.
- Shelter your parsnips
under a covering of shade cloth or light insect mesh in an attempt
to stop the fly from getting to the soil around the plants to
lay eggs. Peg the mesh down to the soil about 30cm or so out from
Gardener, Issue 179, 2005, Page 30
Reproduced with permission from the former Weekend Gardener magazine. The views expressed here are not necessarily those of the RNZIH.