THREE
ONION FLY OR ONION WHITE ROT?
You’ll probably never see an onion fly. It’s small, grey, and
unremarkable. You’ll notice the damage its larvae cause,
though. They work out of sight, munching through onion,
shallot, and garlic bulbs to reduce entire beds to soft, rotten
mush just as they reach their peak. However, onions can
also rot mid-season from another, more sinister cause. Onion
white rot is one of the most persistent fungal diseases. It
produces pinhead-sized black resting bodies known as
sclerotia, which survive in the soil for 15 years or more,
reinfesting and ruining each successive crop.
FOUR
SLUG DAMAGE OR DAMPING OFF?
Telling them apart:
The first symptoms are superficially the same: leaves
wilt and turn brown and the top of the bulb begins to rot.
Dig up an affected bulb, though, and look closely. White
rot begins at the base of the bulb, spreading upwards
from the roots. Onion fly maggots, however, start at the
top and work down. You’ll sometimes also see them
wriggling in the top of the bulb.
Treatment:
Onion Fly: Lift the damaged bulbs and burn them to kill
the maggots. Rotate crops into clean ground each year, and
plant under mesh to prevent adults laying their eggs.
Onion White Rot: White rot is almost impossible to get rid of
once established, so prevent it by buying seed and sets from
a reliable source. Good garden hygiene helps too. If you
have infested ground, grow onions in containers instead.
56
Maximum Yield
A gardener never tires of that magical moment when new
seedlings unfurl from the compost for the first time. So, when
your seed trays stay resolutely empty or produce just straggly
patches of weedy, sorry-looking shoots, it hits you right where
it hurts. Your local slug population may have discovered
there’s a fine new meal to be had, munching away your new
shoots the moment they poked their heads above ground. Or
your babies may have succumbed to damping off, a vicious
fungal pathogen capable of destroying a tray of healthy
seedlings within hours.
Telling them apart:
Slugs leave a tell-tale trail of slime wherever they go, so
this is your giveaway for a slimy mollusc attack. Damping
off, on the other hand, is a fungal disease. When it attacks
seedlings after they emerge, you’ll see their remains on the
surface, often covered in white, fluffy mold. Pre-emergence
damping off happens below compost level, so your
seedlings simply fail to come up.
Treatment:
Slug Damage: Check your seed trays daily, especially
when it’s damp, to search out and destroy lurking slugs.
Wildlife-friendly ferrous phosphate slug pellets also help.
Damping Off: Use sterilized seed compost and clean
containers, and sow seeds sparingly to allow lots of air
circulation between the resulting seedlings. Don’t water
with rainwater, which can carry disease, and keep trays
damp but not soggy.