ARISAEMA-L Digest - 13 Nov 1999 to 21 Nov 1999 (#1999-162)

[DX Victor]

Marc,

I've had quite a lot of trouble with sciarid fly over the past couple of
seasons, which I believe to be the source involved here.  They are small
flys, a couple of millimetre long, which can be seen hovering around the
soil surface or walking fast across it.  The are likely to be found in
greenhouses or around house plants, particularly where the compost is warm
and moist and where algae have formed on the surface.  They are often
encountered where the compost contains humus/peat.  They lay eggs which
produce small worms/ maggots which are up to 6mm long and wiry.  It is this
grub which does the damage, particularly to the fine roots of
seedlings/cuttings and sometimes to bulbs, such as Cyclamen and Aroids.
Grugs pupate after three weeks and adults emerge after a further week, the
whole life cycle taking about four weeks in the summer.

The pests are attracted to rotting vegetation, so a clean area is a good
starting point: Much of my problem grew from a pile of moist, dirty pots
sitting outside my main greenhouse during the summer months which acted as
a breeding ground, supplying the flies into the greenhouse.  Just shows how
careful you need to be!

There are a range of protective measures ranging from soil-mix
insecticides, such as imidacloprid, sprays, such as bifenthrin or
pyrethrum, yellow sticky traps, and smoke cones of permethrin.  I have
recently used a predatory mite called Hypoaspis miles, which is applied to
the soil.  The larvae and adults feed on the young sciarid larvae and, with
a plentiful supply of food can be active for 4-5 months.  However, for
success you need an ambient temperature in the 60's, so this is not a good
time of the year to be starting on this system.

There is a good leaflet available from the Royal Horticultural Society
Wisley for those of you who are members.





Best Regards,
David Victor

Saxifragaceae, Geraniaceae, Arisaema, Cape bulbs, Paeonia, Salvias, Irids
and anything else that is beautiful

Hockliffe, Bedfordshire, England, UK
Zone 7