The Zimbabwean Gardener Issue 3 Summer 2012 | 页面 7

Summer flowering annuals
Impatiens walleriana, commonly
known as Busy Lizzies, have long been
a favourite summer annual for many,
as the wide range of colours available
provide cheer in your garden during
the festive season. Unfortunately in
Zimbabwe and worldwide, our Busy
Lizzies are now under threat from
Downy mildew, which can kill your
Busy Lizzies quickly. However, if you
put in the time and stick to a religious
spraying routine, your Busy Lizzies will
last through the season and you will be
rewarded with a wonderful splash of
colour in your garden.

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What is Downy mildew?
Downy mildew is a disease of the
foliage, caused by a fungus-like
organism. It is spread from plant to
plant by airborne spores and the
disease favours prolonged leaf wetness.
Therefore, it is more prevalent in wet,
humid weather; in Zimbabwe, these
weather conditions are ripe for Downy
mildew around Christmas time. The first
symptoms of Downy mildew in Busy
Lizzies are small pale green leaves,
down curling and distortion of leaves,
white powdery growth on the underside
of the leaves and stunted growth.

What to do if your plants have
Downy mildew on them

Downy mildew causes stunted growth
and pale green leaves.

How to control Downy mildew
If you want to enjoy the splash of colour
in your garden, it comes at a price as
the only way of controlling the Downy
mildew is by spraying and treating your
soil correctly. Here is a guide to follow
when planting them this year to avoid
Downy mildew.

1

If you plan to plant Busy Lizzies in
the same bed or pots as last year,
either change your soil or sterilise
the soil and your pots with Jeyes fluid.
Drench the soil with a mixture of Jeyes
Fluid solution of 10 ml per 10 litres
of water. Leave the bed for 2 days
preferably under plastic cover before
digging over. Dig over and water again.
Apply a handful of Superphosphate per
square metre and dig into the bed to a
depth of 30 cm.

If your plants have already been
affected with Downy mildew, remove
them immediately or if they are not
too badly infected, cut off the diseased
leaves and spray the remaining plant
with Ridomil weekly. Place infected
plants in plastic bags, tie them up and
place in the rubbish bin. It is important
to gather all the affected plants from
the bed. Do not compost the affected
plants either. Do not replant Busy
Lizzies in the same area unless the soil
has been treated. Unfortunately, the
disease is now in Zimbabwe and the
spores have the ability to spread long
distances in air currents. Practise proper
plant hygiene and clean up your beds to
prevent it from spreading more.

How to grow Busy Lizzies
Plant your Busy Lizzies 30 cm apart in
semi shade to full sun; in the extreme
heat, they can get a bit ‘sunburnt’ if in
full sun and their petals fade slightly.
Avoid planting them in full shade, as
they will become leggy and more likely
to get Downy mildew. If your Busy
Lizzies do get leggy, pinch them back;
make sure you pinch them back just
before a leaf.

2

Spray or drench plants fortnightly
with Phosguard or Phosphite at a
rate of 20 ml to 10 litres of water.
This mixture will help to protect the plant
against Downy mildew as it also fertilises
and strengthens the plant. Personally, I
wouldn’t just rely on spraying this alone
– I would also spray with Ridomil Gold.

3

Ridomil Gold is a must! It is a
very good systemic and contact
fungicide for the control of Downy
mildew. Drench the root zone of each
plant using 25g per 10 litres, shortly
before the disease is expected in
December. Apply weekly during the rains.

4

If you have decided not to spray,
then take care to prevent prolonged
leaf wetness by watering them
in the morning so they are dry by the
evening.

One symptom or Downy mildew is a
white powdery growth on the underside
of the leaves.

5

To avoid infection from soil-borne
resting spores, avoid re-planting
them in the bed that has been
affected for at least a year or two.

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