In
hydroponic systems, the 3 ‘ingredients’
that must be present for disease outbreak to occur are a fungal source,
a suitable environment and a host. Therefore if you can
eliminate one or more of these ingredients it is possible to avoid disease
outbreak and / or prevent a disease from spreading. By adhering to the
following management practices you will significantly reduce the risk of
disease.
1.
MINIMISE STRESS:
The optimisation of
water and air temperature,
humidity,
light (intensity, spectrum, duration),
nutrient
concentration and pH are vital in
minimising plant stress and produces a strong, healthy plant that is best
able to defend itself against disease attack (for more information look at
our
Quick Reference Guide).
2.
REGULARLY STERILISE THE NUTRIENT AND ROOT ZONE:
This
will help ensure the nutrient delivers optimum performance.
3. HUMIDITY:
Controlling
humidity
will, for many diseases, prevent
spore germination. Keeping ‘relative humidity’ at 60-70% will offer the best
compromise for both fungal disease prevention and plant growth.
4. STERILISE MAKE-UP WATER:
Untreated surface waters
such as dam, creek, lake, etc., must be sterilised 24 hours prior to use.
New RO and scheme waters are normally sterile. Also, because the
quality of all waters deteriorate during storage, they should be regularly
treated. Further, always
store such waters in the dark.
5.
SYSTEM DESIGN:
This is vital in order to
control the quality of the nutrient at the root zone. To achieve
this, waterings must be relatively frequent and must flood the entire root
zone and medium. This will help ensure that the root zone is constantly
being rejuvenated with oxygenated nutrient that is at the correct pH and
conductivity (or concentration). This also enables salt build up and waste
material to be flushed away. Waterings will have to be more frequent during
hot weather because evaporation and increased nutrient uptake will cause the
nutrient’s conductivity to rise between each watering. Note that the ebb
and flow (flood & drain) style of recirculating system is the optimum design
for satisfying these criteria. Note, unless using an NFT system,
ensure to employ a medium that has good drainage properties otherwise roots
are likely to suffer from a lack of oxygen.
6. GENERAL HYGIENE:
Absolute cleanliness of
the growing area and tools (e.g. secateurs) is a must to minimise the risk
of disease transfer and to achieve maximum growth. Therefore, diseased
foliage / roots and general debris should be promptly removed from the
growing area. Also, surfaces must be kept clean from dust, dirt and
spillages. Minimising personnel traffic in the area and no smoking are other
worthwhile precautions.
7. INSECTS:
They feed off plants and
therefore spread disease from one plant to another via sap transfer. Use
“yellow sticky traps” to give forewarning that insects are present. If
growing indoors, minimise insect invasion by filtering all incoming air.
These must be inspected and cleaned regularly.
8. NURSERY STOCK:
Ensure seeds and media are
from a reliable source and sterile. Since an incubation period is required
for spores to germinate and become recognizable, looks can be deceiving.
Also, diseases can lay dormant for long periods of time until exposed to the
correct conditions.
9. KNOWLEDGE OF DISEASE TYPE:
This is critical if
wanting to use chemical foliar sprays because most are useful against only
one or two specific diseases. The wrong choice of spray can be costly for a
large commercial operation. It is also useful because environmental
conditions can then be modified accordingly to lower the rate of disease
spreading. Note: many diseases have similar symptoms and therefore
professional analysis may be appropriate.
