PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
Practice crop rotation in the field, strains of
damping-off fungi can develop. Rotate crops every 5
years or as recommended to reduce build-up of root
rot fungi in soil. Maintain good soil fertility.
Added organic matter can stimulate growth of
antagonistic soil micro-organisms.
Soil-less mixtures and hydroponic mixtures
are unfavourable to damping-off diseases spread
mainly by soil, eg Phytophthora, Pythium,
Rhizoctonia.
Osmopriming (controlled hydration of seeds) is
promising, as is replacing most of the peat in
mixtures with composted tree bark. Both reduce
root rot caused by Pythium and other root pathogens.
Do not mow or traffic wet turf surfaces, reduce
thatch by scarifying and tyning, carefully control
moisture on any newly seeded areas.
Sanitation.
Practice hygiene to prevent introduction in
potting media, cuttings, tools, personnel, water.
Prevent soil on floors contaminating benches
and growing containers.
Use only freshly made disinfectant solutions,
when required (used solutions may not work).
Store all treated equipment, containers etc in a
clean area or away from dirt and contamination
until required.
Discard and destroy any batches of badly
affected seedlings, cuttings (and soil), in an area
away from other plants.
Where hoses are used for irrigation keep
nozzles off the ground to prevent contamination.
Remove all dirt and organic matter (including
roots and sap) from surfaces, then thoroughly wash
surfaces (benches, tools, equipment, trays, pots),
prior to treating them with a disinfectant at the
concentration and time recommended.
Biological control.
Natural controls include:
– Binucleate Rhizoctonia, Pythium.
– Soil bacteria and other micro-organisms.
Commercially available.
– Trichopel (Trichoderma sp.) may be a hyperparasite.
Trichoderma atroviride can help prevent Phytphthora,
Rhiozctonia, Pythium, Fusarium.
– Companion (Bacillus subtilis) may suppress
development of Pc, Pythium, Rhizoctonia and
Fusarium on some seedlings.
– Mycostop (Streptomyces griseoviridis) overseas is
used against Fusarium, Pythium, Pc, Botrytis, etc.
– See pages 329, 344 (Table 60), 369, 374 (Table 68).
Disease-free media.
Use soilless media in nurseries or treat it.
Disease-tested planting material.
Take cuttings from vigorous disease-free stock plants.
Some damping-off fungi, eg Rhizoctonia, may be
seedborne on some hosts. Where damping-off is
seedborne and a problem on susceptible plants, eg
beans, tomatoes, etc:
– Use high quality disease-tested seeds.
– Collect seed from vigorous disease-free stock plants.
– Treat suspect seed with hot water or chemicals.
Physical & mechanical methods.
Soil pasteurization is a pre-plant treatment
for container-grown plants, eg seedling trays, not
for open beds in the field. Standard treatment is
60 o C for 30 minutes which kills most fungi that
cause damping-off. Prevent infested soil from
re-contaminating pots, potting mixes, cuttings,
germinating seeds and seedlings on benches
(page 330).
Soil solarization prior to establishing seedbeds,
correctly implemented, kills a range of disease
organisms but leaves many beneficial’s intact, like soil
pasteurization (pages 330, 438).
Hot water seed treatments. Damping-off
fungi may occur on, or in seed. If suspected, seek
advice on treatment as accurate temperature control
is essential.
Water treatments are usually only needed for
surface run-off water, eg from streams or dams and
for recycled water. Bore water, roof run-off water
and town water is usually free from damping-off
organisms and suitable for use without treatment.
Choose the right method of disinfesting water for
your situation. The following are examples of some
treatments may be used singly or in combination:
– Chlorination is a cheap and effective means of
treating water to kill damping-off organisms. Most
town water supplies are chlorinated and so free of
disease organisms. The 3 main sources of chlorine
used are calcium hypochlorite, sodium hypochlorite
and chlorine gas.
– Filtration to remove disease organisms is effective
if the mesh size is of the recommended microbiological
standard. Inclusion of a pre-filter in the
system may be an advantage (Handreck and Black
1994). Slow sand filters are still being researched
in Australia.
– Ultra-violet (UV) lights are available to sterilize
water by flowing the water around a UV tube. The
UV machines must be calibrated to produce the
dose required to kill off all damping-off fungi.
– Disinfectants (pages 340, 343).
Fungicides.
Fungicides only suppress damping-off
especially if plants are weakened by high soluble
salts and a saturated environment. The fungus is not
eradicated. Phytotoxicity may be a problem.
Identify the fungus causing the problem.
In past times, the species of fungus causing dampingoff
was often not known. This meant that fungicides
were alternated or mixed in successive treatments.
Many nurseries have regular fungicide treatments, eg
weekly or fortnightly, depending on plant species, the
specific damping-off fungi and available fungicides.
Seed treatments.
– Protective seed treatments. Many seeds, eg
peas, are coated with fungicide (and insecticide)
before being sold to prevent attack by damping-off
fungi (and insect pests) in the field (page 374,
Table 68).
– Systemic seed treatments include metalaxyl and
fludioxonil (page 374, Table 68).
– Combinations. Often several fungicides are
formulated to provide good control of damping off.
– Seed treatment is sometimes followed by
spraying seedlings with the same or different
effective fungicides than those used for seed
treatment (Agrios 2005).
Water treatments
– See Physical & Mechanical methods above.
Media/soil treatments
– Fungicides may be incorporated into potting mixes.
– Fumigation (page 267, Table 52.
Follow CropScience Australia Resistance
Management Strategies (pages 331, 337)
If purchasing seedlings, check their management
history before buying - if not treated for damping off
within the last month then consider treatment.
Fungal diseases - Examples of fungal diseases 373