PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
Management (IDM)
Are you a commercial grower or home gardener?
1. Access/prepare a plan that fits your situation. IDM
programs are available for downy mildews of many
crops, eg lettuce via AUSVEG. Also check Ausvit,
Cropwatch, State Depts. of Primary Industry.
2. Crop, region. Recognize variations.
3. Identification can be difficult without a microscope.
Consult a diagnostic service (page xiv).
4. Monitor and detect disease and/or damage on
susceptible species/ varieties from spring onwards, record
results (page 327). Do you know when, where, what
and how to monitor for your situation.
Inspect upper and lower surfaces of new leaves at least
once per week for spotting or discolouration of the most
susceptible cultivars. Will need a magnifying glass. Also
check fruit if necessary.
Warning services/Disease predictive models are
available for some crops, eg onions, grapes, lettuce, nursery
seedlings. As each downy mildew species has specific
weather requirements for successful sporulation and
infection, eg leaf wetness, temperature and rainfall, disease
forecasts can be made reducing fungicide use. Some also
provide management advice.
5. Threshold. How much damage can you accept? Have
any thresholds been established? If so, what are they, eg
economic or aesthetic? Do you need to calculate your
own threshold for your crop in your region?
6. Action. For some crops, property freedom and
prescribed treatments may apply. Check your situation.
7. Evaluation. Review your program compare current
records with earlier ones. If required, put improvements
in place, eg using resistant varieties, different fungicides.
Control methods
Downy mildews can be difficult to control.
Cultural methods can reduce the incidence by
80-100%. In glasshouses regulate temperature and
humidity to reduce night-time humidity by ventilation,
heating, air movement.
Irrigation. Keep crop as dry as possible. Spores need
water to germinate on the leaf surfaces to infect plants.
Do not overwater and avoid overhead irrigation. Irrigate
late in afternoon allowing time for leaves to dry before
dew forms on leaves. Do not water seedlings in
morning when spores are released and infect plants.
Consider capillary watering which does not wet foliage.
Maintain good ventilation to lower humidity,
minimize spore production on infected plants and
spore germination on new plants. Space and plant
rows along direction of prevailing winds to reduce
infection. Space seedling trays to improve ventilation
and dry the leaf surfaces quickly.
Maintain even temperatures.
Nutrition. Adequate potash (K) reduces seedling
susceptibility to downy mildew, eg on cauliflowers.
Controlled mostly in production with balanced nutrients.
Use a crop rotation of 2-3 years for susceptible
field crops where practical. Rotate propagation areas.
Sanitation.
Rogue and burn/deep bury diseased seedlings to
eliminate sources of infection. Remove heaviliy
infested seedling trays, old seedlings, weeds.
Plough in field crop debris immediately after harvest.
Before planting new crops remove crop debris,
destroy self-sown volunteer plants and regrowth of
annuals and weeds from previous crops and bury or
incinerate it. Disinfect propagation areas and
equipment with a short persistent disinfectant. Keep
production areas clean. Fallow glasshouses.
Prune out/destroy diseased branches on woody hosts.
Resistant varieties.
If downy mildew is a problem select varieties with
some resistance to new strains of downy mildews, eg
lettuce.
Plant quarantine.
Property freedom, prescribed treatments.
Isolate stock plants especially when first introduced
into the nursery, eg petunia.
Disease-tested planting material.
Do not propagate from infected perennial plants.
Only purchase and plant disease-tested seeds or select
seed only from healthy plants or treat seed, diseasefree
seedlings or bare-rooted nursery stock.
Physical & mechanical methods.
Pasteurization of soil in seedbeds is recommended but
is not economical for larger areas.
Research indicates that blue wave lengths of light can
help in reduction of downy mildew of cucurbits
Fungicides.
Fungicide-resistant strains of downy mildews
are present in many districts, eg downy mildew of
peas has developed resistance to metalaxyl.
Risk of resistance. The downy mildews of grapes
and cucurbits are accepted as having a high risk of
development of resistance to fungicides, while the
downy mildews of lettuce and certain other plants have
a medium risk. Resistance management strategies are
available for control of downy mildew of cucurbits,
grape, lettuce and onion on the CropLife Australia
website www.croplifeaustralia.org.au/
Spray programs for the control of downy mildew
of grape vines is also available for commercial
growers from Cropwatch in Riverland, Hort Hotline in
Sunraysia.
Check label Resistance Management Strategies.
Use Disease Prediction Services which allow
fungicide applications to be better timed, reducing
fungicide use in low risk seasons.
Thoroughly spray lower and upper leaf surfaces.
Soil fumigation for production areas of potting soil
will eliminate soilborne infection which could be
significant where the same crop is grown repeatedly.
Some plants, eg lettuce, are difficult to spray
effectively.
Table 62. Downy mildews – Some fungicides (check on particular DM
What to use?
NON-SYSTEMIC FUNGICIDES (protectants)
Group M1, eg copper hydroxide; copper oxychloride;
copper ammonium acetate
Group M3, eg zineb; mancozeb (often formulated with
systemic fungicides); Phytan , Banvel Polyram
(metiram)
Group M5, eg Alert , Bravo , various (chlorothalonil)
SYSTEMIC FUNGICIDES (eradicants)
Group 4, eg Fongarid (furalaxyl); Ridomil (metalaxyl)
Group 11, eg Amistar (azoxystrobin) (controls both
downy and powdery mildews)
Group 40, eg Acrobat (dimethomorph) - locally systemic
Group 33, eg Alliette (fosetyl-al); Fol-R-Fos , Phospot ,
various (phosphorous acid)
SEED DRESSINGS
Group 4, eg Fongarid (furalaxyl); Rampart , Mantle
(metalaxyl); Apron (metalaxyl-M)
When and how to apply?
Apply before infection occurs for best results.
Make sure undersurfaces of leaves are wetted.
M3 and M5 fungicides are often used on seedlings
which might be damaged by copper sprays.
Adjuvants such as Synetrol, Codacide, Agridex or
DCTron can provide strong activity.
Follow Resistance Management Strategies on
labels.
Keep systemic fungicides for conditions that are
particularly favourable for disease.
Systemic and contact fungicides may be combined.
Many new products being developed
Many new seed treatments are being developed (page 374).
350 Fungal diseases - Examples of fungal diseases