PLANT PROTECTION 1 – Pests, Diseases and Weeds

Control methods
Cultural methods.
Keep relative humidity low at < 85%. Avoid
overhead irrigation to assist control. Use drippers.
Space/trellis/prune plants to allow good air
circulation and penetration of sunlight.
Avoid heavy nitrogen applications since young
succulent tissue is more susceptible to infection.
Ventilate and or heat glasshouses in the evening to
reduce humidity levels by removing moist air
which builds up during the day. Prevent
condensation of moisture on leaf surfaces.
Hosing down plants over 2-3 days in the morning
may limit spread but favour Botrytis.
Avoid clipping hedges of susceptible varieties of
Photinia or Euonymus if disease is a problem.
Rotate crops every 3-4 years to reduce incidence
and severity in subsequent crops.
Sanitation.
Destroy diseased crop residues, prunings and
infected held over plants, volunteer plants.
Prune out and destroy during winter all infected
shoots on woody hosts, eg roses, apples. On apple,
also prune off and destroy mildewed shoots as they
appear during the growing season.
Pick off and destroy first infected leaves regularly
and immediately seal in a bag. Could delay an
epidemic. Do not compost.
Discard heavily infected transplants before they
reach the main greenhouse.
Biological control.
Not very practical, but natural controls include:
Fungi, eg Sporothrix flocculosa, Ampelomyces
quisqualis (BC AQ10) and Tilletiopsis spp., provide
some control of powdery mildew of roses overseas
under certain conditions.
Fungus-eating ladybirds/larvae (Illeis galbula)
feed on powdery mildew of cucurbits. Some Stethorus
beetles feed on fungal spores. Tydeid mites, living
in tiny hair-like structures on undersides of wild grape
leaves, feed on powdery mildew.
Table 61. Powdery mildews – Some fungicides...
What to use?
BIO-FUNGICIDES (non-systemic)
The following reduce the severity of powdery mildews:
Group M2, eg Eco-fungicide , Eco-carb ,Eco-rose
(potassium bicarbonate)
Whey (waste cheese), dilute to one-third of normal strength
Full cream milk - dilute to one tenth of normal strength
Milk products may not be permitted on some crops as
lactose intolerant consumers may have an allergic
reaction to plants sprayed with milk products.
Products being researched include azaradachtin (neem),
jojoba oil, garlic extracts
NON SYSTEMIC FUNGICIDES (protectant)
Group 13, eg Legend (quinoxyfen)
Group M1, eg copper compounds (limited use if disease
pressure is high (residual)
Group M2, eg Sulphur Dust (elemental sulphur);
Wettable Sulphur (dispersible sulphur);
Lime Sulphur (polysulphides)
Group M3/M2, eg Mancozeb Plus (mancozeb + sulphur)
Summer spray oils, eg D-C-Tron Plus (petroleum oil)
SYSTEMIC FUNGICIDES (eradicant)
Wide range of systemic fungicides but only a few
are registered for use on any particular crop.
Group 1, eg Bavistin , Spin (carbendazim)
Group 3, eg Anvil (hexaconazole); Baycor (bitertanol);
Nustar (flusilazole); Tilt (propiconazole);
Saprol (triforine); Systhane (myclobutanil)
Group 5, eg Prosper (spiroxamine)
Group 11, eg Amistar (azoxystrobin);
Flint (trifloxystrobin)
SEED DRESSINGS
Fungicides to control powdery mildew on some crops, eg
cereals, may be formulated with insecticides.
PLANT PROTECTION 1 – Pests, Diseases and Weeds
Resistant varieties.
If possible, grow varieties with some resistance, eg
Photinia. Varieties with some resistance include
P. glabra robusta. Very susceptible species include
P. serrulata.
Apple. Varieties with some resistance include Granny
Smith and Delicious. Very susceptible varieties include
Jonathon and Rome Beauty.
Grapevines. Most susceptible wine varieties
include Cabernet Sauvignon, Chardonnay, Chenin
Blanc, Muller Thurgau, Muscadelle, Riesling,
Semillon. Most susceptible table varieties
include Cardinal, Flame Seedless, Red Globe.
Defense-activating compounds are being
researched.
Plant quarantine. AQIS periodically may
reassess the quarantine status of some powdery
mildews to see if treatment is still required.
Disease-tested planting material.
Only plant disease-tested seed, or treat seed.
Fungicides.
Fungicides which control powdery mildew, often do not
control many other diseases. Exceptions.
In some vineyards, powdery mildew may be controlled
mainly by regular applications of sulfur and synthetic
fungicides and in organic agriculture by sulfur and
botanical and mineral oils. Milk, whey and mixtures of
botanical oil plus bicarbonate are potential replacements
for synthetic fungicides and sulfur for powdery mildew.
Apply at the first signs of disease as infection spreads
rapidly. On susceptible varieties you may need to
spray regularly at intervals depending on weather.
Thoroughly cover both leaf surfaces.
Powdery mildew mycelium is ‘hard-to-wet’, a wetting
agent may be necessary. Use a fine mist.
Treating seed of some crops, eg barley, delays onset
and reduces severity of disease.
Risk of resistance. Powdery mildew of cucurbit is
accepted as having a high risk of developing
resistance to fungicides, while powdery mildews of
apple and grapevine have a medium risk. Resistance
management strategies are available for some crops and
powdery mildews on the CropLife Australia website
www.croplifeaustralia.org.au/
Check label Resistance Management Strategies.
When and how to apply?
Some bio-fungicides may cause leaf spotting on some
cultivars if applied at higher than recommended rates, too
often, or at high temperatures. Must be good coverage.
Mix Eco-fungicide with Eco-oil to increase effectiveness.
Bicarbonate, oil, milk and whey are not preventative as they
work directly on the spores and mycelium, causing them to
shrivel up (they are contact fungicides). They often have to
be applied at 7-14 day intervals. Too much milk encourages
sooty mould.
Sulphur may damage some plants > 30 o C, especially flower
petals of some ornamentals. Can be volatilized from hot plates
in greenhouses. May leave unacceptable residues on foliage.
Sulphur can also kill of beneficial insects and mites.
Lime sulphur may be applied during dormancy after pruning
Products purchased by home gardeners often include
sulphur, eg rose or vegetable sprays and dusts.
See spray oils page 61.
Follow Croplife Australia Resistance Management
Strategies and any label instructions.
At harvest when most protection is needed it is preferable
to rely on the newest and most effective systemic fungicide.
Keep other fungicides for less risky stages.
Amistar (azoxystrobin) is effective against both powdery
and downy mildews.
Some fungicides only registered for useon only one crop,
eg Domark (tetraconazole) for powdery mildew on
grapevines.
See also page 374.
Fungal diseases - Examples of fungal diseases 347