PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
Control methods
Cultural methods.
Cultural practices will not control black spot
entirely but may reduce its incidence. They may
be only practical in greenhouses.
Keep humidity low
– By not planting bushes too close together.
– Avoid growing smaller plants such as
flowering annuals underneath rose bushes.
– Do not plant roses in shady situations or very
sheltered areas where air circulation is
minimal.
– Do not water plants late in the day so that
leaves remain wet for a long period of time.
Avoid overhead irrigation, eg use drip or
hydroponic systems. If overhead irrigating, do
so early in the day so foliage is dry before
evening.
Avoid overfertilizing which causes soft
growth which is very susceptible to black spot.
Mulching early in spring can serve as a
mechanical barrier between the spores formed on
old leaves on the ground and the developing
leaves overhead. However, in susceptible
varieties the fungus may overwinter on canes.
Other fungal leaf spots, eg Mycosphaerella
cryptica in Eucalyptus globulus, have been
shown to be more severe when phosphorus
levels were low.
Sanitation.
Fallen leaves. Although the fungus grows as a
saprophyte on fallen leaves and prunings, the
importance of collecting them has probably been
over-stressed. Also it is impossible to collect all
fallen leaves and in susceptible varieties, the
fungus may overwinter on the canes.
Prune out infected canes during winter pruning,
and destroy fallen leaves and prunings. Prune so
that the center of the bush is not overgrown.
In gardens, first infected leaves in spring can
be removed by hand providing foliage is dry.
Remove and destroy infected leaves,
cutting back canes of diseased rose plants. Pick
up and burn diseased fallen leaves.
Biological control.
In the USA, Rose Flora TM (Bacillus laterosporus)
has been found to inhibit the growth of the black
spot fungus and a number of soilborne fungi
including Rhizoctonia, Verticillium,
Phytophthora and Pythium in the laboratory.
To make it more effective it can be mixed with
an anti-transpirant foliar spray.
Resistant varieties.
Varieties vary in their susceptibility.
Discard very susceptible varieties if practical.
Varieties with some resistance include:
– Hybrid teas, eg 'Electron', 'First Prize', 'Peace',
'Tiffany'.
– Grandifloras and floribundas, eg 'Angel Face',
'Carousel', 'First Edition', 'Gene Boerner', 'Queen
Elizabeth', Sonia'.
Fungicides.
Fungicides may be applied to susceptible
varieties when warm, humid conditions start.
Make sure that both leaf surfaces are wetted
with fungicide.
Fungicides that control black spot will also
control anthracnose.
Excess copper applications may cause leaf
yellowing.
If predatory mites are used to control
twospotted mite then only fungicides non-toxic
to the predators should be selected.
Risk of resistance. Leaf spotting fungi of some
other crops, eg wheat, are accepted as having a
medium risk of development of resistance to
fungicides. Resistance management strategies are
available for some crops and leaf spots on the
CropLife Australia website
www.croplifeaustralia.org.au/
Check label resistance Management Strategies.
Table 65. Black spot – Some fungicides.
What to use?
Nearly all garden sprays and dusts for roses contain a fungicide
which will control black spot on roses.
POTASSIUM BICARBONATE & OILS (non-systemic)
Eco-Rose (potassium bicarbonate)
Baking soda + horticultural oil
Spray oils, eg petroleum oils
NON-SYSTEMIC FUNGICIDES (protectant)
Group M fungicides carry an inherently low risk of fungicide
resistance developing
Group M1, eg copper compounds, eg copper hydroxide,
oxychloride
Group M3, eg mancozeb; thiram; zineb,
Group M4, eg Captan , Merpan (captan)
Group M5, eg Bravo (chlorothanonil)
SYSTEMIC FUNGICIDES (eradicant)
Group 1, eg Various (carbendazim)
Group 3, eg Baycor (bitertanol), Saprol (triforine)
When and how to apply?
On susceptible varieties, the more humid the weather, the
more often it is likely that spraying will be necessary.
These sprays have little residual effect
Some of these fungicides also control rust on roses.
As soon as humid weather commences in spring
susceptible varieties may be sprayed with a suitable
fungicide at various intervals depending on the
weather, eg after each rain.
Ensure both upper and lower leaf surfaces are covered
with the fungicide.
Follow Resistance Management Strategies.
Some of these fungicides also control powdery mildew
and/or rust on roses.
Fungicide applications may begin in spring at the first
appearance of black spot on the foliage of susceptible
varieties. Repeat applications may be required after rain
(check label).
Fungal diseases - Examples of fungal diseases 357