PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
NON-SYSTEMIC & SYSTEMIC FUNGICIDES
Protectant & eradicant fungicides - Movement in plants
NON-SYSTEMIC
FUNGICIDES
Protectant
fungicides
PROTECTANTS.
Non-systemic fungicides are not absorbed by plant tissue and are
only active at the site of application (contact between the fungicide and the
fungus). They are often called protectant fungicides because they protect the
host plant from initial infection and further infections.
Most fungal spores infect the host during wet weather, the wet surface of the
plant providing a suitable ‘seed-bed’ in which spores can germinate. When the
plant is coated with a fungicide, some of the chemical will dissolve in the water on
the surface of the host and the spores are killed before they can enter the host.
Coverage must be thorough, make sure there is time for it to dry on the foliage.
Because protectant fungicides are non-systemic, they only kill fungi on
the outside of the host, they will not kill the fungus once it is inside the host plant!
The fungicide must be applied before the spores land on leaves!
Cross section
of leaf
No spray. Spores
germinate and germ
tubes penetrate leaf
Spray applied after
spores have germinated.
Germ tubes and mycelium
already within the leaf are
not killed
Spray applied before
spores land on leaf.
Spores are killed on the
outside before germ
tubes penetrate leaf.
NON-SYSTEMIC. - FOLAGE, eg
copper hydroxide
copper oxychloride
mancozeb
sulphur
NON-SYSTEMIC. - SOIL, eg
Previcur , various (propamocarb)
Terrazole (etridiazole)
TMTD , various (thiram)
. Advantages. of non-systemic fungicides include:
– Often cheaper than systemic fungicides.
– Less toxic (there are some exceptions).
– Limited fungicide resistance.
– Usually affect a number of metabolic pathways in the fungus, and tend to have
a broad spectrum of activity.
Disadvantages. of non-systemic fungicides include:
– They must be applied before the arrival of the disease organisms, before
symptoms are apparent or when the first symptoms appear. It must be applied
before the fungus has actually been found but where it is expected.
– All the foliage must be treated.
– Rain or very windy weather may prevent fungicides being applied at the right
time, so control may be difficult to achieve even with an effective fungicide.
– The fungicide remains on the outside of the plant and so may be toxic to
beneficial or other harmless organisms.
– Regular applications may be necessary when plants are growing actively to
protect new growth and because rain may wash protectant fungicides off the
plant or they may deteriorate due to heat, light and rain.
Fungal diseases - Integrated disease management 333