PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
NON-SYSTEMIC & SYSTEMIC FUNGICIDES (contd)
Protectant & eradicant fungicides - Movement in plants
SYSTEMIC
FUNGICIDES
Eradicant
fungicides
Curative
fungicides
ERADICANTS, CHEMO-THERAPEUTANTS.
Systemic fungicides enter a plant and are active at sites remote from where they are
applied; they are carried through the sap stream. They are often called eradicants
or chemo-therapeutants because they not only protect the host from infection
while they are on the outside, some may suppress or kill fungal organisms after
they are within the host.
Cross section of leaf
Translocated
fungicides
No spray. Spores germinate and
germ tubes penetrate leaf.
SYSTEMIC. - FOLIAGE, eg
Baycor (bitertanol)
Bayleton , various (triadimefon)
Saprol , various (triforine)
Tilt , various (propiconazole)
Spray applied after germ tubes and
mycelium are inside the host. Mycelium
already inside the leaf is killed.
SYSTEMIC. – SOIL, eg
Fongarid (furalaxyl)
Ridomil , various (metalaxyl)
Systemic fungicides and applied to the
foliage do not generally move downwards
into the roots. Their distribution within the
above ground parts of the plant is variable.
Systemic fungicides applied to the roots do
not generally move upwards to control
foliage diseases, there are exceptions. When
applied to the soil, they dissolve in soil
water and are taken up by the roots and
translocated upwards to varying degrees
within the plant. The soil must be kept moist
for continued uptake
Narrow spectrum
of activity.
Some new systemic
have a very narrow
spectrum of activity but
they work better than
the older ones
Translaminar
movement.
Some fungicides, eg
Stroby (kresoximmethyl),
are nonsystemic
but can move
into, and may to a
limited extent move
within the leaf blade.
Excessive residues
may still occur unless
withholding periods are
observed. Washing the
outside does not
remove internal
residues.
Advantages. of systemic fungicides include:
– They can reach diseases already in the host, eradicate established infections.
They can be applied after any infection period determined by environmental
monitoring stations.
– Timing is not so critical. New developing foliage may be protected without
further applications being necessary immediately.
– The whole plant surface need not be treated, eg systemic pesticides may be
applied as foliage, root and soil or tree injection treatments.
– After the fungicide has been absorbed by the plant, it is not washed off by rain.
– Surface residues disappear rapidly which minimizes risk to non-target organisms.
– Some also have quite good protectant qualities.
– Can be used to target periods when conditions are favourable for disease.
Disadvantages. of systemic fungicides include:
– Many are selective fungicides, not broad spectrum, and are usually only
effective against a particular group of fungi. There are exceptions.
– Fungal diseases may develop resistance to systemic fungicides and their
overuse is the most common way for resistant strains to be generated.
– Some systemic fungicides are not evenly distributed inside a plant but remain in
the general area of entry to the plant. Penetration into certain tissues such as
fruit and stems can be very limited. The degree of systemic activity varies but
most are absorbed by the leaves or roots and transported upwards through the
xylem (water-conducting system) and phloem. Thorough coverage is often still
necessary for control.
– They may control the disease, pest or weed more slowly than contact nonsystemic
pesticides.
334 Fungal diseases - Integrated disease management