PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
NON-SELECTIVE & SELECTIVE FUNGICIDES
Broad & narrow spectrum fungicides
NON-SELECTIVE WIDE
FUNGICIDES
Broad spectrum
SELECTIVE
FUNGICIDES
Narrow spectrum
RANGE OF ACTIVITY
Many fungicides have some activity against
a wide range of fungal diseases, eg
– Copper and sulphur
– Mancozeb , Thiram and Zineb
– Zyban (mancozeb/thiophanate-methyl)
Many fungicides, especially the new systemic ones, may only be effective against
particular groups of fungi (some exceptions).
Phycomycota fungi only. These fungicides are only effective against
Phycomycota, eg
– Fongarid (furalaxyl) - Phytophthora, Pythium
– Ridomil (metalaxyl) - Phytophthora, Pythium
Not. Phycomycota fungi. Some
fungicides are not effective against
Phycomycota fungal diseases but are
affective against powdery mildews,
leaf spots, rusts and some soil diseases, eg
– Bavistin (carbendazim) - Powdery mildews, leaf spots
– Bayleton (triadimefon) - Powdery mildews, rusts
– Tilt (propiconazole) - Powdery mildews, leaf spots, rusts
– Saprol (triforine) - Powdery mildews, leaf spots, rusts, brown rot
WHEN SHOULD FUNGICIDES BE APPLIED?
GROWTH STAGE
OF HOST
Depending on the disease and fungicide type, fungicides can be applied to different parts
of the host plant. Some diseases only affect new foliage, eg peach leaf curl.
Foliage Flowers Dormant Seeds, cuttings Bulbs, corms Roots, soil
SUSCEPTIBLE
STAGE IN FUNGUS
LIFE CYCLE
Spores of peach leaf curl
’overwinter’ on buds
NUMBER AND
INTERVAL
BETWEEN
APPLICATIONS
Choose a susceptible stage in the life cycle of the fungus, eg peach leaf curl spores
'overwinter' in the buds and infect new leaves in spring (page 359).
Timing. The disease cycle determines where and when a fungicide is applied.
– Peach leaf curl can be controlled with a single application to dormant buds
before new leaves are infected.
– Some diseases may be controlled by starting applications at the very first
sign of disease, eg powdery mildews.
Early warning systems. Once conditions favouring a particular disease are
known, weather can be monitored and spore germination and infection predicted with
some certainty.
– Early warning systems are available for many crops, including downy mildew
of grapes, prune rust.
– Sometimes it is difficult to apply fungicides at the correct time, eg weather is
unsuitable for application. Inability to recognize the problem.
PEACH LEAF CURL (an example)
Follow resistance strategies on fungicide labels.
Correct number of applications is necessary to obtain satisfactory control of
many diseases. There are exceptions, eg peach leaf curl of stone fruit may be
controlled by only one preventative application of copper to susceptible trees at
early budswell and no later than mid-budswell or control will be unsatisfactory and
new leaves may be damaged. Weather may prevent this.
Correct interval between applications. For some diseases applications may
need to be made at regular intervals, which may vary according to weather, the
particular fungus and persistence of the fungicide, eg black spot of rose. Warning
systems may indicate when applications are necessary.
Preventative applications may be necessary for ‘key’ diseases that occur
every year, eg seeds, cuttings and soil are frequently treated with fungicides to
provide some control of damping off diseases.
336 Fungal diseases - Integrated disease management