PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
CONTROL
METHODS
Fungal diseases are probably easier to control than any other group of diseases, but they
are still costly and losses can be great. Most fungal diseases require an integrated
approach, no one method is sufficient.
LEGISLATION
Relevant Acts regulating the control of fungal diseases include Seed Acts, Plant
Quarantine Acts and Pesticides Acts. Food Acts regulate food, eg the maximum amount
of aflatoxin permitted in peanuts (produced when peanuts are infected with particular
species of fungi).
CULTURAL METHODS.
Provide optimum conditions for crop growth and unfavourable conditions for disease.
Generally a healthy plant withstands diseases better
Favourable conditions for plant growth.
– Choose a geographic location suited to the crop.
– Crop rotation is only useful for fungal diseases that do not survive for long in the
soil or in plant residues. Brassica rotation crops, eg mustard, canola, release
volatile gases toxic to many organisms, eg take-all fungus on wheat (page 321).
Check whether diseases may be carried over when continuously cropping.
– Planting site. Do not plant susceptible crops in soils known to be infested with
diseases, eg Sclerotium stem rot, or in poorly drained, eg Phytophthora spp.
Parsnip planted in alkaline soils encourages Rhizoctonia scab.
– Sowing/planting dates. Keep up-to-date with new research, eg short season
sunflower crops sown into in soil infested with Sclerotinia minor before mid-
November in north Victoria yielded more than later sown crops.
– Maintain recommended day and night temperatures, humidity and light for
optimum crop growth.
– Maintain recommended fertilizer programs. High nitrogen levels which lead to
excessive growth of vines make them susceptible to certain foliar diseases, eg
powdery mildews.
Unfavourable conditions for disease.
– Most spores of fungi that cause leaf, flower and stem diseases need water to
germinate. Space plants and use drippers rather than misters, to reduce humidity
and discourage spore production and germination. Sprinkler irrigation increase
Sclerotinia and Pythium on peanuts.
– Fruit trees and vines can be trellised and pruned appropriately to provide aeration.
– Keep plant surfaces dry in greenhouses. Minimize duration of leaf wetness.
– Adjust temperature and humidity in greenhouses to minimize risk of grey mould
(Botrytis cinerea). The use of exhaust fans to circulate air in greenhouses reduces
dependence on fungicide sprays.
– Handle fruit and flowers gently during harvesting and packing to prevent bruising
which provide entry points for post harvest fungal diseases.
SANITATION.
Sanitation includes all activities aimed at reducing or eliminating the amount of
inoculum present on a plant, in a nursery, glasshouse or other situation to prevent the
spread of disease to healthy plants.
Destruction of diseased plant material.
– Many fungi overwinter on the shoots of host plants, pruning out infected parts is
essential for control, eg powdery mildew of apple.
– Damping-off fungi grow on dead seedlings and cuttings in propagation areas,
remove such materials promptly.
– Some fungi, eg brown rot of stone fruit, overwinter on fallen fruit; one of the
recommended sanitation procedures for the control of brown rot is to destroy all
fallen fruit as soon as possible.
– Tree surgery techniques are used to assist in control of wood rotting fungi.
– Produce rejected during harvest and packing should be removed and destroyed
each day to prevent the spread of spores by wind and water splash.
Cleaning and disinfecting surfaces in nurseries is important in the control of
soilborne and other diseases.
– Remove all dirt and organic matter (roots, sap, etc), from floors, benches, tools,
equipment, trays, pots, etc.
– Then thoroughly wash them all.
– Treat surfaces with a disinfectant at the concentration and for the recommended
time. Check that the disinfectant you want to use is effective against the problem you
have, eg Phytophthora. Use only freshly prepared disinfectant (used disinfectant
solutions may not work).and whether the surfaces are steel or plastic.
– Keep all all treated surfaces/objects in a clean area away from dirt and other
contamination until required.
Remember to treat water and media/potting mixes as necessary.
328 Fungal diseases - Integrated disease management