PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
CONTROL
METHODS
(contd)
Biocontrol agents
can be affected by
fungicides and
environmental factors
such as moisture
and temperature
Vegetatively propagated
plants have greater
uniformity. Severity of
disease outbreaks
increase as genetic
uniformity of the host
crop increases.
Blights/Cankers
In SE Asia, leaf blight
(Kirramyces destructans)
and stem cankers
(K. zuluensis) causes
diseases of eucalypts
and may have spread
around the region on
infected germplasm.
These diseases could ,
endemic eucalypts and
the productivity of
commercial plantations
BIOLOGICAL CONTROL.
Antagonistic fungi and bacteria are naturally present in crop soils and exert
some control over fungal disease organisms. They do this by either by parasitizing
disease organisms, competing for food or producing antibiotic or volatile substances
such as ethylene. Some have been commercialized (page 344, Table 60).
– In suppressive soils, antagonistic microorganisms (mostly bacterial, fungi and
actinomycetes) suppress soilborne diseases. Most beneficial effects of compost
are due to the activities of antagonistic microorganisms.
– Trichopel , others (Trichoderma spp.) suppress soilborne fungal diseases
including Fusarium, Phytophthora, Pythium and Rhizoctonia.
– Companion (Bacillus subtilis) as a soil drench suppresses Fusarium, Pythum,
Phytophthora, Rhizoctonia, in protected environments. Fulzyme Plus (B. subtilis +
amino acids) may suppress Phytophthora and Pythium in certain situations.
– Nutri-Life TrichoShield TM (B. subtilis, Trichoderma spp., Gliocladium virens) for
seed, seedlings, transplants, bulbs, cuttings, grafts and established crops.
Mycorrhizal fungi belong to all fungal groups and are essential for establishment
and growth of many plant species. Plants with mycorrhizal roots can exploit a much
greater volume of soil than non-mycorrhizal plants. Mycorrhiza activators, eg
Mycorrcin, boost indigenous mycorrhizal populations increasing root colonization.
Endophytes (fungi or bacteria growing systemically in living plants), cause few or
no symptoms, but protects them from diseases and pests, while improving growth
and drought tolerance. The best known are probably the grass endophytes.
Hyperparasites. A fungus (Ampelomyces quisqualis) is a hyperasite of powdery
mildew (natural control).
Fungal-feeding insects and mites. Mites, springtails, protozoans, free-living
nematodes and earthworms in soil feed on parasitic fungi and may assist their
suppression. Up to 150 fungal-feeding mites can be found on some leaves. Some
beneficial ladybirds may eat powdery mildew fungi.
Others, eg a plant protein (finotin) has been extracted from the tropical forage
legume Clitoria ternatea and found to have broad bio-pesticide properties against
insect pests, a range of fungi and some bacterial disease organisms. A biofungicide
extracted from Swinglea glutinosa against powdery mildew on beans and
roses is currently marketed to flower growers overseas.
RESISTANT, TOLERANT VARIETIES.
For many fungal diseases, eg rusts, this is the only practical method of control.
Provenances of Eucalyptus nitens vary in resistance to Mycosphaerella leaf spot
(Mycosphaerella nubilosa).
Rootstocks. Susceptible tomato scions are grafted onto tomato rootstocks with
some resistance to Verticillium and Fusarium wilt diseases.
Traditional cross-breeding has been successful for centuries in producing
hybrids with a mix of characteristics. Interspecific crosses can be used to transfer
genes from one species to another closely related species.
Genetic engineering (GE) allows for quick transfer of individual genes or
combination of genes for resistance into susceptible crop varieties, reducing the time
required to develop new resistant varieties. Rust resistant genes in flax and maize
may be transferred into wheat.
Cross protection (mild strain protection). Dutch elm disease (DED)
(Ophiostoma ulmi) is carried from tree to tree overseas by the elm bark beetle
(Scolytus multistriatus). Trees possibly could be protected from DED by inoculating
them every year with a mild strain of DED.
Systemic acquired resistance (SAR). Plant activators stimulate the natural
SAR response mechanisms found in most plant species, to certain virus, bacterial and
fungal diseases and increase crop yield. They have no direct effect against the target
pathogens. Downy and powdery mildews, postharvest diseases and bacterial leaf
spots of certain vegetables are being researched. Bion Plant Activator Seed
Treatment (acibenzolar-s-methyl) suppresses Fusarium wilt and black root rot of
cotton in IDM programs.
PLANT QUARANTINE.
Quarantine treatments can prevent introduction or establishment of a disease
into an area, eg fumigation, hot water, fungicides, seed fungicidal dust, etc.
Australian Quarantine & Inspection Service. Many fungal diseases are
not as yet in Australia, eg many rust diseases, strains of brown rot of stone fruits.
Target list of diseases www.daff.gov.au/aqis/quarantine/naqs/target-lists
PaDIL - Pests and Diseases Image Library www.padil.gov,au
Interstate and Regional Plant Quarantine. Many fungal diseases already in
Australia have a restricted distribution, eg black spot of apple does not occur in
WA. Area/property freedom certification certifies that an area or property is free
from a specified disease, eg WA will accept gladioli from an area in Qld which is
certified to be free from gladiolus rust (Uromyces transversalis).
Local quarantine. Protocols have been developed for production nurseries to
prevent contaminated seed, plants and soil being brought into a nursery and to
prevent contaminated plants, soil, etc being supplied to growers, landscapers, fruit
growers, vegetable growers, cut flower producers, etc (BioSecure HACCP).
Fungal diseases - Integrated disease management 329