PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
CONTROL
METHODS
Control methods aim to maintain pest populations at acceptable levels. It is
hard to quantify some of the non-chemical controls. Expense and type of crop
being grown, limit the actual method employed.
LEGISLATION, STANDARDS, ETC
These include Plant Quarantine Acts, Seed Acts. Pesticides Acts, Organic Standards.
CULTURAL METHODS.
Cultural practices that promote root growth will enhance tolerance to nematodes.
Crop rotation is difficult as many nematodes have a wide host range. However,
effective rotations, where practical, are an essential part of nematode management.
During fallowing, soil is cultivated once a week and after each period of rain.
Nematode eggs hatch during the fallow but without food plants the larvae die. The
area is kept free of weeds and other plants (possible hosts for the nematodes), for
one whole season. Today fallowing is regarded as environmentally unsound.
Soils rich in organic matter support high populations of predatory fungi and
nematodes which feed on plant parasitic nematodes. Although effective, large
quantities of compost are not practical for large areas.
Conservation tillage (CT) is considered to promote large numbers of microbial
competitors or antagonists of soilborne disease organisms.
Avoid overhead irrigation which spreads foliar and other nematodes which
attack the above ground parts of susceptible plants, if nematodes are present.
Toxic secretions of some plants are reputed to diffuse into the surrounding soil
and kill some species of nematodes (page 270).
Some crops, starting from transplants, may be more tolerant of nematodes
than direct-seeded crops.
SANITATION.
Maintain good general hygiene. Keep floors and benches clean of plant
debris to prevent cross infection. Wash infested soil from boots, containers, tools
and machinery to prevent spread of nematodes to clean areas.
Prune out and destroy plant parts infested with foliar nematodes. Remove
badly infected plants. Dig up, together with a spadeful of the surrounding soil,
infested bulbs and other infected root parts. This is only suitable for small areas.
Burn or destroy by some other means nematode-infested plant material. Do not
placed on compost heaps or feed to stock.
Use wire mesh bench tops to support containers, preventing nematodes
swimming in drainage water from infested pots to uninfested pots.
Do not use recycled potting media unless it has been adequately treated.
Suppressive soils
are soils in which certain
diseases are suppressed
because of the presence
in the soil of microorganisms
antagonistic
to the pathogen.
BIOLOGICAL CONTROL.
A bacterium, BioNem (Bacillus firmus), a naturally occurring soil bacterium, is
used overseas as a seed treatment to reduce nematode populations and root
infestations in soil while stimulating increased yield in vegetables, stone fruit, herbs
and flowers. Another bacterium, Pasteuria (Bacillus) penetrans) parasitizes some
species of root knot nematodes.
A fungus, Paecilomyces lilacinus is being researched in Australia for biocontrol of
root knot and cyst nematodes (Holland and Williams 1998). P. lilacinus is primarily
an egg parasite, hyphae grow on the egg surface prior to invading it. Other fungi
being researched include Dactylella oviparasitica (an egg parasite) and some
mycorrhizal fungi, eg Gugaspora, Glomus.
Trap plants are sometimes considered to be a form of biological control. Root
knot nematodes enter roots of the French marigold (Tagetes patula), but cannot
complete their life cycle (page 270). A thick cover of marigolds is needed, the
marigolds are turned in at end of the season.
Bacterial and fungal endophytes for the biological control of plant parasitic
nematodes, eg root knot (Meloidogyne incognita), are being researched for tomato,
potato and turf. Endophytic fungi may suppress plant parasitic nematiodes.
Suppressive soils. There is a range of natural enemies, eg predatory nematodes,
nematode-trapping fungi, parasitic bacteria and fungi, in the soil which assist in
controlling plant parasitic nematodes. These organisms could be genetically
engineered or enhanced and agronomic practices adopted to improve the physical,
chemical and biological properties of soil. This would improve the suppressive
nature of the soil and the capacity of plants to withstand nematode attack.
Bio-stimulants (derived from plant extracts and fatty acids) reduce the feeding
vigour of plant parasitic nematodes, stimulate certain predatory nematode species
and improve a plant’s ability to tolerate many pathogens and environmental stresses.
– DiTera ® (a natural product from the hyphomycete fungus Myrothecium spp.,
composed primarily of proteins, sugars, and lipids) effectively kills plant parasitic
nematodes in the soil by contact.
– Furfural (an industrial chemical derived from a variety of agricultural by-products,
eg sugarcane bagasse, corn cobs, oat and wheat bran, sawdust).
– Agri-Terra ® (colloidal suspension of potassium mono-phosphate, polysaccharides
and surfactants) smothers some species of nematodes and disorientates others,
causing them to loose the ability to parasitize plant roots and reproduce.
– Sincocin, Agrispon contain extracts from plants (sesame, wintergreen, citrus oils,
neem, Brassica meal and mustard bran).
Nematode diseases 263