PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
CLASSIFICATION
IDENTIFICATION,
SAMPLING
Symptoms
Soil
Plant material
Indicator plant
All plant parasitic nematodes belong to the Phylum Nematoda. There are several
orders, sub-orders and families into which they are classified mainly according to their
morphology, eg
Presence or absence of stylet, size and structure of the style itself.
Position of the oesophageal glands.
Structure of the female reproductive system, number of annules in the lip region.
Tail shape can be used to identify nematodes at a species level.
Also occasionally, the plant organ attacked, symptoms and mode of parasitism.
VISUAL EXTERNAL SYMPTOMS.
Below ground symptoms can be quite distinctive, eg root knot on carrots, but
they do not indicate which species of root knot nematode. Also, root knot galls
could be confused with nitrogen-fixing nodules on some hosts.
Foliage symptoms.
– Foliage nematodes. Similar symptoms can be caused by various non-parasitic
agencies, so get to know your crop.
– Root nematodes. The presence of nematodes can be suspected if crops/turf lack
vigour and do not respond to fungicides, irrigation or fertilizers.
MORPHOLOGY/MICROSCOPY.
Simple nematodes can be seen with a dissecting microscope (x 10).
Not all nematodes seen under microscope are pests, eg on rotting bulbs,
saprophytic nematodes may be feeding on and biodegrading organic matter.
Various keys based on morphology have been developed to help identify plantparasitic
nematodes but identification to species requires a specialist
nematologist in a diagnostic laboratory. Sometimes nematodes cannot be
identified using morphological features alone.
While tools such as DNA bar-coding may provide rapid identification, studies of all
nematodes in soils must embrace their morphology, biology, soil structure and
moisture, available nutrients, microbial populations, ecological relationships, eg
pathogenicity to plants, invertebrates, etc.
NEMATODE DIAGNOSTIC SERVICES provide information on:
Sampling and/or extraction procedures.
Handling and storage of samples prior to dispatch.
Planning IDM programs.
IDENTIFICATION BY SPECIALISTS.
Soil and plant analysis.
– Soil sampling. Obtain information from the diagnostic laboratory on when and how
to collect samples and dispatch them. Generally, collect soil samples before planting,
store at 10-15 o C until dispatch. They will extract, identify and count nematodes
present and interpret results. Traditional extraction techniques may fail if populations
are low or in the dormant stage.
– Plant material, eg roots, leaves (above ground parts).
Bio-assays.
– Variations in host range can occur within a species and these can only be
detected by testing the nematode against a range of plant species.
– Indicator plants. In root knot nematodes the juvenile is the only stage found in the
soil. Since all species have morphologically similar juveniles a bioassay on selected
indicator plants may be used to distinguish species.
– Detecting low populations of root knot nematodes. Susceptible plants, eg
tomato seedlings, are grown in soil samples for about 1 month and then the root
system is removed and examined for galls. Their occurrence indicates the presence
of root knot nematodes. Large samples can be processed, also eggs in soil can hatch
and infect the plant. Samples must be collected at least 1 month before planting.
– A nematode count is the only way to quantify their presence and determine whether
the numbers present will be detrimental to plant health.
Other diagnostic tools.
– Rapid and reliable diagnostic procedures for major pest nematodes are
continually being developed; including computer based analytical tools and DNA
technologies for identifying and quantifying nematodes.
– Field tests are being researched using immunochemical devices to identify
nematode species, eg Anguina tritici, A. funesta, Meloidogyne javanica.
– Molecular assays for soil-borne pathogens in cropping soils PreDICTA B by
SARDI, eg pathogenic oomycetes, fungi and nematodes, beneficial fungi.
– Keys, eg Plant Parasitic Nematodes (Lucid key) www.lucidcentral.org/
Key to the Nematodes of Australia www.ento.csiro.au/science/nematode.html
– Nepo viruses are transmitted by nematodes and a generic test is being developed
for the whole nepovirus group.
Routine DNA-based testing service for soilborne diseases in Australia so
that likely losses can be predicted well before the crop is planted. Growers can
change cultivars, crops, modify cropping programs where risk of crop loss is high.
Many soil pests and diseases can be identified from a single soil sample.
Training programs are available so that results of testing can interpreted
accurately at the farm level.
256 Nematode diseases