PLANT PROTECTION 1 â Pests, Diseases and Weeds

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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
PLANT PROTECTION 1 – Pests, Diseases and Weeds LIST OF SOME SPECIES Not known in Australia Limited distribution Not known in Australia Nematode-disease complexes Humans and animals COMMON NAME SCIENTIFIC NAME HOST RANGE (not exhaustive) Root knot nematodes Meloidogyne spp. Wide host range, more than 2000 plant species Root lesion nematodes Pratylenchus spp. Wide host range, cereals, fruit trees, roses, turf Celery eelworm Pratylenchus hamatus Celery and parsley in the USA, Stem and bulb nematodes Foliar nematodes (leaf nematodes) not known to occur in Australia Ditylenchus dipsaci Bulbs, phlox, oats, medics, clovers, Vicia faba D. myceliophagus Mushroom mycelium in Aphelenchoides ritzemabosi A. fragariae mushroom crops Chrysanthemum, Coleus, others Strawberry, anemone, kangaroo paw, others A. composticola Mushroom mycelium in mushroom crops Citrus nematode Tylenchulus semipenetrans Citrus, other Rutaceae, grapevines, olives, other plants Dagger nematode Xiphinema index Fig, grapevine, stone fruit, turf, may transmit plant viruses Cereal cyst nematode Potato cyst nematode (PCN) Stubby root nematodes Heterodera avenae Globodera rostochiensis Trichodorus spp. Paratrichodorus spp. Wheat, oat, barley, wild oats, barley grass, ryegrass, triticale. Important and damaging Potato, other Solanaceae, eg capsicum, eggplant, tomato, nightshade Fruit, vegetables, annuals, turf Mostly horticultural crop plants, turf, occasionally bush soils. May transmit plant viruses. Annuals, turf, etc Spiral nematodes Rotylenchus spp. Helicotylenchus spp. Pinewood wilt nematode Bursaphelenchus xylophilus Pines. Burrowing Radopholus spp. Banana, sugarcane, fruit, nematodes vegetables, weeds Beet nematode Heterodera schachtii Beets, some Brassica spp., radish, rhubarb, spinach, dock Nematode-bacterial disease complexes (page 253) Nematode-fungal disease complexes (page 253) Some nematodes are human and animal parasites, including: Hookworms in humans, dogs and cats. Heartworms in dogs. Filiariae in humans and animals. Threadworms, pinworms especially in children. Trichinae in humans from eating contaminated pig meat. Some strains of Paecilomyces lilacinus, a common fungus associated with Meloidogyne egg masses, has potential to be a threat to human health (Walker 2006). Indicators of soil conditions Nematodes as natural enemies Free-living, soil-dwelling nematodes are useful as indicators of soil conditions because of their high abundance, widespread occurrence and rapid response to change (Hodda et al 1999, Stirling et al 1999). Fungal-feeding nematodes are more abundant under conventional tillage. Bacterial-feeding nematodes are more abundant under direct drilling. Predatory nematodes Many genera Prey on plant parasitic nematodes in soil, possible commercial use Predatory nematodes Many genera Prey on plant parasitic fungi in soil, possible commercial use Saprophytic nematodes Many genera Feed on organic matter in the soil Nematode diseases 257
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Insect secretions PLANT PROTECTION
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Control methods Cultural methods.
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Root structure of dock (Rumex spp.)
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PLANT PROTECTION 1 â Pests, Diseases and Weeds