PLANT PROTECTION 1 â Pests, Diseases and Weeds

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PLANT POTECTION 1 – Pests, Diseases and Weeds Management (IDM) 1.Planning. Soilborne diseases generally are widespread and like other diseases, their control requires appropriate planning and management. Most states and territories have management plans for Phytophthora to reduce its impact and prevent further spread. Select a program for managing Phytophthora for your situation, eg Biodiversity conservation in forests, bush areas, etc (Management of Phytophthora cinnamomi for Biodiversity Conservation in Australia) www.cpsm.murdoch.edu.au/ Nursery Industry Accreditation Scheme Australia (NIASA) is a national scheme for production nursery (growers) and growing-media (potting mix) supplier businesses. Australian Garden Centre Accreditation Scheme. Cutflowers (Phytophthora diseases of cutflower crops). Key Avocado Management Issues. Most states provide information on Phytophthora management in their region or on certain crops. Management plans are available for many other soilborne diseases, eg Total Crop Management - Clubroot (of Brassicas), Management of Soilborne Diseases in Vegetable crops (Biological Crop Protection www.biolcrop.com.au/ ). Horseriders, bushwalkers, landcare groups. 2.Crop, region. The wide host range of Pc in many regions means that you must know your crop history and susceptibility, and your local climatic variations favouring Pc. 3.Identification by laboratory analysis is essential to ensure effective control and prevent spread (page xiv). Pre-plant soil tests can now be carried out months prior to planting. Any water supplies in contact with the ground must be suspect, eg dams, streams, soaks must be tested. 4.Monitor symptoms and, hygiene procedures and chain of production. Also monitor for the presence of Phytophthora in water, soil, roots and other plant material. Record all results. Remember know when, where, what and how to monitor. Symptoms. First look at plants closely for evidence of wilting. Examine indicator plants in bush areas, eg grass trees (Xanthorrheae sp.). Assess root health of potted plants, eg closely examine the collar region and cut into the internal tissue with a knife to detect evidence of infection, also wash potting mix/soil from roots and examine them under a dissecting microscope against a white background, comparing them with a known specimen of healthy root material. If diseased, seek expert testing, as there is increased detection of new Phytophthora spp. 5.Threshold. This will be determined by relevant regulations. Beyond that you will have to decide your own economic, aesthetic or environmental threshold. 6.Action. Take appropriate action when any threshold is reached. In practice, this usually includes cultural methods, sanitation (hygiene), quarantine, use of tolerant rootstock, Pc-free planting material and media and the application of fungicides. 7.Evaluation. Review the program, compare methods and results with previous years. Make improvements if needed, eg ensure planting material is disease-tested, varieties have some resistance, improve culture and sanitation, preplant soil treatments, eg solarization, bio fumigants, water treatments, etc. Control methods Control of root diseases is difficult both in the field and in intensive crop production systems - there is often a combination of ‘causes’ and therefore a combination of control methods are required. Methods used depends on the situation, eg forest, bushland, cutflowers, nurseries, hydroponic systems, containers, soil/media, water sources, etc. The aim being not only to control disease on current crops but also prevent further spread. It is difficult to eradicate Phytophthora and other soil diseases from an infested site especially when perennial crops are grown. LEGISLATION, REGULATIONS. The Commonwealth‘s Environment Protection and Biodiversity Conservation Act 1999 seeks to promote the recovery of species and ecological communities that are endangered or vulnerable and to prevent other species and ecological communities from becoming endangered. An off shoot of this law is: A Threat Abatement Plan enables a national management approach for Dieback caused by the root-rot fungus (Pc). Lists of threatened species and ecological communities have been prepared. Some states have developed priorities and coordinate management to limit spread of Pc into area which is Pc-free. Certification schemes for the production of Pc –tested planting material and media. Cultural methods. Large scale remediation can protect rare taxa and communities of high conservation value threatened by nearby Pc infestations. It may involve long term in situ seed conservation and prioritization of certain species. Select sites unfavourable to Pc and avoid conditions favouring disease (page 365). Prepare soil appropriately. Grow plants in soilless media or hydroponics. Suppressive compost and mulches are suitable only for small areas. Marri, karri and other hardwood bark can be highly suppressive of Phytophthora after composting. It suppresses weeds and aids soil moisture retention during summer. Take care not to import contamination. Add organic manures. Maintain crop vigour. Plant when temperatures are favourable for crop growth, not Pc. Seek advice regarding nutrient requirements for your crop. Irrigation and drainage – Design, maintain and monitor irrigation systems to avoid overwatering throughout the year and minimize the time soil is saturated. In infected blocks of trees, adjust irrigation to suit smaller trees. In greenhouses reduce excess water lying in bays. – Sub-irrigation may result in spread of motile zoospores from infected to healthy plant. – Most serious problem associated with zero runoff involves Pc. Regulations require zero run-off for some nursery growers resulting in rapid change to closed systems of production. – Use free-draining potting mixes and avoid overwatering. Improve surface and sub-soil drainage in poorly drained sites by various means including planting into raised beds. – Avoid exposure of susceptible trunks to infection, eg avoid irrigation spray directly contacting trunks. – Maintain plantings under sod rather then bare soil; keep areas at base of trees free from weeds. Surface water management and drying of sites. – Avoid ‘balling roots’ in old potting mix during repotting (page 367). – Compacted soil could be ripped, mounded beds. Crop rotation and fallowing. – Avoid continuous cropping with susceptible hosts. – Where different species are being planted undertake risk assessment. – When replanting understand ‘sick soil syndrome’. – Consider including a bio-fumigation crop in a rotation (page 267). Green manure cropping reduces soil crusting, improves filtration, increases soil organic matter and reduces subsoil compaction. Brassica green manure crops produce high concentrations of bio-fumigants and may improve soilborne disease management. The native legume (Acacia pulchella) protects Banksia grandis from infection, suppressing the fungus in the soil. Reduced tillage. – Can encourage some soilborne diseases, eg Fusarium graminearum, F. culmorum, F. avenaceum of wheat and Cephalosporium gramineum, Pythium and Rhizoctonia. Crop residues can maintain the inoculum of these fungi while fields are left fallow or sown with a non-host break crop. – However, long periods (10 years or more growing seasons) of stubble retention can induce disease suppression of pathogens such as Rhizoctonia. The induced disease suppression is thought to be due to the proliferation of indigenous micro-organisms in the soil, some of which are antibiotic and antifungal that prevent the outbreak of pathogenic fungi. 368 Fungal diseases - Examples of fungal diseases
PLANT PROTECTION 1 – Pests, Diseases and Weeds Sanitation. Hygiene As fungicides often only suppress and do not eradicate Phytophthora, they are not a substitute for good hygiene and cultural practice. Maintain cleanliness in propagation and growing-on areas in accordance with measures prescribed by prevent Nursery Accreditation Schemes. Avoid spread of disease by: Destroying all diseased nursery stock, etc. – Either using soil-free media or treat all soil routinely either by pasteurization or other means. – Foot baths of Biogram at the entrances to clean nursery areas and glasshouses and moving from unsurfaced to surfaced areas. – Cleaning, and then sterilizing footwear, tools, containers, machinery, vehicles, and trolleys using proven procedures, before entering an area (page 343). – Disturbing soil as little as possible in the bush. Always walk or drive on roads, if involved in off-road activities then clean shoes, camping equipment, tent pegs, etc. Weeders should work in areas free of the pathogen before working in areas known to be infected. Minimize activity when soil is very wet, put weeds in bags for removal from the site. Biological control. Natural controls. Many antagonists occur naturally in soils. – Fungal-feeding insects and mites, eg mites, springtails, protozoans, free-living nematodes and earthworms in soil, feed on fungal organisms and may contribute to their biological suppression. – The role of mycorrhizae in controlling Pc infection is not yet clear but on some hosts, eg Nothofagus in NZ lack of mycorrhizae may prevent establishment of seedlings. – Mechanisms by which antagonistic microorganisms effect pathogen populations are not always clear but are generally attributed to one of the following effects: 1. Direct parasitism (penetrating host hyphae) and killing them. 2. Competition with the pathogen for food. 3. Direct toxic effects on the pathogen by antibiotics substances released by the antagonist. 4. Indirect toxic effects on the pathogen by volatile substances, such as ethylene, released by the metabolic activities of the antagonist. – Suppressive soils with high organic matter content support antagonistic micro-organisms (mostly bacterial, other fungi and actinomycetes) which generally suppress soilborne diseases including Pc. Suppressive soils may also involve non-living factors and may vary with the disease organism and the crop. In most cases there are one or more micro-organism antagonists. They do not allow the disease organisms to reach high enough populations to cause severe disease. Biocontrol agents for certain seed and soil-borne plant diseases. Effectiveness of antagonistic micro-organisms can be increased by: – Introducing new or larger populations of fungal or bacterial antagonists, eg Fungal biocontrol agents based on Trichoderma harzianum, Clonostachys rosea and Coniothyrium minitans. C. rosea is near commercialization and has been proved effective in several crops against certain seed and soilborne diseases. Other fungi include Gleocladium, Coniothryium, Myrothedium. Candida. Trials of Trichoderma on Phytophthora seem to be variable, ie mycelium may be suppressed but oospore production stimulated. Bacterial biocontrol agents based on Bacillus, Agrobacteriaum, Pseudomonas and Streptomyces. Paenibacillus polymyxa. Also Burkholdia. The use of several bio-control agents at once may reduce the effects of root rot disease complexes. – Adding soil amendments that serve as nutrients for, or otherwise stimulate growth of the antagonists and increase their inhibiting effects on disease organisms. However, these organisms cannot maintain themselves very long and organic amendments are not selective enough to select and buildup up populations of the introduced or existing antagonists. Chitin in fertilizer is thought to stimulate antagonistic fungi in soil. Commercially available bio-control agents. There is an increasing number being marketed (page 344, Table 60). These include: – Trichoderma harzianum suppresses many soilborne fungal diseases, eg for Fusarium, Phytophthora, Pythium and Rhizoctonia. – Bacillus subtilis as a plant growth promoting, bio-balancing agent, eg for Pythium, Fusarium, Rhizoctonia and Phytophthora. – Mixtures of antagonists. There is often a combination of causes (several root rotting fungi, nematodes, etc) so it is logical that several antagonists or suppressive agents may be more successful than one. Nutri-Life TrichoShield TM (Trichoderma spp., Gliocladium virens, Bacillus subtilis) for seed, seedlings, transplants, bulbs, cuttings, grafts and established crops. Noculate Liquid (Bacillus, Trichoderma, vitamins, humic acid, kelp) is used on professionally maintained turf. Fulzyme Plus (B. subtilis + amino acids) may suppress Phytophthora and Pythium in certain situations. – Biofumigation. Fumafert (mustard seed meal (Brassica juncea) and neem kernel (Azadirachtin indica)) is a soil amendment with biofumigant properties which may aid in the control of certain soilborne insects, diseases and nematodes. Resistant/tolerant varieties. Although there is a continual development of resistant varieties, little is known about resistance or tolerance to soilborne diseases. Genetic resistance to root diseases is arguably, uncommon. Younger plants may be more susceptible than older plants. . Address issues by: Increasing the density of tolerant native species. Plant tolerant cultivars or species when available. Obtain information from relevant authorities. Systemic acquired resistance (SAR) stimulates the natural SAR response mechanisms found in most plant species. Bion Plant Activator Seed Treatment (acibenzolar-s-methyl) suppresses certain soilborne diseases, eg Fusarium wilt and black root rot of cotton in IDM programs (page 329). GE crops have been developed with resistance to some soilborne diseases, eg cotton has been genetically engineered to be resistant to Verticillium wilt a major disease of that crop. Resistant rootstocks are useful for some crops, eg avocado, macadamia, pineapple. – Seedling and M9 rootstocks of apple appear to be most resistant to Pc, others are very or moderately susceptible to Pc. – Tomatoes may be grafted onto rootstocks with some resistance to root knot nematodes, Verticillium and Fusarium wilts. – The Phytophthora-resistant Westringia fructicosa has been found to be compatible with over 40 Prostanthera spp. Replacement crops have been investigated for the jarrah forest area of WA, and it is now known which groups of eucalypts are most susceptible to Pc. Lists of native plants which are tolerant or highly susceptible, under some conditions are available (Phytophthora Science and Management). www.cpsm.murdoch.edu.au/ Plant quarantine. The following notice is not uncommon in some areas: PROHIBITED AREA NO ACCESS BEYOND THIS POINT Phytophthora Infested Area Fungal diseases - Examples of fungal diseases 369
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Root structure of dock (Rumex spp.)
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PLANT PROTECTION 1 â Pests, Diseases and Weeds