PLANT PROTECTION 1 â Pests, Diseases and Weeds

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PLANT PROTECTION 1 – Pests, Diseases and Weeds CULTURAL METHODS (contd) MULCHES. Suppress annual weeds by excluding light needed for growth. Are not very effective against perennial weeds, eg tap rooted dandelion, stolons of couch grass. Nutgrass may grow through polythene film < 0.2 mm thick. Weed mat may be laid beneath mulches to prevent roots of perennial weeds which do develop in the mulch, from penetrating deep into the soil, making removal easier. Must be porous to allow water to seep through and air to circulate, of the correct depth, and aged and/or composted before use. Preferably lay when soil is moist. Before applying mulch, remove or spot spray weeds, especially perennials weeds. Mulches protect soil from wind and sun, reducing losses from evaporation. – Reduces soil temperature fluctuation, eg by up to 5 o C in summer, in winter mulches shade soil from spring sunshine, slowing spring crop growth. – Protect surface and shallow feeder roots, increase beneficial soil microbes. – Coarse mulches control windblown weed seeds better than fine mulches. – Provide cleaner and easier harvesting of strawberries and ginger roots, etc. Mulches may be: – Inorganic, eg woven plastic weed mats, blue metal, crushed brick, river gravel mostly need to be applied to a depth of 9-10 cm to provide adequate weed control. – Organic, eg bark, wood chips, sawdust, straw, hay, compost, pine needles, leaf litter. Pre-cut disks of breathable durable recyclable polypropylene can be placed around new or existing tress and shrubs, posts and in planters. Paper (pellets, sheets, rolls), cardboard, seaweed, wool, etc. – Mulches provide shelter for termites, slaters, etc. They can be a fire hazard. SANITATION , . CAREFUL MANAGEMENT. Sanitation may overlap with Physical and Mechanical Methods (page 438). Sanitation is important at all levels of quarantine to prevent spread of weeds, eg washdown facilities in the NT for barges going to the Tiwi Islands. Cleaning mowers, slashers, vehicles and earthmoving equipment after use in weedy areas before using in clean areas to reduce spread of weeds such as Chilean needlegrass. Suppress weeds by persistently preventing seed set and spread when weed populations are low as well as suppressing outbreaks of new weeds as soon as they occur by cultivation, mowing or herbicides, etc. For greenhouses maintaining a 3–6 meter weed-free barrier outside the greenhouse helps to minimize weed seeds entering via vents and doors. – Screening vents prevent windblown seeds. Porous concrete walkways and geotextile fibre mats under benches help prevent establishment of weeds. – Keep potting mixes and ingredients covered. – Pots may be isolated from direct soil contact by use of screenings (8–10 cm of 18–20 mm gravel or blue metal) and concrete paths. – Nursery accreditation schemes specify weed control measures. Disposal of garden waste, weeds. – There are still many species in gardens that could naturalize in Australia. – Do not dump garden waste in bushland, over fences or cliffs or into creeks. – Recycle waste through local council or take it to the local tip. – Cover trailers when taking garden waste to the tip so seeds and cuttings do not fall off and invade roadside bushland. Double bag garden waste (place in one bag, knot, then place in another bag to stop seeds being spread en route, compost garden waste at home or take to a recycling site. – Composting garden waste at 60 o C for 30 minutes will not kill most weed seeds. Properly carried out composting of bark will kill most weed seeds and plant parts. Hand pulling and digging out annual or herbaceous perennial weeds before they set seed, is suited for small shallow rooted weeds and small infestations. Easiest when soil is soft and moist. A mattock is useful for digging out many weed species. Hand weeding is laborious and can be an ineffective means of selectively removing weeds in large areas. Remember the soil disturbance will move more weed seeds into the germination zone. Cutting woody weeds. Use secateurs, hand saw or chainsaw is often used for controlling woody weeds and for some species that do not re-shoot, can be done without need for herbicides, eg wattles, pines (pages 467-468). Control weeds on non-crop areas around the nursery, farm, etc before they set seed. Immediate removal of undesirable weeds or strategic spot spraying can halt spread of weeds and reduce or eliminate use of herbicides. Prevent spread especially when moving soil and plant material through the landscape. Some systems allow for the collection of weed seeds at harvest. 434 Weeds - Integrated Weed Management
PLANT PROTECTION 1 – Pests, Diseases and Weeds BIOLOGICAL CONTROL Also called microbial agents Mycoherbicides require a moist environment CLASSICAL BIOLOGICAL CONTROL. is the deliberate release of a pest or disease after careful screening, to control a particular weed. Successful biological control is the most effective way to control most weeds in the long term. Weeds targeted for biological control are listed on the website below: Target species for biological control www.weeds.org.au/target.htm Biological Control Act 1984 (Cwlth) provides for the control of persons releasing agents, choice and declaration of target organisms and biological control agents, and approval for release. The introduction of a potential biological control agent is separately assessed under the Quarantine Act 1908 and the Environment Protection and Biodiversity Conservation Act 1999. The assessment involves comprehensive host testing (testing what plants the biological control agent will attack) before release. Releases of biological control agents are made by a range of organizations, eg – Division of Entomology, CSIRO, Canberra. – Cooperative Research Centre for Weeds Management Systems. – Various task forces, eg NSW Lantana Biological Taskforce. – State Departments, eg Qld Dept. of Natural Resources. – Private companies. Self-sustaining. Classical control offers the only possibility for controlling many environmental weeds. Once established the pest or disease can spread naturally and reach long term equilibrium with its weed host, eg – Prickly pear by caterpillars of the Cactoblastis moth. – Skeleton weed by several insects and mites, and a rust disease. – Paterson’s curse by several beetles and a leafmining moth. – Blackberry by a rust disease. – Bitou bush by various insects and a rust disease. Bitou bush is rated as the worst pest plant in the Australian coastal environment. Control has been hampered by drought during which leaves lose nutritional value making it difficult for young larvae to get a niche among the growth tips (Tortrix leafrollers) but other biological control agents such as the bitou tip moth (Comostolopsis germana) and the seed fly (Mesoclanis polana) are doing better. – St John’s wort by a leaf beetle, various other insects and a rust disease. – Giant sensitive plant (Mimosa pigra) by more than 5 biocontrol agents. – Bellyache bush (Jatropha gossypifolia) by insects in Qld. – Bridal creeper by the bridal creeper leafhopper (Zygina spp.). – Salvinia by a weevil (Cyrtobagous salviniae). – Parkinsonia seed pods are eaten by camels reducing the plants ability to reproduce. – Lucid Keys Identification Tool for Weevil Biological Control Agents of Aquatic and Terrestrial Weeds in the United States and Canada. BY BIO-HERBICIDES. (mostly myco-herbicides) Bio-herbicides are fungi, bacteria and other microorganisms, applied as a spray to weeds, causing an immediate epidemic resulting in death or reduced vigour. Effects tend to be short term in much the same way as chemical herbicides, eg – Overseas a fungus (Ascochyta caulina) can kill the main weeds affecting 10 major crops in Europe. It must be applied early otherwise weeds outgrow the fungus. It will not be available commercially for many years. Mycoherbicides including a fungus (Phytophthora spp.), are being researched to control the strangler weed in citrus orchards in Florida. – In Australia, Colletotrichum orbicular is being researched to control Bathurst burr (Xanthium spinosum) and Drechslera avenacea to control wild oats. Main constraint to the development of commercial mycoherbicides is the requirement of fungi for high moisture or free water environment. Formulations have been developed to overcome these constraints. Contraceptive sprays. Self-incompatibility (SI) is a biological system that prevents certain plants from fertilising themselves with their own pollen thus reducing the production of fertile seed. Research is proposed to apply non-toxic sprays that mimic chemicals produced by certain plants to prevent self fertilization, allowing the plant to detect and ignore its own pollen. Wild radish (Raphanus raphanistrum) is one of the weeds to be trialled. Allelopathy is a release of a chemical by one plant species into the environment, which interferes with weed seed germination and growth of surrounding plants. – Massive reductions of fat hen has occurred in sunflower crops, sown no-till into desiccated green rye cover crops. – However the use of white mustard green manure (Sinapis alba) to control weeds in spinach and pea was more toxic to these crops than to weeds. – Several rice strains that apparently exude a chemical keep weeds at bay. www.regional.org.au/au/allelopathy/2005/2/1/index.htm Weeds - Integrated Weed Management 435
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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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