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Weed Management Guide Weed (Tribulus identification note Caltrop terrestris) Caltrop (Tribulus terrestris) Overview Caltrop is toxic to stock, causes injuries to humans and stock and can contaminate produce such as wool and fodder. Caltrop is declared under the Natural Resources Management Act 2004. It is prohibited to move or sell plants or goods carrying plants or plant parts. The landholder must control plants. Description Caltrop is a prostrate annual herb with stems spreading out for up to 2 metres from a woody taproot. Leaves consist of 4 to 8 pairs of opposite oblong leaflets. The upper surface is dark green, while the lower surface is covered with hairs, giving the surface a silvery appearance. Flowers are small, 8–15mm in diameter and bright yellow with 5 petals, usually lasting only one day. Caltrop flowers from spring to autumn. Images: Forest and Kim Starr Fruit consists of a woody burr with sharp, rigid spines, which splits into segments when ripe. Each segment has four hard spines; two spines are long and two shorter. Impacts Caltrop is toxic to stock and can cause nitrate poisoning, photosensitisation and staggers. Caltrop may also chemically inhibit the growth of other plants. Its spiny burrs can damage the feet of livestock and injure humans. They deter recreational activities due to the pain and injuries that can be caused when falling or treading on an infestation. Clean shoes, machinery and vehicles before moving out of areas of caltrop infestation. Burrs also contaminate produce such as fodder and wool. If you have land infested with caltrop, minimise movement in these areas. Distribution Caltrop is thought to have been accidentally introduced prior to 1896 as a contaminant of seed from the Mediterranean area, South Africa or California. It is most abundant on light sandy soils but will grow on almost any soil type region when there is adequate summer rainfall, high summer temperatures and sunlight intensity. Lifecycle Caltrop germinates after rainfall in late spring and summer as soil temperatures increase. There is a succession of germinations throughout summer following each rainfall event. Plant growth is rapid and a deep root system develops in a few weeks. With a low water requirement these plants survive prolonged dry conditions. The first flowers appear within three weeks and the first fruit within five to six weeks of germination. Flowering may continue for several months until early winter, when plants die. Fruit are produced continually throughout summer and autumn. More than 1000 seeds can be produced by a single plant and seed can remain viable for many years. Hygiene practices Preventing the spread of caltrop is the best control measure. Caltrop fruit are well equipped for dispersal: whichever way the fruit lies on the ground, one of the spines almost always points upwards. Fruit readily attach to the feet of animals, vehicle tyres, rubbersoled shoes and almost any object that is placed on it. Fruit also become embedded in sheep fleece. When this is not possible, make sure you remove any burrs to prevent further spread. What to do Competition Competition is a very effective control method for Caltrop as it is a poor competitor; it only achieves dominance when other vegetation is removed and ground is bare. Heavy mulching and healthy thick ground covering plants and grasses can suppress germination of caltrop. Chemical control There are a wide range of herbicides available for controlling Caltrop. Seek advice and further details from your local NRM Board office. When considering using chemical spraying as a control measure, it is important to remember that there is likely to be a succession of germinations of this weed throughout summer. Therefore, more than one spray application may be necessary, particularly if a residual chemical is not used. The timing of spray applications is critical to ensure that the majority of the weeds have been sprayed before seed set occurs. Using spraying as the only control method can be impractical and it is usually better to combine spraying with other means of control. Manual removal Hand-pulling Caltrop is effective if the infested area is not too large. This method might also be more appropriate in environmentally sensitive areas. The key is to pull from the root crown, where the weed spreads from, in order to remove the tap root. Please contact your local Board office for further information, advice and assistance in controlling Caltrop Adelaide and Mount Lofty Ranges Natural Resources Management Board contacts Eastwood – T: 8273 9100 Gawler – T: 8523 7700 Lobethal – T: 8389 5900 Willunga – T: 8550 3400 [email protected] www.amlrnrm.sa.gov.au May 2012 Acknowledgements: This factsheet has been adapted from the original produced by the Northern and Yorke Natural Resources Management Board.