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Halting the invasion

Managing weeds has been an issue for agricultural producers for centuries; consequently there are now a wide variety of techniques used for managing and controlling weeds in an agricultural situation. But in order to successfully control or eliminate any weed farmers need to know which is the most effective and appropriate method, and in order to identify the most appropriate method agricultural scientists and researchers try to understand each plant’s ecology and lifecycle, so that relevant advice and support can be provided to farmers.

Whilst any and all of the various different types of weed can cause significant damage, and most will require careful management techniques to control, one specific type of weed – an invasive weed, can have devastating effects. An invasive species of weed is one which can be non-indigenous or natural to the local environment, but has a tendency to crowd out other plants or crops. This disruption can affect the local ecosystem significantly and cause economic implications and loss to farmers who find themselves over run by invasive weeds.

And yet there is only a limited amount of information on the population dynamics and ecology for invasive plants, and the same is true for the associated soil seed bank ecology or seed persistence: hence it has been difficult to formulate well planned strategies for the management or elimination of invasive weeds. The soil seed bank ecology and seed persistence of one particular species of invasive plant however has recently been studied by Australian researchers at the Alan Fletcher Research Station in Queensland. Lantana camara is now considered one of the most invasive species of weed in tropical and subtropical areas, and has been labelled as a Weed of National Significance in Australia, hence the researchers chose to try and understand the factors affecting seed survival and seedling emergence. Historically it has been a difficult weed to manage through biological measures or through introduction of specific pests to control its spread. Additionally as its seeds are bird-dispersed it is difficult to manage through the removal of seed sources, given the sources can be wide ranging. So one possible method of controlling or eliminating Lantana camara is through depleting its soil seed bank, and in order to do this a deeper understanding of the Lantana’s seed germination and survival is needed.

A detailed study was carried out over a number of years in Queensland using controlled sites with artificial irrigation and more natural sites using rainfall for watering. Information was taken on seed size, germination responses including monitoring the depth the seed was planted and the climatic conditions, seedling emergence and seed survival as well as the different environmental conditions.

The results from the study certainly back up the concept of Lantana being a difficult weed to control. As well as the seeds being bird-dispersed and thus requiring control measures for a wide area, the study showed that seedlings germinate in a variety of conditions, although are most successful in warmer and lighter conditions, suggesting that the closer the seeds are to the surface the more likely they will germinate and are most likely to germinate during the Summer months. The Lantana seedling emergence was affected by many factors, although it was lower for the more deeply buried seeds, suggesting that forms of control through seed suppression, such as mulching could be beneficial in controlling Lantana. Alternatively the seeds could be encouraged to the surface to stimulate emergence and then treat the weeds as they emerge. Through regression techniques in GenStat the researchers discovered that seedling emergence could continue for 3 – 11 years (depending on the depth of the seed) after weed management programmes have removed the actual Lantana plants. The details and information discovered on the ecology of the Lantana suggest that to effectively control or eliminate this weed farmers and agricultural producers would need to employ on-going management techniques and intensive follow-up on the weed management programmes, as the seed survival and persistence of the Lantana appears to be far greater than first thought.

Our thanks to Dr Gabrielle Vivian-Smith and her colleagues at Alan Fletcher Research Station for their help in producing this story.

The full paper is available here.

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