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Planting wildflowers on farmland helps spiders

14 February 2013, by Valerie Nadeau

By encouraging wildflowers to grow on parts of their land not used for crops, farmers could increase spider numbers, which help to control crop pests, say scientists.

Crab spider

Crab spider.

UK researchers have found that by planting wildflower seeds and using a herbicide that reduces grass growth, they can enhance the number of wildflowers growing in existing strips of grass at the edges of farmers' fields.

This increases the number of spiders living in these grass strips, which then feed on crop pests like aphids.

Spiders play an important role in UK ecosystems, both as predators of small insects and as prey for larger animals. But like other invertebrates such as bees and butterflies, their numbers are declining because of modern farming practices.

The UK government has responded to declining invertebrate numbers by launching agri-environment schemes (AES), which offer farmers money to manage their land in an environmentally friendly way. One example is planting strips of grass around their crops to provide a habitat for a variety of insects. Although these grass strips have been highly popular, with approximately 29,000 hectares of grass buffer strips planted by 2009, they've done little to reverse the decline in insect numbers.

'Grass buffer strips are very popular under UK agri-environment schemes, and there's lots and lots of them being put in, but one of the problems is that they don't tend to do a great deal for biodiversity,' says Dr Robin Blake, who was at Reading University during the study but is now at Syngenta.

This latest research shows that spider numbers in grass buffer strips can be boosted by encouraging wildflowers to grow. 'The wildflowers bring in pollinators and other insects, and that therefore increases the amount of prey available for the spiders,' says Blake.

Wildflower meadow

Wildflower meadow.

But the research also shows that simply planting wildflower seeds into existing grass buffer strips is not enough, because of the dominant nature of the grasses growing there. To encourage growth of wildflowers, the researchers cultivated the grass strips before planting wildflower seeds, and used a selective herbicide that reduces grass growth.

Their results reveal that this produced more wildflowers and more spiders than planting wildflower seeds without using a grass-specific herbicide. Their findings also demonstrate that the herbicide has no obvious negative effect on the spiders.

The technique provides farmers with a low-cost way to improve the biodiversity of their land, without the need to plant new buffer strips. This is not only an important conservation tool, but also has an additional benefit for farmers, as spiders are natural predators of many crop pests.

'There needs to be a lot more work from a policy point of view to see if there are cheap and easy ways like this that we could improve farmland biodiversity,' says Blake.

However, the study only focussed on spiders. Before implementing schemes like this on a wider scale, scientists need to look at the effects of grass-specific herbicide on other invertebrates.
The research is published in Agricultural and Forest Entomology, and was funded by the Biotechnology and Biological Sciences Research Council (BBSRC) and Syngenta.

Blake, R. J., Woodcock, B. A., Westbury, D. B., Sutton, P. and Potts, S. G. (2013), Novel management to enhance spider biodiversity in existing grass buffer strips. Agricultural and Forest Entomology, 15: 77-85. doi: 10.1111/j.1461-9563.2012.00593.x

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