Beetle banks

How

August and September are the best months to establish the grass sward that forms a beetle bank.

Beetle banks are created by ploughing furrows that point towards each other during cultivation to create a raised bank of about 0.4m along the plough line. The headland at each end of the beetle bank can remain cropped. Leaving a gap of no more than 25m between the end of the beetle bank and the field margin will reduce ground predators such as stoats accessing the beetle bank. The bank should be seeded with a native grass seed mix with up to 30% tussock-forming species such as cocksfoot or timothy. The rest of the mix can consist of fescues and bents. The seed should be broadcast immediately after cultivation at a rate of 70kg/ha for good establishment. Although more costly, mixes can include tall, tussock-tolerant wildflowers which can encourage other pest predators such as hoverflies and parasitic wasps.

In the first summer, 3 cuts may be necessary when the sward reaches 10cm in height, to encourage grasses to tiller and to help control invasive annual weeds. Once established, cut the grass strips as little as possible as established tussocks are key overwintering features for many of the species that will utilise the beetle bank. Cutting on a 3 year rotation is ideal, and this will help to produce a diverse grass structure which will support a wider range of wildlife.

Cutting should take place during autumn, before insects look to find shelter over winter.

To improve the degree of natural pest control in large arable fields, beetle banks should be located through the middle of fields larger than 20ha, between tramlines so that the crop can still be sprayed on either side with minimal disruption to spraying operations. To intercept surface run-off, beetle banks should run along the contours of the slope so that the raised bank holds up water running down the slope and increase the rate of infiltration into the soil.

Beetle banks are particularly vulnerable to the effects of pesticide drift where they are sprayed on either side. This can reduce their ability to harbour beneficial insects and spiders. Adding grass buffer strips to both or either sides can help to alleviate this. On light soils with a low weed burden, conservation headland management on either side of a beetle bank will enhance its value for insects and birds whenever the adjacent crop is a cereal. Alternatively, more habitat diversity can be created by establishing flower-rich habitats on the adjoining sides to further bolster populations of beneficial insects.