Management Options for Hedgerow Vegetation: Combining Weed Control with Habitat Improvement for Predatory Arthropods.

Abstract

In a project designed to explore possibilities for botanical improvement of hedge-bottom vegetation, with the added aim of enhancing resources for aphid predators, nine different management options were compared in a replicated experiment along the length of a hedge. In all treatments the hedge-bottom was extended from approximately 0.5 m to 2 m. There were three unsown treatments: natural regeneration, natural regeneration with frequent cutting during establishment and natural regeneration with a single selective application of herbicide. The six unsown treatments first had the existing vegetation removed with glyphosate and were then re-sown with cock's foot (Dactylis glomerata), red fescue (Festuca rubra), false oat-grass (Arrhenatherum elatius), Yorkshire fog (Hocus lanatus) and a mixture of all four species; the sixth sown treatment had a mixture of the four grasses and was cut frequently during establishment.
Sampling of overwintering polyphagous arthropods was carried out in the existing hedge-bottom before treatment and for the successive four winters. Hedge-bottom extension was considered likely to increase the availability of overwintering habitat for polyphagous predators, but none of the treatments appeared to offer any advantage over simple natural regeneration. Proximity to the hedge and the depth of the sod layer had a positive effect on predator numbers. An experiment comparing different methods of sampling overwintering arthropods showed that, unlike 0.01 m² circular cores and suction samples, 0.04 m² square spade samples generally gave data that was suitable for parametric statistical testing. Botanical surveys were carried out during June for the three summers following treatment. None of the treatments had an overall advantage over natural regeneration alone, apart from the herbicide treatment, which gave the best control of cleavers (Galium aparine). This treatment also carried the highest densities of couch grass (Elymus repens). Aphidophagous hoverflies were observed feeding on a wide range of flowers in an agricultural habitat, but showed a preference for certain flower species both in the field and in the laboratory. Flower choice by the hoverfly (Episyrphus balteatus) was influenced by both the phenology of pollen production and some degree of visiting constancy, although there was no evidence of any learning ability by this species. Laboratory experiments revealed no difference in the nutritional value of pollen from different flower species for E. balteatus, although the pollen grains of common mallow (Malva moschata) were too large to be ingested in sufficient quantity for ovarian development and oogenesis.
It was concluded that extension and natural regeneration of the hedge-bottom would, in most situations, result in adequate improvement of the hedge-bottom flora and provision of resources for aphid predators.