Beneficials on farmland: identification and management guidelines (HGCA Summer 2008)

Alternative prey

Pests often occur sporadically during the growing season. They have shorter life cycles than beneficials. Other food sources (alternative prey) within and outside fields are needed to maintain beneficial populations.

Many agri-environment options encourage alternative prey both in non-crop habitats and within crops. It is easier to encourage beneficials in non-crop habitats than within crops.

Non-crop options, such as conservation headlands and unmanaged field corners, support alternative prey. Arable flowers provide pollen and nectar. Such areas are used by birds, butterflies, small mammals and other wildlife.

Within crops, several agri-environment  options help increase alternative prey within crops. These include fallow plots, overwintered stubbles, extensively farmed crops and minimum tillage. Up to 500 insect species, most of which beneficials eat, have been found within wheat fields. Many forage upon weeds, or detritus, and so are sensitive to farming practices.

Targeting weed control only at the most competitive weeds and using selective products, lower doses and fewer applications each season may allow a diversity of uncompetitive weeds to develop. Only use this approach where noxious weeds, eg black-grass and cleavers, are absent. Weed seeds are also important food for invertebrates and birds.

Herbicide inputs may be reduced within fields to encourage invertebrates. Highest numbers of the most desirable weeds survive when only one application is made each season. Inputs can be reduced without compromising yield on some soils where weed pressure is low.

Further details are available in Enhancing Arable Biodiversity: Six practical solutions for farmers, SAFFIE/HGCA (2007).

Plant species by desirability for biodiversity

Group 1 – Very desirable
All rare arable flowers
Annual meadow grass
Black bindweed
Common fumitory
Fat hen
Pale persicaria
Group 2 – Desirable
Field pansy
Pineapple weed
Scented mayweed
Scentless mayweed
Wild pansy
Group 3 – Neutral
All species not included in groups 1, 2 and 4
Volunteer kale
Volunteer linseed
Group 4 – Not acceptable to leave in any numbers
Awned canary grass
Broad-leaved dock
Common couch
Creeping soft-grass
Creeping thistle
Great brome
Italian rye-grass
Meadow brome
Soft brome
Spear thistle
Sterile/barren brome
Volunteers – beans, potatoes, sunflowers, oilseed rape, cereals
Wild oat
Winter wild oat

Source: HGCA Project Report 416 (2007)

Conservation headland

Field corner with flowers

Organic matter – food for many detritus-feeding insects – can be boosted by returning crop residues and applying manure. Minimal tillage helps to ensure that organic matter remains available near the surface.

Crop debris on surface after minimal tillage

More mobile beneficials may forage outside the crop. Hedgerows and flower-rich margins provide an abundance of alternative prey, as do game and wild bird cover crops with a weedy understorey.

Weedy game crop

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