Impact of different meadow mowing techniques on field invertebrates

Published source details Humbert J.Y., Ghazoul J., Sauter G.J. & Walter T. (2010) Impact of different meadow mowing techniques on field invertebrates. Journal of Applied Entomology (formerly Zeitschrift für angewandte Entomologie), 134, 592-599.
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This study is summarised as evidence for the following.

	Action	Category
	Use motor bar mowers rather than rotary mowers Action Link
	Raise cutting height on grasslands Action Link
	Use mowing techniques to reduce mortality Action Link

Use motor bar mowers rather than rotary mowers

A replicated, randomized, paired, controlled study in 2007–2008 in Switzerland (Humbert et al. 2010) found that harvesting meadows using a hand-pushed bar mower killed or injured fewer large white Pieris brassicae caterpillars than using a tractor-pulled rotary mower. Fewer caterpillars were killed by a bar mower (20%) than by a rotary mower used without (35–37% killed) or with (41–69% killed) a rear flail conditioner attached. Similarly, fewer wax models were damaged by the bar mower (11%) than the rotary mower used without (17% damaged) or with (28% damaged) a conditioner. In 2007–2008, in each of nine meadows, three 2.5-m-long plots were randomly assigned to three mowing treatments: 1.7-m-wide hand-pushed bar mower, or 2.5-m-wide tractor-pulled rotary drum mower without or with a rear flail conditioner, all cut to 6 cm. Before mowing, half of 200 wax caterpillar models (100 large and 100 small) were placed on the ground and half were tied to vegetation 20–30 cm high in each plot. In 2008, on five meadows, large white caterpillars were placed on the ground (50 caterpillars) and in the vegetation (50 caterpillars) in each plot. After mowing, wax models and caterpillars that survived were checked for damage or injuries.

(Summarised by: Andrew Bladon, edited from Farmland Synopsis)
Raise cutting height on grasslands

A replicated, randomized, paired, controlled study in 2007–2008 in Switzerland (Humbert et al. 2010) found that raising the cutting height when mowing meadows did not increase the survival of large white Pieris brassicae caterpillars. The proportion of large white caterpillars killed by mowing at 9 cm (30–43%) was not significantly different from the proportion killed by mowing at 6 cm (35–37%). Similarly, the proportion of wax models damaged by mowing at 9 cm (16.9%) was not significantly different from the proportion damaged by mowing at 6 cm (17.4%). In 2007–2008, in each of nine meadows, two 2.5-m-long plots were randomly assigned to either 9 cm or 6 cm cutting height, and mown with a 2.5-m-wide tractor-pulled rotary mower. Before mowing, half of 200 wax caterpillar models (100 large and 100 small) were placed on the ground and half were tied to vegetation 20–30 cm high in each plot. In 2008, on five meadows, large white caterpillars were placed on the ground (50 caterpillars) and in the vegetation (50 caterpillars) in each plot. After mowing, wax models and caterpillars that survived were checked for damage or injuries.

(Summarised by: Andew Bladon, edited from Farmland Synopsis)
Use mowing techniques to reduce mortality

A randomized replicated trial in 2007 and 2008 in Switzerland (Humbert et al. 2010) found that harvesting meadow plots using a hand-pushed bar mower killed or injured on average 20% of caterpillars (Lepidoptera) added to plots before mowing, compared to 37% when using a tractor-pulled rotary drum mower, and 69% if a conditioner was attached to the rotary mower. Using a conditioner also increased the proportion of damaged wax invertebrate models from on average 11% (bar mower, no conditioner) to 30% (rotary mower with conditioner). Large (4 cm) invertebrate models were damaged more often than small (2 cm) models. Caterpillars and models placed on the ground or in vegetation (30 cm high) before mowing were affected differently by mowing treatments. Organisms on the ground were strongly impacted by tractor wheels, whilst those in vegetation were damaged by the mower/conditioner. Cutting height did not affect mortality in this study, but the authors note it is likely to be important for larger animals. Nine meadows were studied, with four 2.5 m-long plots each. There were four mowing treatments: hand-pushed bar mower (cutting height 6 cm, 1.7 m-wide), tractor-pulled rotary drum mower (2.5 m-wide) with two cutting heights 9 cm and 6 cm (one with, one without conditioner). Before mowing, 50 small and 50 larger wax invertebrate models were placed either on the ground or tied to vegetation 30 cm high. In 2008 on five meadows, large white butterfly caterpillars, Pieris brassicae, were placed on the ground (50 caterpillars) and in the vegetation (50 caterpillars). After mowing, both wax models and caterpillars that survived mowing were checked for injuries.