Stop using herbicides on pavements and road verges

Overall effectiveness category Awaiting assessment
Number of studies: 2
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How is the evidence assessed?

Effectiveness

not assessed
Certainty

not assessed
Harms

not assessed

Calculating overall effectiveness category

Background information and definitions

Plants growing within urban landscapes, such as along pavements or road verges, can provide important habitat for wildlife, including butterflies and moths, but these areas are often subject to intense management, including regular doses of herbicide to control plant growth. However, herbicides can have lethal or sub-lethal effects on butterflies and moths (Russell & Schultz 2010, Schultz et al. 2016). Stopping the use of herbicides on pavements and road verges may help to support butterfly and moth populations in urban areas.

For other management options for road verges, see “Residential and commercial development – Alter mowing regimes on greenspaces and road verges” and “Transportation and service corridors – Restore or maintain species-rich grassland along road/railway verges”.

^{Russell C. & Schultz C.B. (2010) Effects of grass-specific herbicides on butterflies: an experimental investigation to advance conservation efforts. Journal of Insect Conservation, 14, 53–63.}

^{Schultz C.B., Zemaitis J.L., Thomas C.C., Bowers M.D. & Crone E.E. (2016) Non-target effects of grass-specific herbicides differ among species, chemicals and host plants in Euphydryas butterflies. Journal of Insect Conservation, 20, 867–877.}

Study locations

Key messages

Two studies evaluated the effects on butterflies and moths of stopping the use of herbicides on pavements and road verges. One study was in the USA and the other was in Canada.

COMMUNITY RESPONSE (2 STUDIES)

Richness/diversity (2 studies): One replicated, paired, site comparison study in the USA found that restored roadside prairies where herbicide application was restricted had a greater species richness of butterflies than verges dominated by non-native weeds and grasses with no restrictions on herbicide application. One replicated, site comparison study in Canada found that transmission lines (road verges and power lines) which were neither sprayed with herbicide nor mown had a similar species richness of butterflies to sprayed and mown transmission lines.

POPULATION RESPONSE (2 STUDIES)

Abundance (2 studies): One replicated, paired, site comparison study in the USA found that restored roadside prairies where herbicide application was restricted had a greater abundance of butterflies than verges dominated by non-native weeds and grasses with no restrictions on herbicide application. One replicated, site comparison study in Canada found that transmission lines (road verges and power lines) which were neither sprayed with herbicide nor mown had a greater abundance of northern pearl crescent and pearl crescent butterflies, but similar total butterfly abundance, compared to sprayed and mown transmission lines.
Survival (1 study): One replicated, paired, site comparison study in the USA found that butterflies had a lower mortality risk on restored roadside prairies where herbicide application was restricted than on verges dominated by non-native grasses with no restrictions on herbicide application.

BEHAVIOUR (0 STUDIES)

About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

Supporting evidence from individual studies

A replicated, paired, site comparison study in 1998 in 12 road verges in Iowa, USA (Ries et al. 2001) found that restored roadside prairies where herbicide application was restricted had a higher abundance and species richness of habitat-sensitive butterflies than verges dominated by non-native weeds or grasses with no herbicide restrictions. On restored roadside prairies with herbicide restrictions, both the abundance (2.3 individuals/plot) and species richness (1.6 species/plot) of habitat-sensitive butterflies was higher than on roadsides with no herbicide restrictions and dominated by weeds (abundance: 1.4 individuals/plot; richness: 0.9 species/plot) or grasses (0.5 individuals/plot; 0.7 species/plot), and not significantly different from remnant prairies (1.6 individuals/plot; 1.7 species/plot). In addition, mortality risk was lower on prairie or weedy road verges than on non-native grass verges (data presented as model results). On eight well-established, restored prairie road verges (>0.5 km long) and four native (never ploughed) prairie verges dominated by native prairie vegetation, the use of herbicides was restricted. Roadside vegetation (>6 m wide) within 1.6 km of the 12 prairies, but with no restrictions on herbicide use, was classified as “weedy” (>20% non-native legumes) or “grassy” (dominated by non-native grasses). From June–August 1998, butterflies were surveyed nine times in 1–3 plots/habitat (restored prairie, native prairie, weedy, grassy) at each of 12 sites. Plots were 50 × 5 m, >50 m apart and >500 m from a different verge habitat. In addition, three plots in each of four native prairie remnants (2–16 ha) were surveyed. Roadkill butterflies were surveyed six times along both road edges next to each plot.
Study and other actions tested
Referenced paper
Ries L., Debinski D.M. & Wieland M.L. (2001) Conservation value of roadside prairie restoration to butterfly communities. Conservation Biology, 15, 401-411.
A replicated, site comparison study in 2007–2008 along 52 road verges and power lines (collectively “transmission lines”) in Manitoba, Canada (Leston & Koper 2016) found that transmission lines which were not sprayed with herbicide and left unmown had more northern pearl crescent Phyciodes morpheus and pearl crescent Phyciodes tharos butterflies than frequently sprayed lines mown twice/year, but herbicide use did not affect the abundance or species richness of other butterflies. There were more crescent butterflies on unsprayed, unmown transmission lines (2.7 individuals/visit) than on frequently sprayed lines mown twice/year (0.1 individuals/visit). However, the abundance and species richness of other native butterflies was not significantly different between transmission lines which were not sprayed or mown (abundance: 11 individuals/visit; richness: 32 species), unsprayed and mown (14 individuals/visit; 21 species), infrequently sprayed and mown (11 individuals/visit; 27 species), or frequently sprayed and mown (10 individuals/visit; 21 species). See paper for species results. Fifty-two road verges and power lines (>30 m wide, >400 m long) were managed in one of four ways: 21 were neither sprayed with herbicide nor mown, but some trees were removed; 14 were sprayed frequently with herbicide and mown twice/year with cuttings left on site; 10 were sprayed infrequently with herbicide and mown once/year with cuttings left on site; seven were not sprayed and were mown once/year with cuttings baled and removed. From 15 June–15 August 2007–2008, butterflies were surveyed on one 400- or 500-m transect at each site 2–4 times/year.
Study and other actions tested
Referenced paper
Leston L. & Koper N. (2016) Urban rights-of-way as reservoirs for tall-grass prairie plants and butterflies. Environmental Management, 57, 543-557.

Please cite as:

Bladon A.J., Bladon, E. K., Smith R.K. & Sutherland W.J. (2023) Butterfly and Moth Conservation: Global Evidence for the Effects of Interventions for butterflies and moths. Conservation Evidence Series Synopsis. University of Cambridge, Cambridge, UK.

Where has this evidence come from?

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This Action forms part of the Action Synopsis:

Butterfly and Moth Conservation

Related Actions

	Actions	Effectiveness	Studies	Category
	Stop using pesticides as seed dressings and sprays in flower beds and greenspace Action Link	Evidence not assessed	1	Synopsis Link
	Stop using herbicides on pavements and road verges Action Link	Awaiting assessment	2	Synopsis Link