Managing orchard groundcover to reduce pollinator foraging post‐bloom

Abstract

BACKGROUND: Agricultural insecticides are believed to play a role in global pollinator decline. In mass-flowering orchard crops, recommendations to reduce exposure of pollinators to insecticides include spraying at periods when bees aren't foraging, such as dusk and dawn and outside of crop flowering times. However, the presence of flowering weeds within orchards mean pollinators may still be found foraging throughout the growing season, increasing the likelihood that exposure will still occur. We hypothesized that removing these weeds within orchard groundcover may reduce pollinator foraging post-bloom and thus reduce exposure of this group to pesticides. We tested this hypothesis by using herbicide to remove flowering broadleaf weeds in the sod middles ('groundcover') between rows of a nectarine orchard in New Jersey, USA, and assessing the effect on pollinator visitation via three different methods.RESULTS: Significantly lower abundance, richness, diversity, and evenness of pollinators were found in plots where herbicide treatment had removed the majority of flowering weeds, compared to untreated plots. This was the case for bees, and for pollinators overall, and was reflected in both visual observations and active sampling through sweep netting. Passive sampling with blue vane traps failed to detect a difference between treatments.CONCLUSION: Groundcover management in orchards is often employed as part of integrated pest management programs to remove alternative host plants of insect pests. The findings of this study show that it is also effective in reducing post-bloom pollinator foraging in orchards, thus potentially preventing exposure of these beneficial organisms to harmful insecticides.

Removing non‐crop flowers within orchards promotes the decline of pollinators, not their conservation: A comment on McDougall et al. (2021)

“…Compliance with regulations should occur through reductions in insecticide and herbicide use, and via improvements in their safety to non-target organisms McDougall et al (2021) suggest that compliance with US-EPA regulations ('minimize exposure of this product to bees and other pollinators when they are foraging on pollinator attractive plants around the application site') would be facilitated to farmers by reducing the abundance and diversity of pollinators in their crop fields via eliminating flowering ground cover. In the introduction, the authors state: 'There is growing recognition that IPM tactics should be combined with pollinator management strategies (…) and thus if this technique can meet both objectives it would be a potentially valuable tool in the repertoire of crop managers'.…”

“…We instead advocate for providing feeding resources to farm‐associated pollinators and other beneficial fauna through the promotion of flowering herb cover within crop fields (Requier et al, 2015), as well as reducing herbicide and pesticide use (EC, 2022; Goulson et al, 2015). In the following paragraphs, we give arguments against the proposal of McDougall et al (2021):…”

“…Available nectar and pollen sources should be maintained as long as possible throughout the growing season, especially before the bloom of early flowering temperate crops, with little time between pollinator emergence and crop bloom (Campbell et al, 2017). Considering the great importance that diverse communities of pollinators can have to crop pollination, as highlighted by McDougall et al (2021) for their own study system, eliminating a large portion of pollinator food resources could negatively impact their contribution to crop yields.…”

“…This can be done, for example, by reducing the use of herbicides and insecticides, increasing the biodiversity within crop fields, and avoiding bare soil with permanent vegetation cover (Brodt et al, 2011; Garibaldi et al, 2017; Horrigan et al, 2002; Kleijn et al, 2019; Kremen et al, 2012). In a recent paper by McDougall et al (2021) published in the journal ‘ Pest Management Science’ entitled ‘Managing orchard groundcover to reduce pollinator foraging post‐bloom’, the authors propose removing flowering ground herbs once the mass flowering period of the crop ends as a bee conservation strategy. With a multiyear field‐experimental approach, they conclude this practice reduces the abundance and diversity of pollinators within the crop during the post‐bloom stage, thus, reducing their exposure to pesticides.…”

“…Habitat loss is among the main drivers of pollinator decline in agricultural landscapes, which is mainly mediated by the reduction of floral and nesting resources associated with intensive agriculture (González‐Varo et al, 2013; Parreño et al, 2021; Potts et al, 2010). The strategy proposed by McDougall et al (2021) entails the removal of ground cover through the application of herbicide after the mass flowering of crops, therefore, shortening the availability of nectar and pollen to the broad range of pollinators distributed within crop fields. McDougall et al (2021) defend this management practice as a conservation tool by assuming a relocation of pollinators from orchards to surrounding nominally pesticide‐free seminatural areas after removal of ground cover.…”