Glyphosate-based herbicides (GBHs) are the most frequently used
herbicides globally. They were launched as a safe solution for weed
control, but recently, an increasing number of studies have shown the
existence of GBH residues and highlighted the associated risks they pose
throughout ecosystems. Conventional agricultural practices often
include the use of GBHs, and the use of glyphosate-resistant genetically
modified crops is largely based on the application of glyphosate, which
increases the likelihood of its residues ending up in animal feed.
These residues persist throughout the digestive process of production
animals and accumulate in their excretion products. The poultry
industry, in particular, is rapidly growing, and excreted products are
used as plant fertilizers in line with circular food economy practices.
We studied the potential effects of unintentional glyphosate
contamination on an agronomically important forage grass, meadow fescue (Festuca pratensis) and a horticulturally important strawberry (Fragaria x vescana)
using glyphosate residues containing poultry manure as a plant
fertilizer in a common garden experiment. Glyphosate in the manure
decreased plant growth in both species and vegetative reproduction in F. x vescana.
Furthermore, our results indicate that glyphosate residues in organic
fertilizers might have indirect effects on sexual reproduction in F. pratensis and herbivory in F. x vescana
because they positively correlate with plant size. Our results
highlight that glyphosate can be unintentionally spread via organic
fertilizer, counteracting its ability to promote plant growth.