A new research paper published in the journal Weed Science has found that herbicide residues persist in spray packs even after thorough washing out, with implications for home gardeners’ cultural practices.
The multi-year study tested the residual levels in spray packs of two herbicides commonly used as glyphosate alternatives, dicamba and 2,4-D.
The researchers looked at the difference in residual herbicide levels between several different plastics commonly used in the manufacture of spray packs – PVC, polyethylene, polyurethane, PVC/polyurethane blends and synthetic rubbers.
They found all plastics retained various levels of dicamba and 2,4-D, with the PVC/polyurethane blends and synthetic rubber recording the highest levels.
The researchers also tested residue levels after washing out with only water and an ammonia/water blend. Interestingly, they found no change in the levels of residue between these two conditions, citing instead the quality of the plastics and synthetic rubbers used in sprayers as the major determining factor.
Using electron microscopy, they determined the inner walls of PVC/polyurethane blends and synthetic rubbers contained tiny imperfections that provided herbicide residues a place to persist, regardless of how the sprayers were cleaned out.
While polyethylene hoses contained the least imperfections, and hence recorded the lowest levels of residues, they were not free of them.
The implications for home gardeners are clear – keep separate spray packs for herbicide, insecticide and fertiliser applications if you use them at home.