I did some work in manitoba Canada in the 1990's - tough to simulate but short story is that there could be some effect - especially for low water volumes and for contact herbicides - I never published the work though - sorry

Rene Van Acker

University of Guelph

Canada

In  WEED SCIENCE 54(NOV 2006):1132-1136 ·is article "Soil dust reduces glyphosate efficacy".

best regards

Adam Dobrzanski

Riar et al 2010 Agronomy journal

Likewise unpublished but have done work in the glasshouse showing that showing that dust form soil blown onto plant surfaces can significantly reduce uptake into plant and so activity of diquat and paraquat by the organic matter and clays in the soil dust binding to the herbicides.  In a slightly different way it is well known that activity of glyphosate can be substantially reduced by binding to calcium and magnesium and other polyvalent cations found both in dust and hard waters - there are several publications on this throughtout the literature over the last 30 years  it is the reason that throughout the USA Ammonium sulphate is always tankmixed with any application of glyphosate and indeed many other herbicides.  Activity of bentazon can be lost by the formation of a less rapidly taken up sodium salt being formed when formulated in high sodium water and the inherent photo instability of the herbicide then renders it susceptible to photodegradation on the plant surface leading to loss of a significant amount of final activity - again this has been published quite some time ago I don't have the reference to hand.  All these reasons contribute to why we at Syngenta are very careful that our glasshouse plants for research screening are not rose watered from above with hard or dirty water.  best regards  Gavin