In a study titled PERSISTENCE OF HERBICIDES 'ORANGE' AND 'WHITE' IN A FOREST SOIL, testing was done just south of Manila. The Report states that the mixtures were "...applied during the evening of 18th January 1972 (overcast, cool); the remainder the following morning (sunny, warm)."
It goes on to say "The site near Los Banos kindly provided by the University of the Philippines, College of Agriculture, was located in a clearing in the forest reserve."
Reference is made to tests in the UK. It's good reading. There will be more to follow for all you interested horticulturists.
NAS Committee on the effect of Herbicides in Vietnam: Preliminary Proposals for Studies on the Persistence of Herbicides in Forest and Mangrove soil
Investigations relating to the persistency of herbicides: Experimental procedures for sampling and determination of residues
National Academy of Sciences Committee on effects of herbicides in Vietnam: Persistence of Herbicides ‘Orange’ and ‘White’ in a forest soil