RELATION BETWEEN VOLATILITY RATING AND COMPOSITION OF PHENOXY HERBICIDE ESTER FORMULATIONS

A CIPAC/AOAC test with tomato plants is used to specify the volatility ratings of herbicide ester formulations. This work compares the tomato plant test with an alternative chemical one. The concentrations of esters and the effective molecular weight and density of each formulation were used with the ester vapour pressures to calculate its herbicide vapour pressure as complete, and evaporated formulations. The range was from 28.8 mPa (at 257deg;C) for a mixture of 2,4–D esters to 0–07 mPa (at 25°C) for a 2,4,5–T‐(iso‐octyl) formulation, as complete formulations, and 35‐5 and 0–16 mPa (at 25°C) as evaporated ones. A value of 0–6 mPa (at 25°C) was selected on the basis of the tomato plant test as the cut‐off area for low‐volatile esters and is recommended to be included in specifications for herbicide esters. Formulations with a herbicide vapour pressure above 3.3 mPa (at 25°C) are high‐volatile ones according to the tomato plant test, while between 0–6–3.3 mPa (at 25°C) is a borderline region where the test gives mixed results. Levels of 2,4–D‐ethyl and methyl were added to pure 2–ethylhexyl esters of 2,4–D and a 2,4,5–T‐(iso‐octyl) formulation to find what level of contamination would change the rating of these esters from low to high volatile. Formulations of 2,4–D‐(iso‐octyl) should not contain more than 11 g litre−1 2,4–D as methyl ester or 2.0 g litre−1 2,4–D as ethyl ester. Formulations of 2,4,5–T‐(iso‐octyl) should not contain more than 26 g litre−1 2,4–D as methyl ester or 4.7g litre−1 2,4–D as ethyl ester. Copyright © 1990 Wiley Periodicals, Inc., A Wiley Company