The relationship between the entry of isoproturon into Alopecurus myosuroides and its effect on growth and CO₂ fixation

Abstract

S U M M A R YAlopecurus myosuroides (blackgrass) was grown in nutrient and with isoproturon added to the solution when plants had three leaves. The transpiration stream coefficient factor was calculated over a period of 96 h after treatment to be approximately 1. On this basis isoproturon entry into A. myosuroides was estimated using data for water loss through plants and there was a linear relationship between herbicide entry and plant weight 14 days after treatment. Treatment for at least 7 days with isoproturon at a dose of 1 pg a.i./15 ml nutrient solution (= 0.32 x 1 0 -6~) before returning plants to fresh nutrient was necessary for damage to be still evident after 14 days. This time period corresponded with the reduction of C 0 2 exchange to zero as measured by infra-red gas analysis. Some recovery occurred from 6 h treatment with 120 pg a.i. isoproturon/l5 ml nutrient solution when assessed after returning plants to untreated nutrient for 14 days. A quicker depletion in C 0 2 uptake by blackgrass occurred when both the primary and secondary roots were treated compared with secondary alone but eventually the levels reached were similar. The 'CALF' model predicted much higher concentrations of isoproturon than appeared necessary to damage A. myosuroides. This suggests a major influence of climate on the plant and this and other interactions are discussed.

The interaction between planting depth of four winter wheat cultivars, Alopecurus myosuroides Huds. and Bromus sterilis L. and their susceptibility to post‐emergence applications of isoproturon and chlorotoluron

“…However, the safety margin may not be very great. For example, Blair (1987) showed that, in nutrient culture, A. myosuroides could be severely damaged by 0-07 ppm isoproturon, and in the present experiments wheat was significantly damaged by 0-1-0'2 ppm isoproturon. Thus any enhancement of the selectivity by physical factors such as deeper planting or root morphology will be beneficial.…”

“…Isoproturon inhibits photosynthesis (Blair, 1987). Therefore, CO2 exchange was measured by IRGA and used as an indicator of isoproturon entry into the plant.…”

“…Addala et al (1985) reported a similar response of A. myosuroides to chlorotoluron when plants were grown with and without protection of the shoot zone by a straw. In contrast, B. sterilis was much less sensitive to isoproturon (Henly etal., 1985) than was A. myosuroides (Blair, 1987), and there is no product label recommendation for B. sterilis control. Our experiment showed that B. sterilis plants that arise from a shallow sowing are more susceptible to isoproturon than those from deeper sowings, but that the tolerance of this weed is similar to that of wheat.…”