Pre-emergence weed control in flax with sulcotrione

Pre-emergence weed control options in flax are very limited with only two soil-applied herbicides, linuron and lenacil, and their mixture being available. Sulcotrione, formerly coded as ICIA0051, is a key postemergence maize herbicide since 1993; however, field screening trials conducted at Melle during the 1989 growing season had revealed excellent selectivity to fibre flax of sulcotrione when applied preemergence. Therefore, ten herbicide experiments have been carried out over the 1992-1995 period, to evaluate the efficacy and selectivity of pre-emergence application of sulcotrione. Four experiments were located at Melle (Province East-Flanders; sandy loam soil; fibre flax) and six at Gistel, Houtem (fibre flax at both locations) or Koksijde (linseed flax) (all these locations in the Province of West-Flanders on sandy clay to heavy loam soil). At Melle, sulcotrione (375 g per ha) and its mixtures (at 300 g per ha) with linuron ( 125 g per ha) or lenacil (400 g per ha) were more effective than the reference treatment linuron + lenacil (125 + 500 g per ha) against Chenopodium album L., Solanum nigrum L., Polygonum convolvulus L. and Polygonum persicaria L. but control of Polygonum aviculare L. was not better, while Matricaria recutita L., Stellaria media L. and Poa annua L. could escape to a greater extent, especially when sulcotrione was applied alone. At Gistel, Houtem and Koksijde (heavier soil with higher herbicide rates), sulcotrione (600 g per ha) and its mixtures (at 400 g per ha) with linuron (175 g per ha) or lenacil (500 g per ha) were better than the standard treatment linuron + lenacil (175 + 600 g/ha) against Atriplex patula L., Veronica hederifolia L., Polygonum spp. (P. aviculare, P. convolvulus and P. persicaria), Fumaria officinalis L., Lamium purpureum L., Stellaria media and Mercurialis annua L. but weaker against Alopecurus myosuroides Huds. Neither visual injury during the growing season nor any adverse effect on straw and seed yields could be detected with sulcotrione. Taken into account fibre yield and quality, on light soils, sulcotrione rate must be limited to 300 g per ha and only its mixture with lenacil is recommended, whereas on heavier soils, its rate can go up till 400 g per ha in mixture with linuron or lenacil. Pre-emergence sulcotrione had no consequences for later postemergence treatments