The identification of ryegrass biotypes resistant to glyphosate is causing changes in weed management in apple orchards. Three experiments were carried out to determine the GR50 of the biotypes, to grass herbicides and dry matter accumulation. The first experiment tested different rates of glyphosate. Their effects on GR50 dry matter accumulation by the biotype were assessed. In the second experiment different rates of glyphosate and grass herbicides were tested: glyphosate, haloxyfop-r, diclofop, fluazifop-p, fenoxaprop-p and paraquat. A third experiments was carried out under glasshouse conditions to determine the curve of dry matter accumulation. The results showed GR50 of 287.5 and 4,833.5 g e. a. ha-1 of glyphosate for the sensitive and resistant biotypes, respectively. The results showed that the resistant factor (RF) was 16.8 and that the resistance mechanism alters the biological characteristics of the resistant biotype affecting its sensitivity to grass herbicides.
herbicides; EPSP inhibitors; grass herbicides; apple orchards
