Growth regulators for cereal and oil crops on the basis of 2,3-dichloroisobutyric acid and chlormequat chloride and residue analyses in the grain of oat

Abstract

Field plot experiments were established for studying the influence of growth regulators MLU 208, MLU 2081 [various mixtures of 2,3-dichloroisobutyric acid (DCiB) with chlormequat chloride (CCC)] and CCC on length of shoot axis, susceptibility to lodging and grain yield of oat (Avena sativa) and winter oilseed rape (Brassica napus). Oat grains were also analysed for residues. With lodging-resistant oat varieties the regulators MLU 208 and MLU 208L caused stem reductions of 10% and yield increases up to 6.5% despite the fact that the untreated controls showed hardly any lodging. CCC had no yield-increasing effect, although a stem reduction of approximately 8% was recorded. Tests with a variety of poor stem stability resulted in stem length reductions of 10%, prevented lodging and increased grain yields by 7–9.5%. Applying MLU 2081 to oilseed rape prior to flowering shortened the stem by 8–11% and contributed to a grain yield increase of about 5–8%. For early (EC 31/32) and late (EC 45) application of MLU 208 and MLU 208L DCiB-residues of about 0.1 mg kg⁻¹ were measured. CCC residues increased with increasing dosage to 0.36 mg kg⁻¹, and in the case of later applications up to 0.43 mg kg⁻¹. Less CCC residues were observed in times of high precipitation or intensive irrigation. However, the permitted maximum concentration of 5 mg kg⁻¹ CCC residues in the grain was by far not reached.