Imidazolinone herbicide dissipation in rice fields as affected by intermittent and continuous irrigation

Abstract

Background:

Clearfield^® (CL) rice is one of the most successful tools for selective weedy rice control, using imidazolinone herbicides (IMI). However, IMI have residual soil activity and may carryover to non-tolerant crops growing in succession. It is necessary to find options to reduce IMI persistence in paddy rice fields.

Objective:

Evaluate the effect of water management on IMI dissipation in rice paddy and its carryover to soybean and non-CL rice.

Methods:

The herbicide mixture of imazapyr and imazapic totalizing 147 g a.i. ha⁻¹ and 49 g a.i. ha⁻¹, respectively, was applied half in preemergence (S₃ stage – rice spike stage) and the other half in postemergence (V₃-V₄ rice stage). After herbicide application, a total of 21 samples were taken for analysis of residues. Soil samples were air dried and herbicides residues were analyzed using high-performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS).

Results:

Calculated field dissipation half-life (DT_½) of imazapyr was 182.5 and 42.0 days in continuous flooding and intermittent water management, respectively. Imazapic had a DT_½ of 96.3 days on intermittent water management. No adjustment for the dissipation regression parameters was obtained for imazapic in continuous water management. No reduction in yield components was observed in soybean when grown in soil with imidazolinone residues. On the other hand, non-CL rice showed decreased shoot dry weight and stem number.

Conclusion:

Imidazolinone herbicides have a longer half-life under continuous rice water management than intermittent. Therefore, growers can use intermittent irrigation in ares prone to IMI carryover and can use soybean in rotation.

Keywords
Residual; Imidazolinone half-life; Carryover; Soil residue