Miroslav Jursík

The risk of contamination by the acetyl‐CoA carboxylase inhibiting herbicides fluazifop‐P‐butyl and quizalofop‐P‐ethyl is significant, particularly in short‐season vegetables like spinach. This study examined meteorological factors affecting their efficacy and residue levels in spinach. Field trials were conducted in Prague, Czech Republic, in 2022 and 2023, using Echinochloa crus‐galli seeds at 150 seeds/m ² . Herbicides were applied at the four‐true‐leaf growth stage, with fluazifop‐P‐butyl at 110 g/ha and quizalofop‐P‐ethyl at 40 g/ha, under three irrigation regimes. Statistical analysis showed significant effects of temperature and irrigation on herbicide efficacy against E. crus‐galli and residue levels in spinach leaves. Fluazifop‐P‐butyl residues were approximately 10 times greater (287–480 μg/kg in 2022 and 76–91 μg/kg in 2023) than quizalofop‐P‐ethyl (25–42 μg/kg in 2022 and 5–9 μg/kg in 2023), even though its maximum residue level (MRL) is 10 times lower (20 μg/kg for fluazifop‐P‐butyl vs. 200 μg/kg for quizalofop‐P‐ethyl). Residues were notably higher in 2022 likely due to lower temperatures (mean temperature in the growing period 11.2°C), which slowed degradation of herbicides. Irrigation shortly after herbicide application (20 mm) reduced residue levels but decreased efficacy. Warmer conditions in 2023 enhanced efficacy, with a mean daily temperature of 6.3°C higher during the application‐to‐harvest period. Herbicide degradation was more temperature‐dependent than efficacy. Fluazifop‐P‐butyl is unsuitable for spinach due to the high risk of exceeding MRL values, while quizalofop‐P‐ethyl can be used safely under varied weather conditions without exceeding MRL.

In order to achieve integrated weed management, precision timing is just as important an aspect to consider as spatial precision: the stage of the plant at the time of action will impact its successful control or survivability and thus the selection pressure for herbicide resistance. Weed emergence models are one aspect of this precision timing, but they are yet underutilized. One critique has been that models based on bare ground emergence are not always validated with emergence in the crop, and yet also residual herbicides and their timing may also affect the model. In this work, we compare emergence of Echinochloa crus-galli on bare ground and in maize and the impact of early post-residual herbicides at several timings. Experiments on bare ground and in maize were set in Prague, Czech Republic, in 2021, 2022, and 2023. Bare-ground quadrats of 0.25 m² were randomly assigned in a space of 100 m². Maize plot treatments of four herbicides at each of five timings were assigned in a randomized complete block design (dimethenamid-P at 1008 g ai ha⁻¹, pethoxamid at 1200 g ai ha⁻¹, isoxaflutole at 96 g ai ha⁻¹, and mesotrione at 480 g ai ha⁻¹). Three 0.25 m² quadrats were enumerated in each plot from first emergence to full canopy closure (May to July). Model fit to emergence from the bare-ground plots using thermal time with a base temperature of 10 °C resulted in an AIC of −494. The bare-ground model was validated with emergence from the nontreated control plots in maize in 2022 and 2023, which accounted for over 85% of the variability in observed emergence. At canopy closure, total emergence since herbicide application was affected by herbicide and application timing. All herbicides at all timings reduced the emergence after application except for mesotrione. When beginning thermal time from the day of application, the emergence pattern after mesotrione application at all timings could be modeled with a single equation. E. crus-galli had a reliable emergence pattern within a local population; the predictive model created using bare-ground plots adequately predicted emergence in maize. This information can be used to time herbicides to coincide with the most effective moment in the flush in areas where E. crus-galli is the driver weed species.

Dynamics of herbicides degradation in carrot (Daucus carota L.) roots and leaves | Jaroslav Šuk, Kateřina Hamouzová, Jana Hajšlová, Miroslav Jursík | Agricultural Journals

(1) Background: Aryloxyphenoxy-propionates and cyclohexanediones are herbicides most widely used in dicot crops worldwide. The main objective of the study was to determine the dynamics of herbicide residues in carrot, lettuce, cauliflower, and onion in order to suggest a low level of residues in harvested vegetables. (2) Methods: Small plot field trials were carried out in four vegetables in the Czech Republic. The samples of vegetables were collected continuously during the growing season. Multiresidue methods for the determination of herbicide residues by LC-MS/MS were used. Non-linear models of degradation of individual herbicides in vegetables were calculated using the exponential decay formula. Action GAP pre-harvest intervals for the 25% and 50% maximum residue limit (MRL) and 10 µg kg⁻¹ limit (baby food) were established for all tested herbicides. (3) Results: The degradation dynamics of fluazifop in carrot, onion, and cauliflower was significantly slower compared to quizalofop and haloxyfop. The highest amount (2796 µg kg⁻¹) of fluazifop residues was detected in cauliflower 11 days after application. No residue of propaquizafop and cycloxydim was detected in any vegetable samples. (4) Conclusions: Aryloxyphenoxy-propionate herbicide (except propaquizafop) could contaminate vegetables easily, especially vegetables with a short growing season. Vegetables treated with fluazifop are not suitable for baby food. Lettuce and cauliflower treated by quizalofop are not suitable for baby food, but in onion and carrot, quizalofop could be used. Propaquizafop and cycloxydim are prospective herbicides for non-residual (baby food) vegetable production.