Seven major considerations for the use of bispyrib ether
Bispyribac-sodium is an effective herbicide used in rice fields to control weeds, including most broadleaf weeds, some sedge species, and valerian, which are resistant to other herbicides. When applying bispyribac-sodium, it’s essential to pay attention to seven key factors to ensure both effectiveness and safety.
First, strictly control the application timing and dosage. Due to its high activity, the application window must be precise. For indica and japonica rice varieties, it should be applied after the 5-leaf stage. Some manufacturers claim that adding succinic ether allows for use at the 3-leaf stage, but this method lacks sufficient scientific validation. After the 5-leaf stage, rice plants have a stronger ability to metabolize the herbicide, improving safety. The recommended dose is typically 20–30 mL per 100 L of water. However, in areas where resistance has developed, dosages may increase to 30–40 mL. Always conduct small-scale tests before large-scale application to avoid overuse.
Second, be aware of the selectivity differences between rice varieties. The safety of bispyribac-sodium varies depending on the type of rice and leaf stage, mainly due to differences in the metabolic enzyme GST. Indica, hybrid, and japonica rice show increasing sensitivity to the herbicide. Chlorosis may occur after application, especially if applied too early or under stressful conditions like temperature fluctuations or weak seedlings. In most cases, symptoms resolve within 10–15 days. Adjust the dosage and timing based on local rice varieties for best results.
Third, monitor temperature changes. The ideal temperature range for application is between 15°C and 35°C. Within this range, the herbicide becomes more effective as temperatures rise. Below 15°C, performance becomes unreliable, and the risk of phytotoxicity increases. Above 35°C, there is also a higher chance of damage. In southern regions, such as the Yangtze River basin, temperature fluctuations during early rice planting require extra caution.
Fourth, be cautious about resistance to quinclorac. Prolonged use of bispyribac-sodium and quinclorac can lead to resistance in weeds like valerian. This means that in some areas, the herbicide may not perform as expected. It's important to remain cautious and consider rotating herbicides to prevent resistance buildup.
Fifth, follow the “drain, apply, re-water†principle. Before application, drain the field to expose weeds and keep the soil moist. After treatment, re-water the field and maintain a shallow water layer for 7 days. This practice significantly improves herbicide efficacy. Additionally, applying the herbicide in dry conditions is safer than in flooded or transplanted fields, so managing water levels is crucial.
Sixth, take into account the effect of environmental pH on herbicide performance. Lower pH levels increase the degradation rate of bispyribac-sodium. Fertilizers like potassium dihydrogen phosphate can lower pH and reduce herbicide stability, while urea and ammonium bicarbonate, being alkaline, can extend the herbicide’s effectiveness. Soil organic matter content also affects degradation rates, so understanding local soil conditions is important.
Lastly, understand the short-term impact on ALS activity. At reasonable doses, bispyribac-sodium does not inhibit ALS in indica rice after the 5-leaf stage. Any inhibition peaks around day 5 and disappears by day 9. Although yellowing and chlorosis may appear within 3 days, recovery usually occurs within 10–15 days. This temporary effect does not affect final yield, but proper interpretation is necessary for first-time users.
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