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Live rice paddy field except for heavy seeding
In direct-seeded rice fields, weeds emerge early and in large quantities, with multiple peaks of weed growth. The first major peak occurs 5–7 days after sowing, dominated by barnyardgrass and waterhemp, which account for about 70% of total weed biomass. This makes it crucial to focus on soil closure before the rice seedlings emerge. The "one-time herbicide application, two-time follow-up, three-time supplementary elimination" method is most effective when targeting the early stages of weed growth.
Weed occurrence patterns vary depending on whether the rice is sown in wet or dry conditions. In wet direct-seeding fields, the first peak appears 5–7 days after sowing, dominated by grasses like barnyardgrass and waterhemp. The second peak occurs around 15–20 days later, featuring sedges, broadleaf weeds, and other species. A third peak arises between 20–30 days, mainly consisting of grasses. Dry direct-seeding fields show similar patterns but include additional weeds such as crabgrass, ironweed, and waterpepper.
Soil-closure herbicides applied before the rice emerges are highly effective in preventing a majority of weeds. Commonly used herbicides include pretilachlor, butachlor, pendimethalin (Shi Tianbu), and oxadiazon, which target grassy weeds. For broadleaf weeds and sedges, bensulfuron-methyl and pyrazosulfuron-methyl are recommended. Mixing different herbicides can enhance coverage and reduce resistance risk. Commercial formulations like Xinye (dioxin EC) and Quick Removal (benzyl dipropene) offer convenience and efficiency.
In dry rice fields, herbicides like Shi Tianbu and Dingye EC are often applied after seed soaking and before germination. It's important to maintain soil moisture for 5–7 days post-application without standing water. After rain, proper drainage should be ensured to avoid phytotoxicity and damage to rice seedlings.
For paddy fields, herbicides such as pretilachlor and its combinations are used after seed germination. Due to long-term use of butachlor, resistance has developed against certain weeds, so combining it with other agents like bupropion and ketoxime improves control. In fields with high dry gold and grass infestations, herbicides like Shi Tianbu and pretilachlor are effective. When soil is too dry for timely closure, propionamide-based herbicides can be used during the early seedling stage.
Stem-and-leaf herbicides are used as a secondary measure to manage remaining weeds and control the second peak. For grass-dominated fields, quinclorac is effective when applied at the two-leaf stage, with a 3–5 cm water layer maintained for 5–7 days. Dosage should not exceed 25 g per mu to prevent damage. If resistance is present, alternatives like Origen or Han Lesheng can be used with increased dosages.
Waterhemp-dominated fields benefit from applying a daughter’s milk herbicide after the first leaf stage, followed by a water layer two days later. Broadleaf weeds require careful application of bensulfuron-methyl or 2,4-D, with applications spaced 5–7 days apart. For older or resistant weeds, Weiba (6.9% emulsion) can be used, with specific dosages based on rice type.
In fields with broadleaf weeds and sedges, herbicides like ethoxysulfuron, thiazolone, and 2,4-D are effective. These should be applied after the fourth leaf stage to avoid toxicity. Additional stem-and-leaf treatments may be needed if weeds persist, depending on the field composition. Proper timing and application techniques are essential for optimal weed control and crop safety.