In recent years, the effectiveness of herbicides in corn fields has been disappointing, and some farmers have started to criticize their use. In response to these concerns, the author conducted research and shared several key insights.
First, the issue lies with the herbicides themselves. Due to intense market competition, many manufacturers have resorted to price cuts and aggressive advertising campaigns. However, this has led to increased production costs, and to maintain profitability, some companies have reduced the concentration or volume of active ingredients. For example, previously, a 500-gram bottle of herbicide could cover three acres effectively. Now, many products come in 300-gram bottles with lower active ingredient content, covering only two acres, and often at insufficient doses.
Second, weather conditions play a major role. Three main issues arise: high temperatures and drought during application. After planting corn, if there's little rain, dry and hot conditions can severely reduce herbicide effectiveness. Even if water is applied, it evaporates quickly, reducing the herbicide’s impact—this was notably seen in 1998. The second issue is excessive rainfall after application. Sudden or prolonged rain can wash away the protective layer of the herbicide, leading to loss of effectiveness. Weeds and their roots may not absorb enough to be killed, resulting in poor control. Third, heavy rain in the mid to late growing season can disrupt the timing of weed germination. Soil-applied herbicides are effective for about 45–60 days, but if there’s too much rain, new weeds emerge, creating a "no grass early, lots of grass later" situation—commonly observed in 2003.
Third, improper application methods also contribute to the problem. Many fields have excessive crop residue from wheat harvesting, which reduces the contact area between the herbicide and the soil. Some farmers apply only 1–2 sprayers of water per acre, leading to uneven coverage and reduced effectiveness. Additionally, applying herbicides too late, when weeds are already large, is another issue. If the field is already covered in weeds or has mature grass, the herbicide may not work effectively, especially on monocots with more than three leaves.
To address these challenges, the author suggests several strategies. First, choose high-quality herbicides from reputable brands with high active ingredient concentrations, such as 48% Zhongdian Caoba (CLP Group), 50% Xinyu Steam (Xuanhua), 48% Dingyi, or 42% cyantriazine. For fields with heavy residue, the “double increase one mix†method has proven effective. This involves increasing both water usage (2–3 sprayers per mu) and dosage by 30–50% to compensate for the residue and prevent volatilization. The “one mix†part refers to combining two different herbicides with non-overlapping active ingredients, such as 48% Zhongdian Caoba + 40% Propyramid, or 50% Xinyu Steam + 42% Cyanide B. Each should be used at 65–75% of the recommended dose to avoid phytotoxicity while enhancing control. Finally, for fields with large weeds, applying 600–800g of glyphosate before spraying can help eliminate existing weeds effectively.
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