When using herbicides, there are two main factors that must be carefully considered: dosage and timing. The pesticide information network Xiaobian has focused on these two key aspects to provide a detailed explanation for everyone.
Chemical control involves determining the sensitivity of pests and crops to a specific herbicide. The goal is to apply a dose that effectively controls or eliminates the weeds without harming the crop's normal growth. The greater the difference between the crop and the weed, the more flexibility there is in choosing the type and concentration of the herbicide. In contrast, pesticides used against insects or fungi must be carefully selected because they target different biological groups—pesticides for animals versus those for plants, and bactericides for fungi. These differences in biology make it essential to use the correct dosage. However, with herbicides, both crops and weeds are plants, sometimes even from the same family, like wheat fields where wild oats (from the Poaceae family) are present. This makes it necessary to use high concentrations of herbicides, often at very precise levels.
The effective dose per unit area is critical. For insecticides and bactericides, concentration is usually the main concern, but for herbicides, the balance between effectiveness on weeds and safety for crops is crucial. If the dose is too low, the weeds won’t be controlled; if it’s too high, the crop might suffer. When applying herbicides manually, accuracy is important, and when using motorized sprayers, uneven spray distribution due to nozzle issues can lead to missed areas or over-application.
Additionally, weeds and crops often compete for the same resources, and their growth stages are similar. This means that the timing of herbicide application is limited. For example, pre-emergence herbicides like pendimethalin or acetochlor need to be applied before the weeds have emerged, typically just before or after planting. Once weeds start growing, reapplication may not only be ineffective but could also damage the crop. Therefore, careful planning of farming activities such as sowing, fertilizing, and spraying is essential to ensure proper timing.
Herbicides applied to leaves and stems also require specific timing. For instance, nicosulfuron in corn fields works best when applied during the 3-5 leaf stage of corn and the 2-4 leaf stage of annual weeds, or around 5 cm in height. Applying it too early or too late reduces its effectiveness, as young weeds absorb less, while older ones develop resistance. Drought conditions can further reduce the herbicidal effect by delaying weed emergence.
In conclusion, the scientific and rational use of herbicides is essential for optimal results. Paying attention to dosage and timing ensures better control of weeds while protecting the crop. Ignoring these factors can significantly reduce the effectiveness of the treatment and may lead to long-term problems in the field.
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