Corn: when to apply soil herbicides and when to apply foliar herbicides?
In the post-war period, the exclusive use of agronomic and mechanical methods had a negative impact on the quality of corn yields. The introduction of herbicides containing dicamba and atrazine in the 1960s increased the profitability and area of cultivation. Currently, herbicides spreading from nicosulfuron are among the most popular for controlling weeds in corn. A breakthrough occurred in 2007, with the cessation of the use of atrazine due to its harmfulness to humans and environmental pollution.
Weed Control in Corn
The development of weed control technology in corn is an excellent example of the progression from agronomic methods to chemical weed control. The most popular products currently are nicosulfuron and dicamba herbicides. Unfortunately, atrazine has proven to be harmful to the environment and has permeated groundwater.
Crops like corn are characterised by their growth, development, and yield structure. It remains actively vegetative until the months of September and October. Usually, by the beginning of May, we can talk about the emergence of weeds, which significantly weaken its potential yield. The level of weed pressure in corn is largely determined by agronomic practices, the selection of cultivated plants, the weather conditions prevailing during the growing season, and the soil's ability to support the growth and development of weeds.
A thorough understanding of the effectiveness and safety of herbicide application, along with the timing of their applications, will help in preparing a herbicide treatment programme. The article discusses the most important weeds occurring in corn production, the conditions for seed germination, methods of their control at various developmental stages, as well as the influence of cover crops on weed infestation, chemical methods of weed control, soil-applied herbicides, and their impact on the environment (including specific toxicity), along with prevention of their infiltration into watercourses. The article also presents practical recommendations for minimizing the negative impact of herbicides used on weeds and non-crop plants.
How to Control Weeds in Corn?
The future of weed control in corn lies in solutions that combine the benefits of both contact and soil-applied herbicides, intended for use in early developmental phases - the most favourable period for the safety of this crop. For many years, farmers have used soil-applied fungicides (fungicides used in the soil). Atrazine provides selective weed control, but is also considered an environmental contaminant. Its main disadvantage is toxicity to humans and animals, as well as being washed away by water.
In the face of competition from weeds, the plant has two options - either strive to overcome them (above ground) or minimize their impact by strengthening underground. After the emergence of corn, the plant develops a root system and above-ground part. If the soil is weed-free, it concentrates its resources on developing a strong root system that allows for better absorption of moisture and nutrients. In the presence of weeds, the plant invests in the development of its above-ground part, which controls weed growth through shading. In this case, the plant incurs costs - the root system and yields are smaller. Weed control in corn is most effective in early developmental phases, before the appearance of 3-4 leaves. The best systems include soil-applied herbicides with a broad spectrum of action and products applied to the green parts for better control of black weeds.
Weeds can significantly reduce corn yields and cause considerable damage; this applies to all corn crops, including dwarf varieties. The harmful effects of weeds result not only from their competitiveness but also from a number of other factors. For example, common couch grass secretes a substance that limits the development of the root system, a phenomenon known as negative allelopathy. Trials conducted in demonstration plots in Golub-Dobrzyń have shown that the most effective protection is provided by herbicide treatments applied to corn crops in the early developmental phases. On the other hand, foliar herbicide treatments in later developmental phases should primarily have a corrective nature.
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