Weed Management Essay Example

by blocking sunlight. Additionally, cover crops help suppress the activity of parasitic plants by lowering soil temperature. Moreover, cultivars like rice are employed to outcompete weed plants and inhibit their growth. Lastly, sprays made from weed and plant extracts possessing herbicidal properties are applied on plants with damaging effects.

Biological controls in annual cropping systems are challenging due to factors such as difficulty in understanding the ecology of the targeted weed and limited options for biological control agents. It is important to note that biological controls do not completely eliminate weeds, but instead effectively manage their growth. Cultural methods play a significant role in weed management. For instance, selecting cultivars like wheat and rice that grow rapidly can outcompete weeds for nutrients, thereby restricting their growth. Additionally, these crops reach maturity before weeds establish themselves, minimizing their impact. Another effective cultural method is crop rotation, where plants with allelopathic properties are planted during the peak activity of targeted weeds. This method also prevents harmful parasitic weeds from affecting specific crops since they are cultivated during the dormant phase of weeds.

Plant spacing is an effective strategy to control weed growth. By keeping crops close together, sunlight is limited, leading to reduced chemical activity in weeds. This lack of nutrients and space results in the withering of weeds and inhibits the development of their root system. Another approach, multiple cropping, involves growing different crop varieties together. This practice has a significant impact on reducing weed infestation as each crop has an allelopathic effect on specific parasitic plants. Consequently, multi-cropping creates unfavorable conditions for various types of weeds.

Mowing is a method of controlling weeds by reducing the level of

infestation of a specific plant, regardless of its desirability. Essentially, a weed is any crop or plant that grows in an unwanted location. However, certain weeds are typically overlooked if their impact is minimal, such as small plants in a eucalyptus plantation. Similarly, grass is usually not classified as a weed but can become one if it surpasses its desired height. Mowing also helps manage other weeds that may grow alongside the grass. Since grass is not considered a crop, it is susceptible to most herbicides used for weed control.

Controlling weed growth on a lawn without harming the grass is challenging. Mowing is the only effective method, but it doesn't mean that the grass becomes a weed when it grows beyond the desired level. In fact, it provides favorable conditions for weed activity.

Mowing serves as a preventive measure against weed growth by preventing weeds from outgrowing grass. It reduces the conditions favorable for weed growth. One effective herbicide, Sulfonylurea, is used before planting, during pre-emergence and post-emergency periods of growth. It helps prevent the growth of Canada thistle and wild garlic in small grain plants, as well as controlling quackgrass and shattercane in corn. Herbicide selectivity is the ability of a herbicide to selectively kill weeds without damaging the companion plants they grow with. This selectivity is achieved through mechanisms like metabolism, where the desired crop species metabolize the herbicide into less harmful forms.

The herbicide is converted into a harmless compound and stored without affecting the plant's cell activity. The plant's defense mechanism triggers biochemical reactions that render the herbicide ineffective by breaking it down into non-toxic compounds.

Decomposition happens through various means,

such as the plant's ability to break down the herbicide, actions of micro-organisms, temperature changes causing chemical disintegration, and photodecomposition transforming the herbicide into crop-safe forms. Another process called adsorption transfers or transports the applied herbicide to soil regions with low plant cell activity.

Adsorption occurs when the herbicide becomes concentrated at the chemical barrier level, preventing germinating plants from being affected. This is also the case for plants with deep root systems, as the chemicals that concentrate near the surface are not absorbed by the plant. Additionally, adsorbed herbicide is inactive because it is not in solution form, making it unable to diffuse into plant cells. Soil applied herbicides are transported through translocation, with the chemical molecules diffusing through the epidermis into parenchyma cells.

The herbicide initially enters the xylem after passing through the endodermis layer. It then dissolves and spreads throughout the plant, reaching various parts such as leaves and shoots. When herbicides are applied to foliage, they dissolve in leaf phloem sugars. The high pressure within leaves pushes the solution through sieving plates into sinks, where it is actively transported into parenchyma cells. From there, it diffuses into stem xylem and is carried to cytoplasmic cells. Ultimately, it penetrates the cuticle and epidermis of root tips. Additionally, broomrapes (orobanche spp.) are parasitic plants that feed on most cereal plants.

The parasitic plant lacks chlorophyll and therefore cannot produce its own food. It relies on the vascular tissues of the host plant to obtain nutrients by attaching itself to the roots of the host. This attachment is made possible through a transfer organ known as the haustorium. The parasitic plant undergoes various stages of growth, including

periods of dormancy and active growth, and has the ability to rapidly evolve into different forms (Perez, Moreno and Rubiales, 133). To prevent its spread, resistant genotypes are being introduced into cultivated plants. However, a challenge arises from the fact that current cultivars lack resistance. As a solution, researchers are using wild relative plants in order to develop new genotypes. In addition, sandy soils have lower Cation Exchange Capacity (CEC), leading to a reduced binding of herbicide molecules to soil colloids.

As a result, a significant amount of the herbicide remains in the soil in its active solution form, which means that lower application rates are needed.