Polymeric Systems for the Delivery of Herbicides to Improve Weed Control Efficiency

*S. Marimuthu, P. Pavithran and G. Gowtham*

## **Abstract**

Weeds are unwanted plants, which interfere with the crop production. Weeds compete with crops for resources, causing severe yield loss. Chemical weed control through herbicides is a quite effective and reliable strategy to manage weeds. Herbicides constitute a major share of the global pesticide market. However, the applied herbicides undergo losses in the agroecosystem in different ways (chemical degradation, microbial decomposition, photo-degradation, leaching, run-off, and volatilization), thus lowering the herbicidal action coupled with contaminating ecosystem and groundwater. Encapsulation of herbicides is an innovative approach that addresses issues associated with the application of herbicides for controlling weeds. Encapsulation represents the embedding of an active ingredient in shell of polymeric material to achieve the controlled release of the active ingredient at the desired rate. The encapsulation of herbicides enhances stability, solubility, and bioactivity and alters the release pattern of herbicide resulting in improved weed control efficiency. Further, encapsulation lowers the application rate of herbicides, which in turn reduces the residue carryover of herbicide in soil and minimizes the environmental hazards. Therefore, encapsulated herbicide formulation has greater significance in the future weed management and will become ground-breaking technology in the chemical era of weed control.

**Keywords:** weeds, herbicides, polymers, encapsulation, weed control

## **1. Introduction**

Weeds are as old as agriculture that influence crop growth and yield. Weeds compete with crops for resources such as space, water, nutrients, and light, which indirectly affect crop growth. Weeds inflicted tremendous yield loss besides deteriorating crop and grain quality, chocking water flow in an irrigation channel, sheltering crop pests, and causing ailments in living beings. The estimate on yield reduction due to weeds was one-third among agricultural pests [1]. The average loss in agricultural production due to weed infestation were 5, 10, and 25% in most developed, developing, and least developing nations, respectively [2]. Weeds cause a yield reduction of 10–80% depending on crops, type of weed flora infested, and magnitude of crop-weed competition [3]. Generally, yield loss due to weeds is 37% in developing

countries, where either 90–95% or complete crop failure is common in certain locations [4]. There are 30,000 weed species infesting various crops on a global scale, out of which, 18,000 weed species are problematic causing severe yield losses in crop production. Estimates of 826 weed species were recorded in India, of which, 198 weed species were reported as serious weeds, while 80 weed species were classified as very serious weeds [5].

The degree of weed infestation is at an increasing rate in agricultural and non-cropped lands. The cost incurred for the adoption of weed control measures increases the cost of cultivation and reduces profit for the farmers. Manual weeding and mechanical weed management practices were the major options to manage weeds in agricultural fields. However, due to demand for human labor and increase in labor wages force the farmers to use herbicides to manage weeds. An annual average of 2 million tonnes of pesticides is consumed worldwide, where consumption of herbicides positioned first (47.5%) [6]. Herbicides are now widely used to manage weeds in modern agriculture. However, herbicides undergo various losses in soils after application *viz*. photo-degradation, volatilization, leaching, microbial degradation, run-off, etc., which in turn lowers the weed control potential of herbicides. Moreover, off-site transport of applied herbicides causes groundwater contamination. Nowadays, low volume herbicides are available, which show higher herbicidal activity and weed control efficiency over conventional herbicide formulations. Nevertheless, low volume herbicides are also reported with faster degradation potential in soil and increase the risk of environmental pollution. Therefore, encapsulation is an innovative and promising approach for developing controlled release formulations. Encapsulated formulation minimizes the herbicide loss in agroecosystem and improves weed control efficiency at a lower dosage. Encapsulation regulates the release and availability of active ingredients in the targeted site. Encapsulation involves the loading of active ingredients in the secondary material. The secondary materials are generally polymeric systems that regulate the release of active ingredients into the environment through diffusion-mediated process. Thus, encapsulation enhances the herbicidal activity and achieves higher weed control efficiency at a lower application rate. With the background, the chapter discusses the encapsulation of herbicides in the polymeric system and the characteristics of formulations and their scope in weed management.
