**8. Effect of post-emergence herbicides on weed control in maize**

Application of herbicides after the emergence of maize and weed are wellknown as post-emergence herbicides. Generally, post-emergence herbicides spray/ apply in standing crop targeting weeds canopy by using the sprayer equipment.

The most popular/well-known herbicides which have been found to be effective when applied as a post-emergence for effectively control of weeds in CA-based maize system are Atrazine, Tembotrione (Laudis), Halosulfuron methyl (Sempra), Tembotrione (Laudis) + Atrazine, Halosulfuron methyl (Sempra) + Atrazine [58]. Earlier findings [62] revealed that pre-emergence herbicides pendimethalin and atrazine reduced the grassy and broadleaves weed population to a significant extent and among the pre-emergence herbicides, later (atrazine) resulted in a higher reduction in grass weed population at the early stage (20 days after seeding) than former (pendimethalin). But further he suggested, the post-emergence herbicides, the mixture of tembotrione + atrazine was more effective in controlling all classes of weed flora at 40 and 60 DAS. Tembotrione alone also showed good control of grasses and broad-leaved weeds. Atrazine as pre-emergence followed by (fb) tembotrione + atrazine as post-emergence found best combination and this combination reduced the weed dry matter to the tune of 98.7 and 97.9% at 40 and 60 DAS, respectively which ultimately resulted in significantly higher grain yields (11.57 t ha<sup>−</sup><sup>1</sup> ) with maximum net returns.

However, when a single herbicide is used for a long time for controlling the same weeds it may create resistance against the specific weed(s). Therefore, long term basis continuous use of the same herbicide should be avoided. So, it should be rotated with the use of multiple herbicides with a different mode of action to avoid/ delay weed resistance against specific weeds.

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*Chemical Weed Management in Maize (*Zea mays *L.) under Conservation Agricultural Systems…*

Scientists found that application of two or more compatible herbicides use as a tank mixture are more effective to control broaden the spectrum of weeds including grasses, broadleaves, and sedges than a single application [11, 63]. In the USA, Atrazine has been used since 1958 in several million hectares of maize field due to its low cost, control of a broad spectrum of broadleaf weeds, flexible application timing, and also can be used as both pre- and post-emergence in combination with several other herbicides. As a result of long-term and continuous use, the atrazine was found in accumulation in food products, groundwater, and aquatic systems [64]. Therefore, we should be careful to know the residual effect of applied herbi-

**9. Precautionary measures during application of herbicides in the** 

risk to exposed workers if precaution measures are not properly followed.

With the use of herbicides, there is a certain risk of intoxication to directly exposed environment, food product, workers, as well as applied crops, since it depends on numerous factors. Therefore, before application of any herbicide, its short and long term toxicity/risk factors should be considered. The risk of worker intoxication with pesticides and herbicides, depends on several factors as how they will be handled and used. It can be grouped under two major factors; the toxicity of the respective herbicide and how it was exposed under specific working condition [66]. Therefore, it is an important to must follow the safety and health management guidelines while working and using the herbicide at all steps as set out by the industrial hygiene [67]. The steps are the ability to antedate, identify, diagnose, evaluate, and minimize the risks in the workplace. Therefore, the Preventive safety measures of worker(s)/personnel such as psychological measures; administrative: legislation, standards, and procedures; and hygiene, cleaning, maintenance, and safety of the environment also important during selection and application of pesticides [68].

From the above discussion of the chapter, it is confirmed that weeds are the major challenge in CA crop production systems, where almost 16 to 42% yield reduction is occurred due to weed infestation and one-third of the total cost of cultivation is spent on weeding. On an average of 13.1% of crop reproduced is actually lost in the farmers' fields even after adopting in traditional weed control. The zero/strip-tilled/permanent beds or till the soil with fresh beds based crops production system is an alternate option through mechanized precision planting within a single pass. Although, the CA-based crop management techniques will be faced the major concern of weed management initially. Therefore, proper weed management

Herbicides are chemical compounds used to control weed species but could also phytotoxic to crops and harmful to animals through entering direct or indirect in food chain. Therefore, herbicides should be carefully selected considering the toxicity, residual persistence in soil and water bodies as well as cropping systems. The herbicide residual persistence can be affected the succeeding crops in a crop rotations and also the runoff of rain water from crop fields to water bodies which may cause the lethal and hazardous to water organism and human beings [65]. However, non-target living organisms that come to direct contact with weedicides can be harmful or poisonous especially if they have carry the chemical of the toxic action [66]. Therefore, while working with herbicides poses an always chemical poisoning

*DOI: http://dx.doi.org/10.5772/intechopen.89030*

**crop field**

cides when using the as short term as well as long term.

**10. Conclusion and policy implication**

*Chemical Weed Management in Maize (*Zea mays *L.) under Conservation Agricultural Systems… DOI: http://dx.doi.org/10.5772/intechopen.89030*

Scientists found that application of two or more compatible herbicides use as a tank mixture are more effective to control broaden the spectrum of weeds including grasses, broadleaves, and sedges than a single application [11, 63]. In the USA, Atrazine has been used since 1958 in several million hectares of maize field due to its low cost, control of a broad spectrum of broadleaf weeds, flexible application timing, and also can be used as both pre- and post-emergence in combination with several other herbicides. As a result of long-term and continuous use, the atrazine was found in accumulation in food products, groundwater, and aquatic systems [64]. Therefore, we should be careful to know the residual effect of applied herbicides when using the as short term as well as long term.
