Weeds are undesirable in agriculture activities since they compete with food crops for available soil nutrients, air, water, sunlight and space. Reports indicate that when these herbicides are applied, only about 1% is effective whereas the remaining 99% exist as residues in the surroundings thus posing serious threats to human health, the environment, wildlife and other non-target organisms. The objective of this work was to determine the level of some herbicide residues in sweetpotato. The sweetpotatoes were cultivated in a completely randomized block design (CRBD) with four replications at the Crops Research Institute Agronomy fields, Kwadaso where different treatments made up of combinations of five (5) pre-emergence herbicides (butachlor [50g/L-3L/Ha], imazethapyr [240g/L-3L/Ha], metolachlor [333g/L-4L/Ha], pendimethalin [500g/L-3L/Ha] and terbutryn [167g/L-4L/Ha]) and one (1) post-emergence herbicide (propaquizafop [100g/L-1.2L/Ha]) were applied and a control which involved strictly hoeing. After harvest, samples were randomly selected and extracted using a modified QuEChERS extraction method followed by Liquid Chromatography-Mass Spectrometry (LC-MS) to determine the residual levels of the herbicides. The results showed that sweetpotato samples from the control (field work which was strictly hoeing as the method of weed management) had no residues detected. Butachlor, imazethapyr, terbutryn and propaquizafop were also not detected in their respective sweetpotato samples analysed. However, pendimethalin and metolachlor residues were detected at concentrations of 0.0023 µg/g and 0.0029 µg/g, respectively. The findings suggest that herbicide residue levels detected in this study were considerably lower than the maximum acceptable limit (0.05 mg/kg) and thus the dietary exposure could be considered safe to humans.

1.1 Background
Sweetpotato (Ipomoea batatas L.) is a very vital food and industrial crop, cultivated globally with an annual production of over 122 million metric tonnes (Ofori et al., 2009). According to Milind et al. (2015), sweetpotato cultivation dates back to the 750 BC, thus one of the oldest vegetables known to mankind. Several species have been commonly used in religious rituals, medicinal and ornamental purposes. It is known to be a staple starchy and tuberous root vegetable and its production is increasing rapidly in many countries in the Sub-Saharan Africa (Korada et al., 2010). According to Amengor et al. (2016), Saharan-Africa has about 13.37 million hectares of land cultivated with sweetpotato, thus making it the third most important root crop after cassava and yam. Here in Ghana, sweetpotato is a major non-traditional export crop and in the year 2013, the harvested area was about 74,000 hectares (FAOSTAT, 2015). Odebode et al. (2008) attributed the wide spread of sweetpotato in Africa to its ease of cultivation, high ability to tolerate drought and hence its capacity to withstand the rather harsh environmental conditions characteristic of this agro-ecological zone. Other factors that have contributed to the widespread cultivation of this food crop includes the low requirement for fertilizers and the flexible planting and harvesting periods. The white or yellow–fleshed sweetpotato are the commonly grown varieties in most parts of Africa, including Ghana (Kapinga et al. 2001). The orange-fleshed cultivars in particular have been reported to possess a high content of naturally bio-available precursors of vitamin A (β-carotene) and its cultivation is therefore encouraged in the developing countries due to their prominence in combating vitamin A deficiency (Laurie et al., 2015). Furthermore, properties such as anti-carcinogenic, cardio-vascular disease-preventing and its high nutrient content has resulted in its recognition as a health food (Njintang et al., 2016). A report by Ofori et al. (2009) showed that sweet potato is not usually integrated into the menu of most food service establishments and even in the household menu, and this is probably because more importance and uses are attached to the other roots crops such as cocoyam, cassava and yam (Adu-Kwarteng et al., 2002; Opare-Obisaw et al., 2000).

Degras (2003) reported that, 57% of food crops in some parts of Africa are lost due to the presence of weeds, hence the need to effectively apply herbicides. Weeds influence agricultural activities by competing with crops for available soil nutrients, air, water, sunlight and space, and also harbouring other invasive pests (Wyss and Müller-Schärer, 2001). In modern times, agrochemicals form an integral part of agricultural production systems globally. Herbicides are described as a subtype of pesticides which are applied with the intention of killing, controlling or preventing the excessive growth of weeds or unwanted plants. The control of weeds with herbicides in modern day agriculture has become indispensable due to the acute shortage of farm labourers (Ponnusamy et al., 2015). Dinham (2003) estimated that about 87% of Ghanaian farmers apply pesticides to control pests, diseases and weeds during the cultivation of fruits and vegetables. Ntow et al. (2006) reported that out of the pesticides used in Ghana, herbicides make up 44%, 33% for insecticides and 23% are fungicides. Due to the chemical nature of herbicides, using them excessively and repeatedly may result in serious problems including phytotoxicity to food crops, residual effects on susceptible crops, adverse effects on non-target organisms and ultimately severe health hazards to human and animals due to the accumulation of residues in the crops, soil, surface and ground water (Ponnusamy et al., 2015). Furthermore, upon the realization of the effectiveness of these herbicides, farmers tend to increase application consistently to meet their production targets without taking into consideration the negative aspects associated with these herbicides. According to Das and Mondal (2014), the improper use of these chemicals can injure food crops, severely damage the environment and also pose health threats to the applicator as well as other people exposed to the chemicals.

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Item Type: Ghanaian Topic  |  Size: 85 pages  |  Chapters: 1-5
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