28 April 2020
A large part of sub-Saharan Africa depends on agriculture for its livelihood. However crops are threatened by pests and pathogens at all stages from the field to storage. It is reported that globally 20% - 40% of crop losses are caused by disease, pests and weeds. In a review, researchers from universities in Ethiopia, Rwanda, South Africa and Sweden have looked at the literature in relation to the use of botanicals as a means to protect and strengthen crops in Africa.
The review is focused on potato and tomato crops grown extensively in Africa where production has been hindered by several factors including low soil nutrients and poor agronomic practices. Major diseases impacting potatoes in Africa include blight, bacterial wilt and potato leaf role virus. Tomato crops can be wiped out by a pest called tomato leaf miner. Though native to South America, this pest has spread through Europe, the Middle East and, since 2006, has been found in parts of Africa.
Chemical fertilisers and pesticides play an essential role in decreasing yield loss, but indiscriminate use of these products can adversely impact human health and the environment. This can be more pronounced in developing countries where personal protective clothing and equipment are often poorly made and knowledge of safe practices can be limited. In addition, the high cost of importing chemicals and fertilisers means that these products are not an option for farmers in developing regions.
With this in mind, plant protection and plant strengthening methods which are environmentally friendly and economical are needed to fulfil the current and future food demand in Africa. Botanicals are defined as plant extracts, plant volatiles and natural oils which exhibit pest/pathogen control activities. Unlike synthetic pesticides botanicals are often less persistent in the environment as they can degrade rapidly making them less of a threat to the environment and human health. However, their low persistence and high degradability impacts the stability and shelf life of these products.
Botanicals have a number of modes of action against insects and pests, ranging from a simple repelling effect to direct toxicity by ingestion. Growth and reproduction inhibition are other ways in which botanicals can impact pests. Botanicals can also work as fungicides, creating an unfavourable environment for pathogens. The researchers stress that while many plant extracts would be excellent botanicals, some are toxic and carcinogenic to humans, animals and beneficial organisms. In addition most botanicals and plant strengtheners do not reach the effectiveness of conventional pesticides.
The researchers point out that while botanicals have a number of advantages and disadvantages, there is a need for more testing in the field. They suggest establishing a botanicals and plant strengtheners Africa network, possibly as a public-private-partnership. They cite an initiative called Plant Biologicals Network in Southern Scandinavia.
Journal of Integrative Agriculture DOI:10.1016/S2095-3119(19)62703-6