Post by Emily Guevara-Heredia on behalf of Replenish
Edited by Jo Milton
What is biodiversity?
To understand this word, it’s a good idea to begin with an exercise. First, I want you to remember the last time you were at a city park and the life forms you watched there. Are there any animals? How many plants can you identify? Now, imagine the last time you were at a Country or National Park and do the same. Do you see different animals, plants and other living organisms? In each location you can see one or other type of organism, but they vary. This variety is called ‘biodiversity’, and it is important because all organisms have direct and indirect interactions.
Pest control
Commonly, when people think about pest control, the first thing that comes to their mind is pesticides. These products are typically chemical compounds that can cause soil, water and air pollution, as well as be harmful to wildlife. Other pesticides, with potentially less risk of contamination, may be used by organic farmers.
The role of natural enemies
Indeed, organic farmers use the above mentioned pest control options, but only when other ones do not work. What are these other options? One answer is biological control methods. These can involve the use of living organisms to solve the pest problem, such as insects, arthropods and nematodes.
If we examine their role within their usual habitats, natural enemies interact with other organisms and preserve the equilibrium. To expand on this, imagine a plague of mosquitoes, continually reproducing and multiplying. How can we control it? Well, the reason why this is not a frequent occurrence is because of natural enemies, such as insectivorous birds, who eat the mosquitos. Natural predators help to control the numbers of prey species, and this has been happening for hundreds of thousands of years.
An example that we benefit from as gardeners is ladybirds eating greenfly and blackfly, also known as aphids. You can even buy ladybirds or their larvae to help control your aphid numbers. Better still, naturally encourage ladybirds by leaving a patch of nettles, plant flat-topped flowers like yarrow, fennel and dill, and avoid using pesticides.
DAVID S. FERRY III from PLANT CITY,FL., U.S.A., CC0, via Wikimedia Commons
The role of plants
There are also options that involve the use of plants to combat pests. By ‘companion planting’ specific species around your ‘target crop’, you can attract the natural enemies of the pest using ‘haven plants’, or even repel certain pests.
Many strongly scented plants will deter some insects. For example, chives, onions and garlic can help reduce carrot fly, whereas dill and marigolds may discourage aphids. Aromatic plants like herbs can also be used to confuse pests. The theory is that they can’t detect the smell of the ‘target crop’ as easily when there are lots of other scents in the air.
Chiswick Chap, CC BY-SA 4.0, via Wikimedia Commons
You could try ‘trap crops’, which are sacrificial plants that attract the pests away from your crop. An example is planting nasturtiums around your broad beans – hopefully the blackfly will prefer to snack on them and your beans will be ignored.
Legumes, like beans, peas and clover, fix nitrogen in root nodules and while much of the nitrogen will be used by the legume plants themselves, some may be available in the soil for neighbouring plants. ‘Screening crops’ can also be used to stop pests from seeing the ‘target crops’.
Use of native plants
Today many of the plants used in pest control are not originally from the country where people are using them. Native plant species can help with local crops because they are able to attract the natural enemies of some of the main pests.
Recent agroecology studies have focused on ancestral and indigenous knowledge, because these communities have a long history of using ecologically friendly methods of pest control. The ‘three sisters’ method is an ancient example of a companion planting technique where sweetcorn, beans and squash are grown together. Read more on this in the Replenish ‘growing food in small spaces’ blog.
Why increasing plant biodiversity is important for pest control
To conclude with this topic, I’ll summarise the importance of expanding plant biodiversity for pest control. Firstly, major diversity can have a positive impact by encouraging different types of natural rivals, as well as predators into the same area as the crops. Secondly, when there are various plant species they may support nutrient fixation within the soil, which will improve the growing conditions. Finally, there is an ecological benefit for native species by prioritising them and ensuring their continued existence.
As you see, the power of biodiversity can have a positive impact on crops. Natural pest control can save money and allows land used to grow food to also provide an ideal habitat for wildlife to live and thrive. Additionally, it’s helpful to remember that ancestral knowledge can provide a key to applying these methods. The ultimate goal is to find balance between humans and nature, something that needs to be taken into account for a better future for all.
Want more tips? Check out our other grow-your-own guides
Replenish 
.jpg){kind=link}
