Protective plants instead of pesticides

Coriander kills insect pests in cabbage plantings in Bali

In modern agriculture, methods for controlling pests and plant parasites using various chemicals prevail. Earlier in the articles, we considered (article) alternative methods of maintaining the quality of the crop, based on a more environmentally friendly approach. Another such approach to controlling insect pests is the “natural enemies” method. 

The natural enemies of many insects are some plants that release chemically active substances called volatile, which repel pests. In order to protect cultivated plants with plant protectors, they are planted in the fields together, row by row – this method is called “polyculture”. Polyculture, or mixed cropping, is commonly practiced by small-scale farmers in the tropics to ensure food security, optimal use of soil, labor and space, maintenance of soil fertility, erosion control, and to reduce the need for weed control. Mixed cropping is often associated with insect pest control.

Polyculture example 

This study evaluated the feasibility of using coriander polyculture in cabbage fields to protect against Diamondback moth, one of the most important pests, in the central highlands of Bali, Indonesia. Cabbage and coriander were planted through a row with a distance of 45 cm, the number of pests was calculated and compared with the field, where the sprout was only cabbage.

As a result of the experiment, it was found that the number of Diamondback moth at the larval and pupal stages, as well as the total density of larvae and pupae, were significantly lower in areas of mixed seeding than in areas of monoculture. In addition to the hypothesis about the release of chemicals expressed above, there are a number of alternative assumptions about how plants – natural enemies of insects can protect cultivated plants from them. 

For example, one of the hypotheses says that plant protectors do not scare away insects – pests, but only mask the smell of cultivated plants of interest to them. Another, more sophisticated hypothesis is that plants – defenders with their smell attract any other natural enemies of insects, for example field slug, which, when settled in polycultures, destroys and repels the Diamondback moth. Finally, a simpler hypothesis is that it is simply more difficult for insect pests in polyculture to find the plant of interest to them, since the planting area is halved.

Regardless of which of the hypotheses is the most true (and most often several of them are more or less true), the practical implication of our study is that mixed cropping of coriander, a valuable cash crop in the region, could allow effective Diamondback moth control with lower amounts of chemicals. Hence, cabbage/coriander mixed cropping together with Napier grass border crops fit in well with local cropping practices, and can be a feasible option in the highlands of Bali.

Full Text:

Adati, T., Susila, W., Sumiartha, K., Sudiarta, P., Toriumi, W., Kawazu, K., & Koji, S. (2011). Effects of mixed cropping on population densities and parasitism rates of the diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae). Applied entomology and zoology, 46(2), 247-253.