The potential uses for Napier Grass (Pennisetum purpureum) continue to grow as researchers have been testing certain areas of agribusiness with it. We have already seen how the use of the grass around old mining sites can help to decontaminate the polluted ground and know that its use as a biomass fuel is a possibility that is also being explored. Now researchers have been testing the possibility of using the grass as a “trap plant” to protect crops from pest damage.
This process is currently in use for maize crops in Kenya and the process has been detailed in a document that was jointly released by the International Centre of Insect Physiology and Ecology (ICIPE), Kenya Agricultural Research Institute (KARI), Ministry of Agriculture, Kenya, Ministry of Livestock Development & Fisheries, Kenya, Rothamsted Research, UK. The process is referred to as the Push-Pull Field Strategy and is used to control the gramineous spotted stemborer.
The way it works is that the Napier grass is planted in a border around the maize crop in such a way that it will pull the stemborer moth away from the maize. After the stemborers lay their eggs on the Napier grass the larvae are unable to develop into adults on the grass. Also in the crop desmodium is planted between the rows of maize. The rows of desmodium serve three useful purposes, the first is that they repel the stemborer moths who do not like the smell, the second is that it improves the fertility of the soil and the third is that the presence of the desmodium stops the growth of striga weed.
The reason why luring the stem borer moth to the Napier grass where it will lay its eggs is because it has been found that the even though the moth prefers to lay its eggs on Napier grass it has proven to be an unsuitable host for the larvae. The mortality rate of the larvae hatched on Napier grass is extremely high, even when a more suitable host such as a crop of maize is nearby.
In effect, the presence of Napier grass around a field of maize provides both an insecticide solution and a herbicide solution to enhance the field’s yield.
All of this sounds very promising and is one of a number of ways in which trap crops are being used to improve agricultural conditions. There is, however, one note of concern and it involves the health of the Napier grass plant in eastern Africa. A stunting disease of Napier grass has been spreading, affecting the growth of the grass.
According to one source “The Napier stunt disease is caused by 16SrIII group of phytoplasma, specialised wall-less bacteria that are obligate parasites of plant phloem tissue. The vectors of phytoplasma in Napier grass are not yet known. Therefore, there is an urgent need to identify vector(s) of Napier phytoplasma so that a regional resistance screening programme could be established.”
It means that resistant grass varieties must be found that can be used in place of those that are affected by the disease. Failure to do so will threaten the Push-Pull Systems already in place as well as threaten the milk production as livestock lose a significant food source.