Controlling Stemborers and Striga Weed In Cereal Crops

  Stemborer Larvae                                                           Stemborer Moth                                      Striga Weed

Dr Zeyaur Khan, the leader of the Habitat Management Programme at ICIPE, says that both domestic and wild grasses, often ploughed under in modern monocropping practice, can help protect the maize by attracting and trapping the stemborers. The grasses are planted in a border around the maize fields, where invading adult moths become attracted to chemical emitted by the grasses them selves. Instead of landing on the maize plants, the insects head for what appears to be a tastier meal. These grasses provide the "pull" in the "push-pull" strategy. They also serve as a haven for the borers' natural enemies. Good trap crops include the well-known Napier Grass (Pennisetum purpureum), and Sudan grass (Sorghum Vulgare sudanese), a type of wild sorghum. Napier Grass has a particular clever way of defending itself against the pest onslaught: Once attacked by the a borer larva, it secretes a sticky substance that physically traps the pest and effectively limits its damage. The natural enemies lurking among the grasses go into action and dispatch the borers in both maize and grass host plants.

The "Push" in the intercropping scheme is provided by plants that emit chemicals (Kairomones) that repel the borers and drive them away from the maize main crop. The best candidates discovered so far for their borer-repelling properties are members of leguminous genus Desmodium spp.

Desmodium is planted in between the rows of maize. Being a low-growing plant, it does not interfere with maize growth, and furthermore has the advantage of maintaining soil stability and improving soil fertility through its nitrogen-fixing action. Desmodium is easy to harvest and serves as a highly nutritious animal feed. A ground cover of desmodium, interplanted  among the maize, reduces striga growth by a factor of 40.

Another plant, showing very good repellent properties, is molasses grass or Melinis minituflora. This is a "jack-of-all-trades" grass, as it is also a nutritious animal feed and repels tick to boot!

The  underlying chemical ecology of plant defense mechanisms are also being studied by the project. For instance, molasses grass release volatile chemicals that discourage stemborer adults from laying eggs, thus protecting nearby maize. Molasses grass also attracts natural enemies of stemborers which help in the defense. Current studies are focusing on the identity of chemicals produced by the roots of desmodium that are responsible for suppressing the striga weed. Whatever the strategy, stemborers and striga weed are now on the defensive when "push-pull" is at the battlefront.

      (Napier Grass)                               (Sudan Grass)                                   (Desmodium)                                (Molasses Grass)

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