Chemicals (isoflavones) secreted by desmodium roots inhibit attachment to stiga to maize roots and cause suicidal germination of striga seed in soil
Desmodium produces volatile chemicals, such as (E)-ß-ocimene and (E)-4,8-dimethyl-1,3,7-nonatriene, which repel the stemborer moths from the maize ('push') while those released by Napier grass, such as octanal, nonanal, naphthalene, 4-allylanisole, eugenol and linalool, attract female moths ('pull') to lay eggs. Desmodium roots produce chemicals which stimulate Striga seed germination, such as 4'',5''-dihydro-5,2',4'-trihydroxy-5''-isopropenylfurano-(2'',3'';7,6)-isoflavanone, and others which inhibit their attachment to maize roots, such as 4'',5''-dihydro-2'-methoxy-5,4'-dihydroxy-5''-isopropenylfurano-(2'',3'';7,6)-isoflavanone (suicidal germination), thereby reducing Striga seed bank. The legume also improves soil fertility through nitrogen fixation.
Both plants provide quality fodder for livestock. Therefore, farmers using ‘push–pull’ technology for pest control not only reap three harvests (maize, Napier grass and desmodium); they also dramatically reduce the devastating effects of the parasitic weed Striga hermonthica through the effects of desmodium.
The grasses are planted in the border around the maize and sorghum fields where invading adult moths become attracted to chemicals emitted by the grasses themselves. Instead of landing on the maize or sorghum 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 well-known grasses such as Napier grass (Pennisetum purpureum) and Sudan grass (Sorghum vulgare sudanense). Napier grass has a particularly clever way of defending itself against the pest onslaught: once attacked by a borer larva, it secrets 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 or sorghum and grass hosts plants.