Chemicals (isoflavones) secreted by desmodium roots inhibit attachment to stiga to maize roots and cause suicidal germination of striga seed in soil
In the push-pull strategy 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 such as
4'',5''-dihydro-5,2',4'-trihydroxy-5''-isopropenylfurano-(2'',3'';7,6)-isoflavanone,
which stimulate striga seed germination and others such as
4'',5''-dihydro-2'-methoxy-5,4'-dihydroxy-5''-isopropenylfurano-(2'',3'';7,6)-isoflavanone
(suicidal germination) which inhibit their attachment to
maize roots, thereby reducing Striga seed bank. The legume
also improves soil fertility through nitrogen fixation.
Both Napier and desmodium plants provide quality fodder for livestock.
Therefore, farmers using ‘push–pull’ technology for pest control not
only reap harvests of 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 as 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.