The push–pull technology is a strategy for controlling agricultural
pests by using repellent "push" plants and trap "pull" plants. For
example, cereal crops like maize or sorghum are often infested by stem
borers. Grasses planted around the perimeter of the crop attract and
trap the pests, whereas other plants, like Desmodium, planted between
the rows of maize repel the pests and control the parasitic plant
Striga. Push–pull technology was developed at the International
Centre of Insect Physiology and Ecology (ICIPE) in Kenya in
collaboration with Rothamsted Research, UK  and national partners.
1 The pull
2 The push
3 How push–pull works
4 See also
6 External links
The approach relies on a combination of companion crops to be planted
around and among maize or sorghum. Both domestic and wild grasses can
help to protect the crops by attracting and trapping the stemborers.
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 effective way of defending itself against the
pests: once attacked by a borer larva, it secretes a sticky substance
which physically traps the pest and limits its damage.
The "push" in the intercropping scheme is provided by the plants that
emit chemicals (kairomones) which repel stemborer moths and drive them
away from the main crop (maize or sorghum). The best candidates
discovered so far with the repellent properties are species of
leguminous genus Desmodium.
Desmodium is planted in between the rows
of maize or sorghum. Being a low-growing plant, it does not interfere
with the crops' growth and, furthermore, has the advantage of
maintaining soil stability, improving soil fertility through enhanced
soil organic matter content and nitrogen fixation. It also serves as a
highly nutritious animal feed and effectively suppresses striga weeds.
Another plant showing good repellent properties is molasses grass
(Melinis minutiflora), a nutritious animal feed with tick-repelling
and stemborer larval parasitoid attractive properties.
How push–pull works
This section does not cite any sources. Please help improve this
section by adding citations to reliable sources. Unsourced material
may be challenged and removed. (December 2011) (Learn how and when to
remove this template message)
The push–pull technology involves use of behaviour-modifying stimuli
to manipulate the distribution and abundance of stemborers and
beneficial insects for management of stemborer pests. It is based on
in-depth understanding of chemical ecology, agrobiodiversity,
plant-plant and insect-plant interactions, and involves intercropping
a cereal crop with a repellent intercrop such as
(silverleaf) (push), with an attractive trap plant such as Napier
grass (pull) planted as a border crop around this intercrop. Gravid
stemborer females are repelled from the main crop and are
simultaneously attracted to the trap crop.
Napier grass produces
significantly higher levels of attractive volatile compounds (green
leaf volatiles), cues used by gravid stemborer females to locate host
plants, than maize or sorghum. There is also an increase of
approximately 100-fold in the total amounts of these compounds
produced in the first hour of nightfall by
Napier grass (scotophase),
the period at which stemborer moths seek host plants for laying eggs,
causing the differential oviposition preference. However, many of the
stemborer larvae, about 80%, do not survive, as
Napier grass tissues
produce sticky sap in response to feeding by the larvae, which traps
them, causing their mortality. Legumes in the
(silverleaf, D. uncinatum and greenleaf, D. intortum), on the other
hand, produce repellent volatile chemicals that push away the
stemborer moths. These include (E)-β-ocimene and
(E)-4,8-dimethyl-1,3,7-nonatriene, semiochemicals produced during
damage to plants by herbivorous insects and are responsible for the
Desmodium to stemborers.
Desmodium also controls striga, resulting in significant yield
increases of about 2 tonnes/hectare (0.9 short tons per acre) per
cropping season. In the elucidation of the mechanisms of striga
suppression by D. uncinatum, it was found that, in addition to
benefits derived from increased availability of nitrogen and soil
shading, an allelopathic effect of the root exudates of the legume,
produced independently of the presence of striga, is responsible for
this dramatic reduction in an intercrop with maize. Presence of blends
of secondary metabolites with striga seed germination stimulatory,
and postgermination inhibitory,
(2′′,3′′;7,6)-isoflavanone, activities in the root exudates of
D. uncinatum which directly interferes with parasitism was observed.
This combination thus provides a novel means of in situ reduction of
the striga seed bank in the soil through efficient suicidal
germination even in the presence of grassy host plants in the
Desmodium species have also been evaluated and have
similar effects on stemborers and striga weed and are currently being
used as intercrops in maize, sorghum and millets.
Biological pest control
List of sustainable agriculture topics
List of companion plants
List of beneficial weeds
List of pest-repelling plants
^ Cook, Samantha M.; Khan, Zeyaur R.; Pickett, John A. (2007). "The
use of push-pull strategies in integrated pest management" (PDF).
Annual Review of Entomology. 52: 375–400.
doi:10.1146/annurev.ento.52.110405.091407. PMID 16968206.
^ Glover et al., Plant perennials to save Africa's soils, Nature 489,
359-361 (20 September 2012)
^ Khan, Z.R., Midega, C.A.O., Bruce, T.J.A., Hooper, A.M., Pickett,
J.A., 2010. Exploiting phytochemicals for developing a
‘push–pull’ crop protection strategy for cereal farmers in
Africa. Journal of Experimental Botany Volume 61: Pages 4185–4196