Plant Health, Climate Change and Trade - TradeMark Southern Africa

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national SPS systems to implement policies vary among countries and will affect countries'
ability to deal with new SPS risks created by climate change.
3. The impact of climate change on phytosanitary risks
The relationship between climate, plants and plant pests and diseases can be explained by
the "disease triangle" as changes in CO2 concentration in the atmosphere, seasonality,
temperature and rainfall threatens to change world patterns of comparative advantage in
crop production by creating new ecological niches that will affect crop production and alter
the distribution, incidence and intensity of plant pests and diseases.
Temperature can affect critical stages (e.g. survival between seasons or reproduction rate)
in the life cycle of plant pests and pathogens that cause plant disease. Changes in
temperature and humidity may affect the susceptibility of host plants and therefore lower
plant resistance to emerging pests or it may have an effect on the development of fungal
and bacterial diseases. Furthermore, higher CO2 levels may increase the competition
pressure between weeds and crops, the abundance of certain pathogens, such as rusts, or
may increase foliar density and leaf wetness that makes infection by fungal pathogens more
likely.
The emergence of unexpected pests and diseases that occur because of changing climatic
conditions have been observed when new vectors, selection and recombination of disease
genotypes occur, when plant species and varieties mix, and when pests and vectors are
introduced without their natural enemies.
Climatic conditions have been drivers of the evolution of many migratory systems as
migratory pests exploit seasonal changes and weather conditions that may assist or hamper
their dispersal. Migratory pests such as locusts and the African armyworm are unusual
because they undergo density-dependant phase changes from solitary to gregarious and are
dependent on temperature, rain and vegetation. When there is sufficient rain, migrations will
take the insects to patches of green vegetation for feeding and to habitats humid enough for
them to lay eggs. Studies indicate that migration patterns are changing with current changes
in temperature and humidity. Altered wind patterns may also contribute to the changes in the
spread of wind-borne pests and diseases.
Many plant species are adapted to specific habitats that occupy a narrow range along
altitudinal and latitudinal climatic gradients. As temperatures increase an upward migration
of plant communities and their associated pests and disease vectors occur at high-altitude
locations such as the East African highlands. Any increase in the frequency or severity of
extreme weather conditions such as droughts, heat waves, windstorms or floods may also
disrupt the predator-prey relationships that normally keep pest populations in check.
4. The likely impact of new phytosanitary risks on trade
Aflatoxins are mycotoxins that cause developmental and immune system suppression,
cancer, and death and pose serious health risks for humans and animals in Africa. Changes
in temperature and humidity may predispose host crops such as maize and groundnuts to
aflatoxin contamination because of altered crop development and by affecting insects that
COP 17 -­‐ Trademark Climate change impact on phytosanitary risks