Abstract:
Growers’ surveys took place in all sixteen potato growing regions of South Africa in 2013
and 2014. The agro-ecological climate of these regions is diverse and potato is produced in
rainy or dry seasons, in winter or summer seasons, or year round. Growers were asked how
often in ten years crops suffered more than 25% yield losses due to extreme weather events
related to precipitation events such as hail, floods and droughts, and to temperature-related
events such as frost and heat waves. Simultaneously they were asked their opinion about
occurrence and severity of diseases caused by potato viruses, fungi and bacteria and pests
such as nematodes, tuber moths, aphids and leaf miners. Weather related hazards resulted
in losses over 25% virtually each year in the Gauteng growing region due to hail, frosts and
floods; losses occurred less than once every five years, for example due to extremely high
temperatures, in the Sandveld area where growers take a risk by producing potatoes in hot
summers. Regarding the biotic factors, every pest or pathogen assessed was reported to
occur on at least one farm in each growing region. Countrywide the lowest frequency of 50%
was recorded for powdery scab whereas the insects tuber moths, leaf miners and aphids
were reported most frequently, by between 88% and 98% of the growers. The complex of
silver scurf and black dot resulted in the greatest yield losses in all growing regions, followed
closely by tuber moth, early blight and the blackleg / soft rot disease complex. Yield losses
due to potato virus Y, potato leaf roll virus and aphids were not reported as being very
severe. When the growers’ perceptions of severity of biotic factors were accumulated,
significant differences between the regions appeared, with the Eastern Cape most prone with an accumulated score of 700 due to an array of pests and diseases, and the North-
West with a score of only 50 mainly attributed to root knot nematodes. Growers were also
asked how frequently biocides were applied to potato to control soil-borne organisms
(nematicide and seed treatment), foliar fungi or insects. There were no significant
correlations between frequency of biocide applications and severity of the disease as
reflected in yield losses, most likely because growers use biocide applications as insurance
against pests and diseases. This is common among crop farmers around the world.
Although potato production in South Africa appears to carry more risks than production
elsewhere, South African commercial potato growers are economically competitive when
compared to growers in other areas of the globe, with comparable planting conditions and
risks.
