Agriculture Reference
In-Depth Information
subsequently. CMD incidence and severity were uniformly high in all five districts
surveyed between 1990 and 1992 and severe losses were reported (Otim-Nape
et al.,
1998). However, the decline in production that occurred in Masindi, Kiboga and
parts of Apac was not as drastic as in Kumi or Soroti. This was associated with the
very wide range of varieties being grown in western districts and, especially in
Masindi, there has been a big increase in the area of Tongolo and other locally-
selected varieties which have some degree of tolerance. The GCF project has also
had an important influence in providing farmers with virus-resistant varieties.
Masindi was included in the original 1991 project and operations were extended to
Lira and parts of Apac in 1992 (Otim-Nape
et al.,
1997). Nase 3 and other improved
varieties soon accounted for a substantial proportion of the cassava grown in these
districts and by 1996 there had been a considerable diffusion of this material into
non-project areas (Bua
et al.,
1997). However, from subsequent surveys it is
apparent that many farmers have since reverted to the use of locally selected
varieties now that the CMD problem has abated and resistance to CMD is no longer
an over-riding requirement. Resistant varieties predominated in only 8% of the
plantings assessed in Masindi in 2003 when the overall incidence and severity of
CMD were generally intermediate (Bua
et al.,
2005).
20.4.6 Districts south of Lake Kyoga
The northern areas of Mukono and Kamuli districts to the south of Lake Kyoga
received little attention until 1994, when surveys were made of the incidence and
severity of CMD in representative areas and assessments were made along main and
feeder roads traversing the areas east and west of Kamuli township. It then became
possible to relate the epidemiological situation in the area to previous findings
elsewhere in Uganda (Otim-Nape
et al.,
2000). Six distinct zones were distinguished,
using an ecological approach, and they were shown to occur in a consistent and
predictable sequence from pre-epidemic areas in the south to post-epidemic areas in
the north:
•
Zone 1: the pre-epidemic zone,
characterized by few whiteflies on cassava, a
low incidence of CMD and little or no evidence of spread by whitefly.
Symptoms generally mild and the overall disease situation benign.
•
Zone 2: a transitional zone,
where CMD incidence and spread were variable,
but somewhat greater than in Zone 1.
•
Zone 3: the epidemic zone,
characterized by generally high population
densities of whiteflies, very rapid spread of CMD and severe symptoms, mainly
on the youngest leaves of affected plants.
•
Zone 4: a zone of chronic and severe infection,
where CMD was so prevalent
that farmers had little option but to plant infected cuttings; growth and yield
were seriously impaired and many plantings were abandoned before harvest.
•
Zone 5: a post-epidemic zone,
in which cassava production had largely been
abandoned, except by the few farmers who had introduced uninfected planting
material from elsewhere.
