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Distribution, incidence and severity of cassava diseases and pests in Mozambique
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Two countrywide surveys were conducted in April-May and May-June 2004 throughout the cassava growing belt of Mozambique including several provinces: Gaza, Inhambane, Sofala, Manica, Zambezia, Nampula and Cabo Delgado. Both surveys were planned to assess the distribution, incidence and damage severity of diseases and pests that affect cassava production in Mozambique. Using the methodology developed by the International Institute of Tropical Agriculture (IITA), 202 and 175 cassava fields between 4-8 months old were sampled for pests and diseases in April-May 2003 and May-June 2004, respectively. The results of both surveys showed in the case of diseases that cassava mosaic disease (CMD) was found to be the most widespread disease in Mozambique although the distribution, incidence, and severity varied among provinces, among fields and within fields. The most severe damage was recorded in Gaza, Sofala and Nampula where the average scores were above 3 on a 1-5 damage scale but only in a limited number of sample fields. In other provinces, the disease was either absent or damage symptoms were slight to moderate (2-3). The DNA analysis of the leaf samples coIlected in 2004 throughout the country revealed the presence of several strains of CMD virus including, the African Cassava Mosaic Virus (ACMV), the Eastern African Cassava Mosaic Virus (EACMV), and a combination of both African and EastAfrican Cassava Mosaic Virus (ACMV+EACMV) in 80.5% and 7.6% of the field samples respectiveIy. The devastating East African Cassava Mosaic Virus - Ugandan Strain (EACMVUG2) was absent from all sampled fields. The presence of cassava brown streak disease (CBSD) was confirmed as a serious threat particularly in two of the three Northern provinces of Zambezia and Nampula and at lesser extent in Cabo Delgado. However, the severity was the highest in Zambezia and in the district of Nakala in Nampula province. The other known common tropical diseases of cassava such as the cassava bacterial blight (CBB) and cassava anthracnose disease (CAD) were of minor importance. The cassava green mite (CGM), Mononychellus tanajoa Bondar remained a problem in the southern provinces (Gaza, Inhambane) where the exotic predatory mites Typhlodromalus aripo De Leon was not yet established.. CGM infestations were followed by whitefly (WF) infestations in a rank-order hierarchy of infestation rates. Although generally known as vectors of the cassava mosaic disease (CMD), the high whitefly population densities recorded in some locations (>lo0 adults per plant, e.g. in Zambezia province), was considered a direct pest causing considerable leaf damage and covering plants with sooty molds. The incidence and damage severity of other common pests of cassava (i.e. cassava mealybug, termites, and grasshoppers) appeared insignificant.