Cassava is an important cash crop in tropical lands. In Kenya it is grown for income and food, and covers 77,502 ha with an output of 841,196 tonnes. Most cassava-breeding programmes use symptom expression for selection and detection of viruses. Molecular and/or serological techniques to accurately diagnose viruses are required. Information on the responses of varieties to virus infection helps in assessing the rate of crop degeneration over time. This study evaluated seven cassava breeders’ germplasm, a local susceptible variety (Kibanda meno) and improved (Shibe) to cassava mosaic disease (CMD) under high disease pressure conditions. Populations of the whitefly vector, Bemisia tabaci (Gennadis), and the severity and incidence of CMD, were recorded during the growth period. Infection was determined through symptom severity, disease incidence, enzyme-linked immunosorbent assays (ELIZA) and polymerase chain reaction (PCR) assays. The mean number of whiteflies was higher in the dry season (3 MAP) compared to the wet season (6 MAP) of crop growth. The incidence of CMD was highest in Kibanda meno (>70%) and lowest in Shibe and Tajirika. The mean CMD severities in the tested genotypes was highest in Kibanda meno (>1.5) and lowest in Shibe and Tajirika. PCR assays proved to be a more sensitive disease diagnostic tool compared to ELISA in the detection of cassava mosaic virus. However, both ELISA and PCR detected CMD in asymptomatic cassava samples. The study confirms that the absence of CMD infection cannot be assumed from an absence of visual symptoms on the leaves. This underscores the need for multiple detection tools.