ABSTRACT The field experimental study was conducted to investigate or determine and analyse the interactive effect of better agronomical practices such as cropping system, irrigation, compost‐fertilisation, planting dates and resistant varieties on the cassava mosaic disease (CMD) and cassava brown streak disease (CBSD) disease presence, incidences and severity through morphological detection technique. The qualitative and quantitative primary data were collected and analysed, through Generalised Model Analysis of Variance (ANOVA), linear regression analysis, GENSTAT and JMP Pro software from this research field experiment study which were laid out in a RCBD design with three blocks and four replications in different location sites. The study took place in Mara and Coastal regions, at Nyasirori Butiama district and Nyegina and Busungu‐Majita Musoma rural district and Msoga Bagamoyo Coast region between October 2021 and August 2023. The results findings show that the disease incidence and levels of severity varied or differed significantly among the four location sites and between the two provinces or zones, Coastal and Mara of the Lake zone, at p < 0.001 level of significance. However, the findings show that there were greater levels of disease incidence and severity in Mara region means (1.9199) particularly Nyegina and Busungu‐Majita villages (2.034632) and (2.0002706), respectively, than Msoga Coast region and Nyasirori Mara region, which both recorded low levels of disease incidence and severity of (1.8509) and (1.65536), respectively. But likewise, the higher mean for disease severity scale score showed to decline progressively from (4.2 ± 0.24) Nyegina, (3.2 ± 0.14) Busungu‐Majita, (2.5 ± 0.2) Msoga and (2.0 ± 0.21) Nyasirori having the lowest level of severity. Moreover, the results also found that there was significant influence at p < 0.001 level of significance with agronomic practice treatment, particularly the application of compost FYM + solely or in combination with irrigation supplementation on reducing and controlling the disease incidence and severity, similarly with growth stage and varietal influence. However, conversely again, the result findings had shown significant reduction and management of the disease incidence and severity levels following treatment application of agronomic practices with FYM and Fertilisation (1.817703), Monocropping + FYM + Irrigation (1.8238636) and Irrigation + FYM + Crop rotation (1.7921402) treatments. Similarly, with the varieties influence, particularly with Mkuranga 1, Kipusa, Chereko and Kiroba, had shown the lowest means (1.285871), (1.474808), (1.711939) and (1.819277), respectively, among the varieties tested. However, the best results for disease prevention, management and control, and thus the recommended application rates of compost FYM + Fertiliser materials were found to be lower and/or ranging between 40 and 60 kg per row equivalent to 20.0–32.0 t ha −1 application rates and 30 kg NPK and 10 kg CAN ha −1 depending on soil type (i.e., too poor and too sandy or sandy–sandy loam) and fertility status of the soil, since even lower rates still have shown significant control. Finally, this will have a tangible benefit of reducing the diseases pandemic to farmers and cassava crop stakeholders, agriculture industry sector on the increased crop productivity performance, yield and more importantly the government policy on increased use and application of compost FYM and fertilisers and a very low cost of production countrywide.