Potatoes are an important food crop and source of income for smallholder farmers across Kenya. Under ideal conditions, farmers can harvest 30–40 tonnes per hectare, then why do the average yields in many potato-growing areas remain around 8–10 tonnes? One of the major reasons is late blight, a destructive disease caused by Phytophthora infestans. In favourable conditions i.e., rainy season, the disease can spread rapidly and destroy an entire field.
Potato late blight is characterised by rapidly spreading brown lesions on the leaves, damaged stems, and reddish‑brown tuber rot. Many farmers depend heavily on synthetic fungicides to protect their crops, but that dependence has led to fungicide resistance. Hence, to control the spread and manage the disease effectively, it is imperative to incorporate proper integrated disease management strategies.
How Resistance Develops?
As populations of P. infestans bring genetic variation, some of them may carry traits that render them less sensitive to a particular fungicide. When the same fungicide is repeatedly applied, susceptible pathogens are killed while those with resistant traits survive. The problem becomes detrimental when farmers repeatedly use fungicides with the same mode of action. Such frequent applications create strong selection pressure, giving resistant pathogens more opportunities to survive and multiply. Kenya’s climate further accelerates the problem. Late blight thrives under cool, wet and humid conditions, which are common in many highland potato-growing regions. Frequent rainfall, heavy dew and high humidity allow the pathogen to reproduce and spread rapidly.
What is Happening in Kenya?
Evidence from potato-growing areas highlights the scale of this challenge as it was reported that in Nyandarua County, almost 65.8% of farmers were found using a single type of fungicide. This clearly indicates the lack of biocontrol solutions in the fields. During wet seasons, spraying frequency of fungicides was recorded as weekly or even more frequently. Meanwhile, very limited awareness of biological control and integrated disease management, shown by only about one-third of farmers, aggravates the concern further. Variety choice is another important factor. Shangi, one of Kenya’s widely grown potato varieties, is moderately susceptible to late blight. There are more tolerant varieties such as Asante and Sherekea, however, their adoption by farmers is still low. Research into improved and hybrid potatoes has also shown promising results, including varieties with multiple resistance traits that can maintain strong yields with little or no fungicide application.
Where Lies the Solution?
Reducing fungicide resistance will require several measures. Using resistant varieties should act as the first line of defence as they can reduce disease pressure and the need for chemical protection. Kenya is also developing potatoes containing multiple resistance genes in locally important varieties. If approved and made accessible to farmers, these could provide another dimension towards alleviating fungicide dependence. In addition, rotating products with different modes of action and using approved combinations can also slow the development of resistance. Certified, disease-free seed helps prevent infected material from introducing the pathogen into new fields. Removing infected debris, destroying crop residues, rotating potatoes with non-host crops can all reduce inoculum and disease spread.
Biological control deserves greater attention as well. Fungal antagonists such as Trichoderma harzianum, chitosan-based formulations along with neem extract have shown potential in supressing the growth of P. infestans in Kenyan research. Lastly, stronger monitoring is ever essential. Tracking pathogen populations can help identify emerging resistance before it becomes widespread. In that case, AI-based forecasting can help farmers anticipate periods of high disease risk and apply suitable chemical control only when they are most needed rather than following routine spraying schedules.
Conclusion
Pesticide resistance is already making late blight management more difficult and costlier for Kenyan potato farmers. Given that it is a challenge involving pathogen biology, farming practices, seed systems, climate, and access to substantial information, addressing it will require maintaining a balance between conventional strategies and biocontrol solutions. The goal is to incorporate biocontrol solutions as well to reduce fungicide footprint and unnecessary costs, and build a more resilient, sustainable, and eco-friendly potato sector.
References
Late Blight Control: Tajiri 720WP | Vanguard 525WG
Battling Pesticide Resistance in Kenyan Potato Production – The Late Blight Challenge – NPCK
Managing Potato Blight in Kenya: Yield Guide | ShambaIQ
Photo Credit: Potato blight: Symptoms & Control | RHS Advice
