How To Deal With Napier Stunt Disease

By Dr Jolly Kabirizi          

Napier stunt disease (NSD) is caused by a group of phytoplasma, 16SrXI strain bacteria. A leafhopper is the vector of Napier stunt phytoplasma. The disease is currently a major threat to Napier grass fodder production in Uganda.

Symptoms of Napier stunt disease

• Affected plants remain stunted, have short internodes, bunchy appearance and produce very low biomass yields.

Napier stunt disease symptoms

• There is twisting or curling along the mid-rib starting at leaf tips, leaves reduced to short sword like stubs.
• Under severe dry seasons, the plants dry completely.
• The disease is much more severe and prevalent in poorly managed Napier grass fields and during dry seasons.
• Napier stunt disease incidence of 10% to 90% has been recorded in parts of Uganda where farmers practice zero grazing dairy production system.
• Disease incidence is highest in the Lake Victoria Crescent areas because of high number of stall-fed animals that depend on purchased fodder due to limited land and lowest (less than 10%) in highland areas such as Mbale and Kabale districts.
• The disease is spread through movement of infected planting materials and fodder.

 Implications of Napier stunt disease on dairy cattle production

• Napier stunt disease causes considerable losses and affect both human and animal welfare in various ways stemming from social and economic aspects.
• The catastrophic disease is mostly characterized by the drastic decline in herbage biomass that can go up to 100% in severely affected fields.
• Decline in milk yield of over 50% due to inadequate feeds.
• Increased cost of production as farmers have to depend on purchased feed.
• High labour demands in areas where farmers walk long distance in search of feed from communal areas, and food and nutritional insecurity as home consumption of milk decreases.

Management of the stunting disease

• Inspect the field regularly, remove and burn all diseased Napier grass stools.
• Use tolerant varieties as a component of an integrated management approach could be an environmentally friendly way to contain this disease in smallholder dairy industry.
• A number of new napier grass accessions (Kakamega 1, Kakamega 2, NARO (National Agricultural Research Organization Napier) NAP1; NARO NAP 2, NARO NAP 3, Pakchong variety and others), tolerant to Napier stunt disease and have high biomass dry matter yield (10 to 100 tons per acre per year) are being promoted in different agro-ecological zones of Uganda.
• Improve the health of the Napier grass by applying manure or fertilizer.
• When harvesting, cut Napier grass plants leaving a stubble height of 5cm above ground level.
• If the area is seriously affected use alternative grass species such as Brachiaria grass.
• Sensitise neighbours about transmission mechanism and management of the disease.