Maize lethal necrosis (MLN) is a devastating plant disease than can cause malformed cobs and premature death of crops, among other symptoms. The disease was first reported in Kenya between 2011 and 2012. A recent study looked at the importance of developing management strategies among farmers to combat MLN.
MLN is considered one of the major biotic constraints that affects maize production in Kenya. “Maize yield losses to MLN have been reported to range from 30% – 100% depending on the variety, stage of disease infection and prevailing environmental conditions,” says a recently published study on the disease’s impact on Kenyan maize stores, titled: “Maize production systems, farmers’ perception and current status of maize lethal necrosis in selected counties in Kenya“.
Maize is an important cereal crop in Sub-Saharan Africa and is considered a staple crop by approximately 70 million people. In 2019 alone, fields to grow the crop covered a total of 40 million hectares in Sub-Saharan Africa, according to the United Nations’ Food and Agriculture Organization (FAO).
Understanding the disease
“To develop MLN management practices that are effective, efficient and easily adaptable to the small-scale farmer, there is a need to understand farmers’ knowledge in relation to the different aspects of the disease. Understanding the role of knowledge in farmers’ practices is also an important starting point for developing a management strategy that fits the context of the smallholder farmer maize production practices.
“In Kenya, studies have been done to understand the viruses associated with MLN and their geographical distribution. However, no studies have been conducted to get insight into farmers’ knowledge and their role in MLN control. Hence, the present study focuses on understanding farmers’ know-how on scientific knowledge and recommended management practices on MLN and also on their local knowledge of the disease management. “
The study also crosses through five Kenyan counties that are known for their maize production, and these include Bomet, Nakuru, Kirinyaga, Embu, and Narok.
“Of the 406 farmers who were interviewed in the present study, there was almost equal representation by both males (56.4%) and females (43.6%),” the study reflected. “Statistically, there was a significant association between the gender of the farmer and the county where they were from, with Embu (23.6%) and Kirinyaga (36.7%) counties reporting a high number of females. Therefore, efforts to promote MLN disease management strategies should be structured in such a way that they are easily accessible to both males and females.”
About 95% of those surveyed had completed some type of formal education, whether it was in elementary school (grades 1–8), secondary school (grades 9–12), or college. The percentage of uneducated farmers was under 5%. Bomet county has the largest percentage of graduates from universities with 17.9%, whereas Narok had none.
Approximately 1.48 t/ha of maize was projected to be produced during the 2020 – 2021 growing season, with 77.3% of farmers reporting average yields of less than 2 t/ha. Nakuru county respondents reported an average yield of 4.41 t/ha and MLN incidence rates in their farms that were less than 10%. These farms were those that were situated in the Molo region at a height of 2411.02 meters above sea level. Due to weather that makes it difficult for insects to survive, previous research have found that MLN incidence is low in higher altitude places.
Pest and weed control
” Use of herbicides for weed control in combination with manual weeding was also common among farmers in Kirinyaga (41%). Use of biological and cultural methods for pest control was common in Nakuru (26%). Farmers in Nakuru, at an altitude of 2411.02 m above sea level, reported having minimal pest damage saying when it rains, the pests are washed off.
“Other biological control methods reported included the use of ash, soil, tobacco, and Ariel, a popular washing detergent. In addition, some farmers reported to being against the use of pesticides especially when growing maize for their own use while others cited lack of money to buy the pesticides. However, some farmers were of the opinion that there has been a change in the pests affecting the maize crop, as the cultural control methods were very effective (eliminating the pests by 90–100%, according to farmers’ observation) five to ten years ago, but they were noting these methods becoming less effective.”
Improved maize varieties were cultivated in the majority of counties, according to 87% of the respondents. The hybrid DUMA 43, chosen for its drought resistance and quick maturation qualities, was the most often planted in Kirinyaga. It was followed by Pioneer 3253, chosen for its favourable market quality traits since it is sold as green maize.
In Kirinyaga, several hybrids were also planted, including DK777, Pannar, Sungura, baby corn, DK8031, and DK9089. The hybrid cultivars DK777 and H614 are most prevalent in Embu county, whereas H6213 and Narok and Nakuru counties have the most H6213 plantings. These hybrids were chosen because of how well they fit into the various agro-ecological zones.
There is a need to introduce and diversify the maize varieties grown in each region as just a few of the hybrids are now cultivated in each county, the study observed.
Farmers were shown images of MLN-infected maize plants during the survey. MLN was known by several names in the various counties, yet the bulk of the farmers (80%) could still recognise it. In the current study, the severity of MLN is highlighted by the fact that 93% of the farmers reported seeing MLN on their farms. According to statistics, there was no relationship between the farmer’s age or gender and their understanding of MLN. However, there was a statistically significant discrepancy between the county’s and the farmers’ means.
“Across all the study areas, more than 70% of the respondents reported that MLN is higher during the short rains (sunny season) and off-season plantings,” the study observed.
“Environment plays a critical role in disease development and the dry and hot conditions during off season and short rains/sunny season would be a favourable environment for reproduction and movement of vectors to transmit MLN causing viruses. A few of the farmers (6%) reported MLN being high any season that maize is planted. This could be attributed to maybe late plantings in long rains which have been reported to contribute to high MLN incidence or delayed rains (which simulate sunny season in the long rains).”
Most notable symptoms
“Yellowing was reported by 60% of the farmers as the most common symptom associated with MLN. Few farmers could identify the early onset MLN symptoms (chlorotic mottle on leaves), making it difficult for the farmer to control the disease early before it spreads. Premature plant death and male sterility were not identified by farmers as MLN symptoms. Therefore, yellowing was the prominent MLN symptoms recognized by the farmers who had limited know-how of other symptoms associated with MLN.
“About 46.3% of the farmers reported observing MLN when the maize was at the pre-flowering stage and 36.5% at the vegetative stage. Other prominent stages were the post-flowering stage (7.3%), the 4 – 5 leaf stage (5.3%), and the flowering stage (2.2%). About 2% of the farmers noted that MLN can affect the maize plant at any growth stage. The results of this study are concurrent with previous studies reporting that MLN can affect maize plants at all growth stages.”