While conducting a field survey in Murungai village within Laikipia County, I meet Wanjiku wa Kinyua with a 20-litre-Knapsack sprayer on her back spraying the young maize crops on her farm. The spray includes a strong-smelling herb known as wild marigold or Tagetes minuta L. This plant is an invasive weed in Kenya and a farmers’ enemy number one because of competing heavily with crops for nutrients. However, Tagetes minuta has been Wanjiku’s best friend that she uses as a botanical pesticide to manage fall armyworm (FAW) and other insect pests attacking crops on her 2-acre farm. The use of pesticidal plants such as Tagetes minuta is an organic-based pest management technique and this sparked my interest to tap this indigenous technical knowledge practiced to fight FAW.
Formulation of Tagetes minuta pesticide: At the flowering stage, Wanjiku harvests Tagetes minuta plants by uprooting. She states that the leaves and flowers are the main components of her botanical pesticide. These plant parts are dried and soaked in water in closed 20-litre plastic containers for five days. Thereafter, her concentrated botanical pesticide solution is filtered using a strainer and is ready for use.
Detecting the presence of FAW: Wanjiku has a monitoring routine that helps both in the early detection of FAW infestation and timely management of the pest. “My monitoring programs start as soon as the maize plants germinate and I therefore, encourage all farmers to practice crop scouting around their farms at least once a week”, Wanjiku said. The most used sampling pattern while scouting is a predetermined zigzag because it ensures that all regions of the farm are scouted. Farmers should look out for FAW eggs, larvae, and damage symptoms like window panes and elongated holes on the leaves, and whorl (funnel) damage with frass. The presence of FAW on maize plants signals that pest management action should be taken in order to prevent further crop damage.
Application of Tagetes minuta pesticide: Wanjiku starts application of the formulation only after the young maize plants have seven fully developed leaves. First, she conducts efficacy trials on a few infested plants to assess the insecticidal activity against FAW and also to determine the appropriate concentration that will not cause leaf scorch. Highly concentrated formulations are diluted with equal quantities of soapy water. Because the FAW feeding activity is higher during the night, the sprays are usually done late in the evening or very early in the morning when the larvae are active and not hiding. These sprays are applied directly to the whorls and top leaves of all maize pants on the farm including both infested and healthy plants. Wanjiku said, “A single application of Tagetes minuta serves a dual purpose of killing the FAW larvae and protecting the healthy plants from a possible infestation”. She has also observed that this botanical pesticide has both quick knockdown activity and long-lasting efficacy against FAW. She added, “Also, I use dilute solutions of Tagetes minuta to fight black aphids on beans and whiteflies attacking my potatoes and tomatoes”.
Integrating Tagetes minuta pesticide with other IPM-based practices: Wanjiku is well aware that FAW cannot be effectively managed by a single pest control strategy. She, therefore, employs other practices such as intercropping maize and beans to help reduce pest pressure and the physical control method of handpicking and crushing FAW eggs and larvae. Also, she has prepared a concoction of chili pepper and ash, which she normally applies on the leaf whorl of infested maize plants.
The utilization of such indigenous technical knowledge in pest management will help reduce conventional pesticide usage and associated negative impacts on human and environmental health. Wanjiku explained, “Initially I would go to agrovet stores and buy chemical pesticides based on the dealers’ recommendation, but now I prepare organic pesticides at my home.” She also added, “This indigenous practice has resulted in reduced use of synthetic chemicals and contributed to the production of safe and organic food on my farm. My pesticides are homemade, easy to prepare, and the ingredients are easily available, which helps to cut down my production costs”.
The key takeaway from Wanjiku is that Tagetes minuta has both preventive and curative pest control attributes against a range of insect pests. Therefore, the successful integration of this botanical pesticide into the existing IPM programs will greatly lower FAW infestation and promote organic maize farming. Her parting shot was “I am encouraging farmers to stop using synthetic chemicals to fight crop pests and instead turn to our indigenous pest management practices because they are effective”.
Grace Kinyanjui is a plant pathologist working with Embu University
Email: gracekinyanjui11@gmail.com