FALL ARMY WORM: Strategies for effective management



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BY Professor Rohan Rajapakse


Emeritus Professor of Entomology University of Ruhuna and


Former Executive Director Sri Lanka Council of Agriculture Research Policy


Fall Army worm Spodoptera frugiperda (Lepidoptera; Noctuidae) is a quarantine pest and has been identified as a most destructive insect pest of Maize/Corn. This insect has originated in Americas and invaded the African region in 2016 and was detected in India the following year and perhaps would have naturally migrated to Sri Lanka last year from India. Now it is reported that FAW is present in all districts of Sri Lanka except Nuwara Eliya and Jaffna. During winter in the US, the pest is found in Texas and Florida and subsequent summer when it gets warmed up the pest migrates up to Canadian border. The corn belt of China is also at a risk due to its migratory habit and the cost to Africa due to this invasion exceeds $ 6 billion. Maize is a staple food crop in Africa and millions depends on it for food. Hence in Africa and now in Asia it is a global food security issue for millions of people that could be at a risk if FAW is not controlled. The adult moth migrates very fast almost 100 km every night and nearly 500 km before laying 1500 eggs on average. The entire life cycle lasts 30 days in tropical climate. There are 6 larval instars and mostly the destruction is caused by the last 3 instars and the growing moth pupates in the soil for 10-12 days and the nocturnal adults lay eggs on leaves for about 10 days The pest thrives on about 80 host plants but the most preferable host is Corn/Maize In sri Lanka the preferred hosts includes Kurakkan and Sugarcane in addition to Maize. The symptoms of damage- scrapping of leaves, pin holes, small to medium elongated holes. Loss of top portion of leaves fecal pellets in leaf whorl which are easily recognizable. The Comb is also attacked in later stages with a heavy infestation, after removing the FAW affected portion of the comb the remaining portion is still suitable for consumption and there is no fear of any toxicity. There are two morphologically identical strains- Maize strain that feeds on maize and sorghum and rice strain that feeds on rice and pasture grasses. However in Sri Lanka only the maize strain has been detected so far. FAW thrives in a climate where drought is followed by heavy rains on a similar way we have experienced last year.


Although new agricultural insect pests are found in Sri Lanka from time to time a number of factors make FAW unique (FAO Publication 2018)


1 FAW consumes many different crops 2 FAW spreads quickly across large geographical areas 3.FAW can persists throughout the year. Therefore Sri Lanka needs to develop a coordinated evidence based effort to scout FAW for farming communities and effective monitoring by the research staff


Management


Since the pest has already arrived in Sri Lanka the Government/ Ministry of Agriculture should formulate short term, mid term and long term strategies for its effective management with all stakeholders. Also it has to be clear that a single strategy ex pesticides will not help in effective control but a proper combination of tactics such as integrated pest management should be employed in long term. In short term the recommended pesticides by the Department of Agriculture should be employed along with cultural and sanitary control strategies. These strategies have now been formulated and what is required to enlighten the farmers and people by utilizing the trained staff. The country should be place on war footing and an emergency should be declared in the affected areas to coordinate the control strategies. The integrated control tactics such as cultural control should be integrated with pesticides based on the recommendation of the research staff. The residues should be destroyed after harvest and avoid late planting and staggered planting. The Ministry of Agriculture should create awareness among the farmers and train the farmers on early detection of egg masses found on leaves and destroy them by hand. The pesticides for FAW control is recommended by the Department of Agriculture (Please contact Registrar of Pesticides of the Department of Agriculture for the recommended list of Pesticides) and they have to make it available at subsidized rates or given free with technical information considering the emergency. When the larvae are small early detection and proper timing of pesticides are critical for elimination of the pest. With this outbreak some farmers and the private sector is engaged using highly hazardous pesticides which should be avoided to make way for sustainable alternatives. The Department Entomologists should train the farmers for early detection of egg masses when present on 5% of the plants and when 25% of the plants show damage symptoms and live larvae are present on war footing. The economic threshold has been calculated as 2-3 live larvae per plant and the control strategies should commence as soon as this threshold is detected by visual observation. The development officer’s majority Agriculture and science graduates working in Divisional Secretariats are already trained on pest control and their participation on training the farmers for early detection and pesticide selection and application warrants the strategy. Some of the recommended pesticides are as follows: Chlorantraniliprole 200g/1SC: Trade name Corogen, Emamectin benzoate 5%SG: Trade name Proclaim,, Flubendiamide 24% WG : Trade name Belt. The Principle Entomologist of the Dry Zone Research Station of the Department of Agriculture ( Mrs KNC Gunawardena) has prepared an effective on line presentation on FAW control and this has to be shared by all. The African country Ghana has declared a state of emergency in response to this invasion as Maize is a staple crop which should be followed by us in Sri Lanka.


The long term strategies include early detection of the pest, stopping its spread and initiation of research programmes to identify tolerant varieties and granting permission to import such varieties as seeds. The country should work out a biological control strategy by breeding and releasing FAW parasitoids regularly. In the US, larval parasitoids such as Apanteles marginiventris, Chelonus insularis and Microplitis manilae have contributed to keeping the pest population down along with egg parasitoids Trichrogramma spp and a similar programme should be initiated in the affected districts. Finally, the best option is to establish a task force with the involvement of entomologists, extension personnel along with the administrators and scientists working in the universities to ensure the country is safe with regard to food security.


(The author has read for a PhD at University of Florida Gainesville in USA in 1985 and his PhD thesis exclusively deals on Fall army worm parasitoids and its ecology)


 
 
 
 
 
 
 
 
 
 
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