EFFICACY OF SEED DRESSERS AND RESISTANCE OF SORGHUM VARIETIES IN THE MANAGEMENT OF FALL ARMYWORM

Sorghum plays a crucial role in ensuring food security for millions of people in East Africa. However, the production of sorghum is significantly hindered by the damaging effects of fall armyworm (FAW), leading to food insecurity in the region. This study aimed to assess the effectiveness of seed dressers and the resistance of different sorghum varieties in managing FAW under real field conditions. The study evaluated four seed dressers (Thiamethoxam, Imidacloprid, Lindane, and Carbofuran) and screened five sorghum varieties (Wagita, Seredo, Gadam hamam, KARI Mtama 1, and IESV24029SH) for their resistance to FAW. A local check variety called Nakhadabo was included for comparison purposes. The experiments were conducted at Kiboko and Alupe KALRO/ICRISAT Research Stations using a randomized complete block design with a factorial arrangement and three replications for two seasons (2018 and 2019). The collected data included observations on dead heart symptoms, FAW leaf feeding damage, number of larvae per plant, days to 50% flowering, panicle damage symptoms, plant height, and grain weight. 

Lindane (4) showed the lowest occurrence of dead heart symptoms compared to untreated controls (6.2). All seed dressers demonstrated lower levels of leaf feeding damage compared to the untreated controls, with Lindane (9) being the most effective in reducing such damage. The seed dressers showed variation in the number of days to 50% flowering, with Imidacloprid (147 days) exhibiting early flowering at Alupe, and Thiamethoxam (125 days) showing early flowering at Kiboko. Lindane (3.3 larvae) and Thiamethoxam (3.9 larvae) resulted in a lower number of FAW larvae per plant compared to the other seed dressers and untreated controls. Lindane (5.5) was the most effective seed dresser in reducing panicle damage symptoms caused by FAW compared to other seed dressers and the untreated controls (7.4). Lindane (295cm), Carbofuran (296cm), and Thiamethoxam (296cm) led to shorter plant heights compared to other seed dressers and untreated controls. Carbofuran (2.34g) resulted in the highest grain weight per plot compared to other seed dressers and untreated controls.

Significant differences (P≤0.05) were observed among the sorghum varieties, and KARI Mtama 1 (5) displayed the lowest dead heart symptoms compared to other varieties. Alupe recorded higher FAW leaf feeding damage compared to Kiboko. Nakhadabo (4.2), KARI Mtama 1 (5.3), and Wagita (5.9) exhibited resistance by displaying lower leaf feeding damage, while IESV24029SH (10), Gadam hamam (8.2), and Seredo (8.1) showed susceptibility with higher leaf feeding damage. Alupe recorded a higher number of FAW larvae per plant compared to Kiboko. Nakhadabo (1.3 larvae), KARI Mtama1 (2 larvae), and Wagita (2.3 larvae) had a lower number of larvae per plant, while the other varieties showed susceptibility. Sorghum at Kiboko flowered earlier than at Alupe, and Gadam hamam (52.3 days) flowered earliest at Kiboko, while Nakhadabo (67 days) flowered earliest at Alupe. Higher panicle damage symptoms were observed at Alupe compared to Kiboko. KARI Mtama 1 (1), Wagita (1.3), and Nakhadabo (2.3) exhibited moderate resistance to panicle damage symptoms compared to other varieties. Plant height was higher at Kiboko but lower at Alupe. Gadam hamam (103cm) and IESV24029SH (105cm) showed shorter plant heights compared to other varieties. Grain weight was higher at Kiboko compared to Alupe, and Wagita (3.6g) displayed the highest grain weight compared to the other varieties.

This study identified Thiamethoxam, Imidacloprid, Lindane, and Carbofuran as effective treatments against FAW during the vegetative stages and development of sorghum. These seed dressers could be incorporated prior to planting to protect sorghum seeds from early FAW infestations. Additionally, Nakhadabo, KARI Mtama 1, and Wagita varieties were found to exhibit resistance to FAW feeding damage on sorghum, making them suitable for managing FAW infestations during the growth periods, particularly in high or anticipated infestation areas

 

 

 

 

 

Grain sorghum Sorghum bicolor L. Moench, (Family: Poaceae), takes the fifth position globally after maize, rice, wheat and barley as a vital cereal grain in terms of area under cultivation and production (FAOSAT, 2017). The world sorghum production is 64.7 million tons (USDA, 2016). USA is the world leading producer of sorghum with 9.2m metric tons. In Africa, Nigeria is the largest producer of sorghum with 6.9m metric tons. In Eastern Africa, Ethiopia leads in sorghum production with 4.8m metric tons (Table 1) (FAOSAT, 2017). Sorghum follows maize as the most important cereal in Africa with 22% of the total cereal area (Feeding Africa, 2015). Sorghum accounts for 76% of grain consumption in South Sudan (FEWS NET, 2018), while the total production in 2017 was 667,000 tons (FAOSAT, 2017). Sorghum ranks first in South Sudan (Richard. Z et al., 2015) and comes fourth after maize, wheat and rice in Kenya as reported by Central Bureau of Statistics (CBS, 2016). Sorghum is adapted to the environments prone to droughts that receive 300-760 mm of annual rainfall. It does well in areas between 500m to 1700m above sea level (ASL) (Muui, 2014). In E. Africa, sorghum is a food security crop, mainly for smallholder farmers (Timu et al., 2012; Muui et al., 2013).

As reported by Kilambya and Witwer (2013) and Gichangi et al. (2015), sorghum crop gives hope that Sub-Saharan Africa can still attain maximum levels of production even in areas occasioned by climate change. Because of being drought tolerant, sorghum is referred to as the plant kingdom’s camel (Fetene et al., 2011). The characteristics that make sorghum a drought- resistant crop are the deep root system and its ability to cease growth during the dry spells (Whiteman and Wilson, 1965; FAO, 2015). The crop has smaller leaf area, heavy and waxy cuticles that cover the leaf surface, making them well adapted to high temperatures and efficient in reducing the rate of transpiration during drought conditions (Munyua, 2010). Sorghum requires one-half to two-thirds the amount of rainfall compared to maize (Hancock, 2000). Sorghum is a vital diet for over five hundred million people in more than thirty countries in Arid and Semi-Arid (ASA) parts of Africa (ICRISAT, 2015), Asia and Central America. Sorghum has many uses as food, feed, fibre and fuel (ICRISAT, 2015; FAO, 2015). In South Sudan, sorghum is a key cereal crop widely grown in the country, that serves many purposes such as ‘Kuin’ (ugali) with meat or vegetables’ broth, kisera (leavened pancake), and local brewed wine (mou) and sorghum grain stew (nyiny). These also include the most famous dishes called ‘Akop or Wal-wal’ a food prepared from sorghum flour (unfermented dough) and ‘Diong’ (ugali with cow’s butter or ghee).

Sweet sorghum cultivars with high sugar content are the only types of sorghums that provide stems which can be chewed like sugarcane, production of sugar and syrup (Laopaiboon et al., 2007; CGIAR, 2015). Sorghum is a wellspring of nutritional elements for millions of the poor small-scale farmers (Makokha et al., 2002). The nutritional values of grain sorghum have been found to have the healing properties that prevent the lifestyle diseases and chronic disorders. Sorghum food is free of gluten and is recommended for patients who are intolerant to gluten and those having abdominal pains. Sorghum food has a low glycemic index that reduces the risks of diabetes. Sorghum is also rich in antioxidants, polyphenols, dietary fibre and magnesium and contains a low content of fat (Ciacci et al., 2007; Dayakar et al., 2014). Dried stalks of sorghum serve different purposes that include; bedding, roofing, fencing and paper production (CGIAR, 2015). Norwegian Refugee Council (NRC, 2004) reported that, in the developing countries, sorghum products are not only used as food or as fuel for cooking, but also as leather dye and as physical supports for the climbing crops like cucumbers and yams.

Sorghum is one of the most important food crops, especially for the poor and hunger-stricken families in eastern Africa (Timu et al., 2012). Despite the ability of sorghum to grow successfully in drier regions of Sub-Saharan Africa, its production is constrained by about 150 insect pests, and of these, more than hundred (100) pests have been reported in Africa alone (Kruger et al., 2008). The damage by insect pests results in an annual yield loss of over $ 1billion in drier areas of the globe (ICRISAT, 1992). Among the major insect pests in E. Africa that devastate sorghum production, is the recent introduced fall army worm (Spodoptera frugiperda). FAW is reported to be an important economic pest of sorghum in Brazil and El Salvador (Molina et al., 2001; FAO, 2017). Andrew (1988) reported that, FAW feeding damage in sorghum causes yield loss that ranges from 55 to 80% in the Americas. In E. Africa, no seed dressers and resistant sorghum varieties that have been used for the control of FAW infestation. Therefore, this study was undertaken to investigate the efficacy of seed dressers and resistance of sorghum varieties in the management of fall armyworm in Eastern Africa.

As part of an IPM being widely used today against FAW, seed treatment with insecticides such as Thiamethoxam (Apron star) and Imidacloprid (Gaucho) is a crucial part of an effective fall armyworm control measure that could be used for the management of FAW in E. Africa. According to Cosette (2014), seed dressers have good efficacy on many below ground soil pests and the insect pests that attack sorghum at seedling stage yet they are still not widely screened for use against FAW in sorghum, especially in E. Africa. ICRISAT (2017) reported that, seed dressing can protect the seedlings from pests and fungi up to 40 days, improves crop density by a quarter and yields by up to 50%. Protecting the seeds and young plants from the very start gives them a chance to develop vigour and to survive during the critical first days after planting, even under high insect pressure (Syngenta, 2017). Not much has been done to evaluate the efficacy of seed dressers and the resistance of sorghum varieties in managing the FAW in Eastern Africa. On the other hand, no sorghum varieties have been identified and evaluated for resistance to fall armyworm infestation in the region. In E. Africa, much attention is being directed to the damage the pest causes to maize and not much is known about its impact on sorghum. Therefore, this study focused on evaluating the efficacy of seed dressers and the resistance of selected sorghum varieties to the infestation of FAW for control and management of this pest. Smallholder farmers are the most negatively impacted by the fall armyworm infestation and therefore, the results of this research will help them in a bit to control this pest in sorghum.

The main objective of this study was to evaluate the efficacy of seed dressers and the resistance of sorghum varieties to FAW and in managing early FAW infestation to improve sorghum production.

The specific objectives of this study were: 

1- Sorghum seed dressing is effective against fall armyworm in selected sorghum varieties. 2- Selected sorghum varieties have existing resistance to fall armyworm infestation.