Legume based Profitable Intercropping System for Management of Fall Armyworm in Maize

Maize (Zea mays L.) is the most important cereal crop cultivated in an area of 180.63 million hectares in 165 countries across the world recording a production of 1134 million tonnes growing at an average annual rate of 3.46 per cent (Anonymous, 2020a). It is widely valued for its extensive use as feed, fodder and as raw material for various industrial applications. In India, maize ranks third among cereals after rice and wheat, both in terms of area and production, registering maximum growth rate among food crops (Rakshit and Chikappa, 2018). Maize is attacked by nearly 130 species of insect pests in India among which borers cause upto 20-30 per cent yield losses (Atwal and Dhaliwal, 2002). In recent times, Fall armyworm [FAW; Spodoptera frugiperda (J.E. Smith)] is emerging as the most destructive pest of maize in India since its report in May 2018. Its rapid spread to more than 90 per cent of maize growing areas of diverse agro-ecologies of India within a short span presents a major challenge to small holder maize farmers, maize-based industry, as well as food and nutritional security (Suby et al., 2020). The value of crop loss is estimated at between US$2,481 million and US$6,187 million (Shylesha et al., 2018). In 2018, this notorious, pestiferous and havoc able pest has entered India.  In India, 33-36 per cent loss in yields have been attributed to this pest as per the preliminary reports (Jagdish et al., 2019; Aruna et al., 2019). During 2019, Fall armyworm was reported in nearly 3 lakh hectares in various states of India (Karnataka, Madhya Pradesh, Rajasthan, Maharashtra, Mizoram, Tamil Nadu, Telangana and Andhra Pradesh) and was estimated to affect over 7-8 lakh hectares in 2020-21 (Anonymous, 2019; Aizawl, 2019).
       
Chemical control is regarded as an emergency control measure for the outbreak of unprecedented invasive pest, FAW in the region. ICAR-Indian Institute of Maize Research has recommended group of pesticides like emamectin benzoate, spinosad and chlorantraniliprole against FAW Anonymous (2020b). However, FAW is known to develop resistance against synthetic pesticides if chemical control is exclusively employed for its management (Burtet et al., 2017). It is not pragmatic to control FAW population by depending only on a single management practice but rather on an integrated pest control strategy (Chimweta et al., 2020 and Kumela et al., 2019) It is therefore crucial to identify environmentally friendly and cost-effective strategy for the management of this pest. Under these situations intercropping can play a significant role to enhance the productivity and profitability per unit area and time through more coherent use of land, water and solar energy, besides assuring indemnity against crop failure. Intercropping cereal with legume is recognized as the most popular agricultural practice in many developing countries of the world (Songa et al., 2007 and Kiwia et al., 2019). Maize, sorghum and pearl millet are the most familiar cereal species, whereas bean, soybean, cowpea, pigeonpea, groundnut are legume species. The cereal species is grown for primary importance and the legume species that helps in fixation of atmospheric nitrogen into the soil is added for secondary importance of increased crop production and reduced pest and weed incidence (Khan et al., 2014). Intercropping of legumes with main crop to reduce the pest pressure is one of the promising integrated pest management strategies and study of such a technique will be useful for formulating an effective and remunerative integrated pest management module to combat fall army worm in Maize.

The experiments were executed in a 0.14 ha area at Regional Agricultural Research Station (Acharya NG ranga Agricultural University), Anakapalle andhra Pradesh during kharif (August to October) of 2019, 2020 and 2021 to explore the consequences of intercropping on incidence of fall armyworm in maize and the cost economics invloved.
 
Cultivation of maize with intercrops
 
The experiment was performed in a randomized block design, having three replications for each treatment. Maize crop was sown at a spacing of 60 cm × 15 cm, sesame seeds in the experimental field. The standard recommended crop practices were followed and the crops were raised as purely rainfed. Manual weeding was taken up twice and no plant protection measures were taken up during the entire crop growth period. Six intercropping systems were evaluated in comparison to sole maize crop. The intercrops were raised with main crop in replacement series. Maize (Zea mays L.; Variety: CP-333) was grown as the main crop along with red gram (Cajanus cajan L.; Variety: LRG-52), black gram (Vigna mungo L.; Variety: PU-31), green gram (Vigna radiata L.; Variety: WGG 42), cowpea (Vigna unguiuculata L.; Variety: local), groundnut (Arachis hypogaea L; Variety K-9) and soybean (Glycine max L.; Variety JS-335) were grown as intercrops.
 
Damage of fall armyworm and beneficial insects
 
Data had been recorded using standard sampling methods from ten plants selected randomly per plot. The data pertaining to per cent plant damage and per cent leaf damage by fall armyworm were recorded and the naturally occurring predators were also recorded as number of spiders/coccinellids per plant. Data was recorded in various intercropping systems and sole maize from initial appearance till crop maturity at fifteen days interval and the seasonal means were computed. All the coccinellids were reported together as one entity, regardless of the family to which they belonged. Similarly, all species of spiders were reported together.
 
Evaluation of yield and cost economics
 
Plot wise and replication wise yield was recorded separately for sesame (main crop) and intercrops and the total per hectare yield was calculated according to the following formula (Bondre et al., 2017).
     
System equivalent yields
 
The yields of the various intercrops are transformed into the equivalent yield of main crop on the basis of the price of the crop produce. The system equivalent yield (SEY) is calculated as follows (Chetty and Reddy, 1987).
   
Where,
Y_i = Yield of i^thcomponent.
e_i = Equivalent factor of i^thcomponent or price of i^thcrop.
 
Benefit cost ratio
 
Benefit cost ratio (B: C ratio) was calculated with respect to different intercropping systems versus sole sesame for managing sucking pests, according to following formula (Bondre et al., 2017).
   
Statistical analysis
 
The experiments have been replicated thrice during three subsequent years. The data from field experiments was screened by ANOVA (analysis of variance) after getting transformed into Öx+0.5 using AGRES as per Gomez (1984). Pooled RBD ANOVA was done using Microsoft excel. Critical difference was calculated at 5% probability level and treatments mean values were compared using Duncan’s multiple range test (DMRT) as per Gomez and Gomez, 1984.

Field experiments to study the effect of intercropping on fall armyworm incidence and beneficiary insects (coccinellids and spiders) in maize were conducted in three subsequent kharif (August to October) seasons for three consecutive years (2019, 2020 and 2021) and the pooled data was statistically analyzed. The results and discussion are presented hereunder.
 
Effect of intercropping on incidence of fall armyworm in maize
 
Pooled mean data acquired from the field experiments of three consecutive years on effect of intercropping on incidence of fall armyworm in maize are presented in Table 1. Among six intercropping systems studied, maize+cowpea recorded significantly lowest mean per cent infested plants (45.0 per cent) at 75 days after sowing which equated statistically with maize+green gram (45.5 per cent). The next effective intercropping system was maize+black gram (55.7 per cent) followed by maize+red gram (58.2 per cent) followed by maize+groundnut (58.8 per cent) followed by maize+soybean (59.6 per cent), all of which were statistically on par with each other. Maize as a sole crop registered the highest mean per cent infested plants (76.3 per cent) at 75 days after sowing.
 

       
The present investigation indicated the significantly least per cent of mean damaged leaves due to fall armyworm at 75 days after sowing was manifested in maize+cowpea (33.8 per cent) and maize+green gram (34.6 per cent). The next effective intercropping systems were maize+black gram (46.8 per cent) followed by maize+groundnut (49.1 per cent) followed by maize+red gram (50.5 per cent) followed by maize+soybean (51.0 per cent), all of which were statistically on par with each other. Sole maize at 75 days after sowing exhibited the highest mean per cent damaged leaves (58.3 per cent).
       
The current study concurs with the stated findings of Degri et al., (2014); Girma et al., (2018) and Clovis et al., (2020), where intercropped maize with leguminous crops resulted in a significantly lower FAW infestation, compared with mono-cropped maize as certain crops and their arrangements will help disrupt host location by pests and act as repellents or deterrents reducing oviposition due to presence of allelochemicals.
 
Effect of intercropping on predators population in maize
 
As depicted in Table 1, the mean population of predatory coccinellids was significantly more in maize+cowpea (1.19 per plant) along with maize+green gram (1.11 per plant). The next better performing intercropping system with regard to coocinellid population was maize+black gram (0.90 per plant). All the other intercropping systems viz., maize+red gram (0.21 per plant), maize+groundnut (0.13 per plant), maize+soybean (0.10 per plant) were  statistically on par with sole maize (0.12 per plant). Statistically higher number of spiders (1.01-1.03 per plant) was recorded in maize+cowpea (1.14 per plant) and maize+green gram (1.13 per plant), the spider population per plant was 1.01 in maize+black gram. The spider population was low in maize+red gram (0.13 per plant), maize+soybean(0.12) and maize+groundnut(0.11 per plant) which were on par with spiders recorded in sole sesame(0.14 per plant).
       
Comparable findings have been reported by Seran and Brintha (2010); Girma et al., (2018) and Uday kumar et al., (2021). Habitat manipulation as a method of conservation biological control which employs intercrops in the main crop field to conserve the beneficial insect fauna like natural enemies. Crop diversification with various temporal and spatial arrangements reduces pest incidence while increasing the population of beneficial arthropods.
 
Impact of intercropping in maize on economics of yield
 
The data on impact of intercropping in maize with legumes on yield economics are depicted in Table 2. The system equivalent yield (SEY) of the intercropping systems under study ascertained that the maize+cowpea achieved highest SEY of 5230 kg per ha followed by maize+green gram (5160 kg per ha) followed by maize+black gram (4900 kg per ha) and then by maize+red gram(4760 kg per ha)followed by maize+groundnut (4700 kg pe ha) and maize+soybean (4600 kg per ha. The yield realized by sole maize was 4560 kgha^-1. Highest returns were generated from maize+cowpea (Rs.115060.00 per ha) followed by maize+green gram (Rs.113520.00 per ha) followed by maize+black gram (Rs.107800.00 per ha) followed by maize+red gram (Rs.104720.00 per ha) followed by maize+groundnut (Rs.103400.00 per ha) followed by maize+soybean (Rs.101200.00 per ha) and lastly sole maize (Rs.100320.00 per ha). The calculated costs of cultivation of various intercropping systems are shown in Table 2. Upon comparing the benefit cost ratio (BC ratio), the maize+cowpea proved to be the most profitable with BC ratio of 4.11 followed by maize+ green gram (4.05) followed by maize+black gram (3.85) followed by maize+red gram(3.49) as presented in Table 2. The BC ratio of maize+groundnut (2.95), maize+ soybean (2.89) and sole maize (2.87) were nearly the same. There are umpteen findings elucidating the higher income generated due to intercropping when compared to sole crop. Monetary benefits owing to intercropping in maize has been recorded by Nirmal et al., (2020), Assefa and Dereje (2019) and Maitra et al., (2019). Kiwia et al., (2019) and Khan et al., (2014) have also expressed the positive consequences of cereal legume intercropping by registering low pest, disease and weed incidence and also being more remunerative. 
 

Intercropping in maize with legumes especially pulses like cowpea and green gram followed by black gram and red gram significantly reduced the fall armyworm incidence and has also shown positive influence in enhancement of natural enemies like coccinellids and spiders in the crop eco system. These systems were also proven to be sufficiently profitable in respect of higher yields and higher Benefit Cost Ratio.

The author is highly thankful for the resources provided by Acharya NG Ranga Agricultural University, Andhra Pradesh to conduct the present study.