Evaluation of the efficacy of intercrops for the management of Maruca vitrata (Kharif 2016-17)
At first week after flowering, no. of M.vitrata webs/50 rachis ranged from 5.0 (Pigeonpea + pearlmillet) to 9.0 (Pigeonpea sole crop) (Table 1). At second week after flowering, natural infestation of spotted pod borer has increased and 23 M.vitrata webs/50 rachis was recorded in pigeonpea sole crop. During this period, among the intercropped pigeonpea crops, comparatively less number of webs was observed in pigeonpea+pearlmillet intercropping system (18/50 rachis) and pigeonpea+sorghum intercropping system was on par with this with 20 M.vitrata webs/50 rachis. This is in accordance with the general opinion that arthropod pests out breaks were more likely to occur in monocultures than in polycultures. Similarly, Nath and Singh (1998) stated that, intercropping with non-host plants reduced the incidence of insect pests whereas intercropping with similar plant type increased the pest problems.
Observations recorded at third week after flowering revealed significantly less number of webs (16/50 rachis) in pigeonpea+pearlmillet intercropping system as against 25/50 rachis in pigeonpea sole crop. Pigeonpea + sorghum and Pigeonpea + maize intercropping systems were on par with each other with 20 to 21 webs/50 rachis. The same trend was observed at fourth and fifth weeks after flowering also. The mean no. of
M.vitrata webs/50 rachis was less in pigeonpea intercropped with pearlmillet (10.4) followed by pigeonpea intercropped with maize (13.4) and pigeonpea intercropped with sorghum (13.0) while in pigeonpea sole crop, it was 16.2.
Shravankumar et al., (2018) reported low relative abundance of pigeonpea insect pests when pigeonpea was intercropped with sorghum followed by pearl millet when compared to the sole crop of pigeonpea. Per cent pod damage by spotted pod borer was also significantly reduced in pigeonpea + sorghum than in other treatments.
Mohammed and Rao (1998) reported 15.0 to 9.7 per cent reduction in
H. armigera pod damage in pigeonpea + sorghum intercropped plots than the sole crop.
At early pod development stage, comparatively less pod damage (8%) was observed in pigeonpea+pearlmillet intercropping system, while in pigeonpea sole crop it was 13 per cent. Pigeonpea + sorghum and Pigeonpea + maize intercropping systems were on par with each other with 10 to 11 per cent pod damage. This is in agreement with the reports of
Sule Hassan (2018) who reported less population of aphids (
Aphis craccivora Koch.) and thrips (
Megalarothrips sjostedi Trybom) and less incidence of cowpea pod borer,
Maruca vitrata in cowpea + sorghum intercropping system.
Ampong-Nyarko et al., 1994 also confirmed the importance of intercropping as a method of reducing pest attack in cowpea. In contrast,
Nampala et al., (2002) reported increased pod borer and pod sucking bug populations in cowpea when mixed cropped with sorghum. At pod development stage, minimum pod damage of 11% was recorded in pigeonpea+pearlmillet intercropping system followed by pigeonpea + maize (13%) and pigeonpea + sorghum (15%). In pigeonpea sole crop, 18 per cent pods were damaged by this borer. At pod maturity stage in pigeonpea+pearlmillet intercropping system, 13 per cent pod damage was observed and this was significantly less than the pod damage (20%) observed in pigeonpea sole crop. In pigeonpea + sorghum and pigeonpea + maize intercropping systems, 17% and 16% pod damage was recorded respectively and both were on par with each other. Same trend was observed with the observations at pod harvest stage.
Sekhar et al., (1997) and
Rao et al., (2003) reported that sorghum intercroping with pigeonpea reduced pigeonpea sucking insect pest, leaf hopper infestation significantly than the sole crop. When the mean per cent pod damage values from early pod development stage to harvest were observed, reduction in
M. vitrata pod damage (10.8%) was very clear due to the intercropping of pearlmillet while mean pod damage in sole crop was 17.3 per cent. The present findings were in agreement with the statement of
Ahoaka-atta et al., 1993 that damage by pod borers on cowpea was less when intercropped with maize. However,
Ezueh (1991) reported increased infestation by spotted pod borer in cowpea when intercroped with cereals.
Singh (2002) observed maximum pod borers damage in sole pigeonpea crop than the intercropped pigeonpea. He reported that the intercrops in pigeonpea
i.e., sorghum, rice, pearlmillet and maize were on par with each other in reducing the pod borer damage however, significantly superior to sole crop. He has also recorded minimum per cent damage of tur pod fly,
Melanagromyza obtuse in pigeonpea + sorghum intercropping system.
Coccinellid beetle population was more in intercropped pigeonpea (14-15/10 plants) than the sole crop (12.0). Spider population ranged from 5 to 6 in intercropping systems and in sole crop 2 spiders per 10 plants were observed. In intercropping systems, less spotted pod borer damage and more natural enemy population were observed during this study. Synchronized flowering times of short duration pigeonpea and sorghum would have facilitated the transfer of natural enemies from intercrops to pigeonpea and this may be the one of the reasons for the lower insect population.
Evaluation of the efficacy of intercrops for the management of Maruca vitrata (Kharif 2017-18)
At first week after flowering among the different treatments, no. of
M.vitrata webs/50 rachis ranged from 3.0 (pigeonpea + pearlmillet) to 6.0 (pigeonpea sole crop). No significant difference in spotted pod borer incidence was observed among pigeonpea+maize, pigeonpea+sorghum and pigeonpea sole crop systems. At second week after flowering, pigeonpea+pearlmillet intercropping system recorded less number (3.0) of
M.vitrata webs/50 rachis and pigeonpea + maize intercropping system was on par with this with 4.0 webs/50 rachis (Table 2). In pigeonpea sole crop, 7 webs were recorded per 50 rachis. At third week after flowering, significant difference was observed in the infestation of spotted pod borer between pigeonpea +pearlmillet intercropping system (4/50 rachis) and pigeonpea sole crop 8/50 rachis. Same trend was noticed during fourth week after flowering also. At fifth week after flowering, pigeonpea+pearlmillet and pigeonpea + maize intercropping systems were found to be on par with each other with 3.0
M.vitrata webs/50 rachis while in pigeonpea sole crop, it was 8.0.
At the end of the trial, pigeonpea intercropped with pearlmillet was found to be effective in reducing the infestation of spotted pod borer by recording a mean number of 3.0 webs per 50 rachis followed by pigeonpea intercropped with maize (4.4). In pigeonpea sole crop, mean number of webs per 50 rachis was 7.0. Reduced incidence of cowpea aphid when intercropped with maize than on sole cropped cowpea was reported by
Sinthananthem et al., (1990) and Ogenga Latigo et al., (1992). At early pod development stage in pigeonpea sole crop, 10 per cent pod damage was observed. When compared to this, pigeonpea+pearlmillet and pigeonpea + maize intercropping systems recorded 5 per cent pod damage and were found to be effective in reducing the damage by this borer. At pod development stage, pearlmillet intercropped pigeonpea recorded less pod damage of 7 per cent as against 14 per cent in pigeonpea sole crop. Pigeonpea + sorghum and pigeonpea + maize intercropping systems were on par with each other with 9 to 10 per cent pod damage.
Intercropping showed positive influence in reducing the insect infestation. This suggests that pest migration after initial establishment was possibly inhibited by the non host plants as physical barriers to inter or intra row migration within intercrop treatment. The conspicuous pest reduction in sorghum – pigeonpea dicrop combination may be because sorghum made inter row migration very difficult for spotted pod borer,
Maruca vitrata during later stages of pigeonpea crop development. The reduction of
H.armigera infestation due to sorghum as intercrop can be attributed to two factors. The simultaneous flowering of pigeonpea and sorghum might have caused distribution of
H. armigera population on main crop pigeonpea and intercrop, leading to less incidence of the pest on main crop. Overlapping of pod formation and flowering of pigeonpea with ear-head formation of sorghum might have reduced the feeding damage to main crop pigeonpea by the pest (
Srinivasa Rao et al., 2006).
Same trend was observed with the observations at pod maturity and pod harvest stages. With regard to mean per cent pod damages in various treatments, intercropping pigeonpea with pearlmillet was effective in managing the infestation of spotted pod borer and recorded a mean per cent of 6.8 while in sole pigeonpea crop it was 12.8 per cent. Intercropping sorghum in cowpea reduced the damage of legume pod borer on cowpea
(Omalo et al., 1993). Flower, seed and pod damage levels were low in pigeonpea intercropped with maize, sorghum, ragi, pearl millet and cowpea (
Ganapathy, 1996). Intercropping with sorghum, sowing during the first fortnight of June and removing leguminous weeds reduced pod borer damage in pigeon pea cultivar,
(Gopali et al.,2010). In intercropping systems, low insect infestations are reported due to many factors that include physical protection from wind, shading (
Litsinger and Moody, 1976), prevention of dispersal (
Kayumbo, 1975) production of adverse stimuli, olfactory stimuli camouflaged by main crop (
Aiyer, 1949), presence of natural enemies (
Tonhasca, 1993) and availability of food (
Fukai and Trenbath, 1993). Lowered resource concentration, other diversionary mechanisms, trap cropping, plant density factors and plant physical obstruction account for 22.5 per cent reduction in insect population. Increase in natural control agents
i.e., predators and parasites account for 15 and 10 per cent respectively. Masking, camouflage and repellency account for 12.5 per cent each. Overall natural enemy action controlled about 30 per cent of crop pests and the remaining known cases were controlled by other factors (
Baliddawa, 1985).
Due to the presence of intercrop in between the main crop, crop microclimate variables
i.e., canopy temperature (Tc), canopy - air temperature differential (CATD) and relative humidity in crop canopy (CRH) were altered. Tc was higher in pigeonpea with intercrops than in sole crop of pigeonpea. Sorghum as intercrop increased the Tc to 32.5°C compared to 30.5°C in sole pigeonpea (30.5°C). High CRH values were recorded in pigeonpea with sorghum (
Srinivasa Rao et al., 2006). The higher relative humidity under tall canopy together with shading is likely to favour the activity of insects in intercrops also (
Srinivasa Rao et al., 2004).
Natural enemy population (coccinellid beetles and spiders) were more in intercropped pigeonpea than the sole pigeonpea crop. Flowering crops can be used as attractant plants to encourage coccinellids such as
C. sexmaculata,
C. septempunctata and
Brumoides suturalis in and around pulses (
NIPHM, 2014). Studies by
Ogenga-Latigo et al., 1992 and
Kyamanywa et al., 1993 have shown that in crop mixtures, variations were observed in herbivore load which inturn increased the abundance of natural enemies.
Duffield and Reddy, 1997 stated that the generalist predators belonging to major taxa including anthocorids, coccinellids, chrysopids, spiders etc. are more common on sorghum.
Evaluation of the efficacy and economics of IPM modules for the management of M.vitrata (Kharif 2018-19)
At first and second weeks after flowering, in IPM module I (pigeonpea and pearlmillet intercropping, NSKE (5%) spray at bud initiation stage and need based spraying of indoxacarb 15.8 EC - 0.7 ml/lt), less number of
Maruca webs were recorded
i.e., 23 and 21 respectively as against pigeonpea sole crop (35 and 38 respectively) (Table 3). IPM module I was followed by IPM module II (pigeonpea and sorghum intercropping, NSKE (5%) spray at bud initiation stage and need based spraying of indoxacarb 15.8 EC - 0.7 ml/lt) and IPM module III (pigeonpea and maize intercropping, NSKE (5%) spray at bud initiation stage and need based spraying of indoxacarb 15.8 EC - 0.7 ml/lt) and both were on par with each other. The study of Nath and Singh (2006) also confirmed the efficacy of pigeonpea + sorghum intercropping system when integrated with the spray of NSKE (5%) in reducing the damage by pigeonpea gram pod borer,
Helicoverpa armigera.
At 7 days after second spray, considerable reduction in number of webs in IPM modules was observed. As against 45 webs/50 rachis in pigeonpea sole crop, IPM module I was found to be effective by recording 19 webs/50 rachis. This was followed by IPM module II (24/50 rachis) and IPM module III (26/50 rachis). The same trend was noticed at 14 days after second spray and 7 days after third spray except IPM module II and IPM module III were on par with each other.
At 14 days after third spray, minimum pod damage of 6 per cent was recorded in IPM module I while in pigeonpea sole crop pod damage was 18 per cent. At pod maturity stage and at harvest, IPM module I was proved to be effective by recording minimum number of webs/50 rachis. When compared to sole pigeonpea crop, IPM modules II and III were proved to be effective in minimizing the spotted pod borer damage. However, among the three modules, IPM module I in which pearlmillet was intercropped with pigeonpea was found to be best. Spraying of eco-friendly biopesticides
i.e.,
B. thuringiensis, NSKE 5% and nimbecidine at flowering or pod formation stage and 20 days later were found to be effective in reducing the pigeonpea pod damage, grain damage and grain weight loss due to
H.armigera (
Nath and Singh, 2006).
With regard to the natural enemy population, coccinellid beetles were more in IPM module I, IPM module III and untreated control and all were on par with each other (9-10/10 plants) (Table 4). IPM module II recorded comparatively less number of coccinellids (8/10 plants) but was on par with the IPM modules I and III. This mixed result may be due to the spraying of chemical insecticides in the IPM modules. No significant correlation was observed with the abundance of spider population in various treatments. In IPM module I, yield of 770 kg/ha was obtained as against 550 kh/ha in sole pigeonpea crop. Among the IPM modules, high B:C ratio of 1:1.66 (Table 4) was recorded with IPM module I.
Many authors reported the efficacy of the IPM packages including various insect management components in pigeonpea ecosystem.
Yelshetty et al., (2003) reported the highest benefit-cost ratio of 2.30 in biointensive module (
HaNPV - 250LE/ha, hand collection,
B. thuringiensis - 1 kg/ha, NSKE 5% followed by
HaNPV - 250LE/ha) over the recommended package of practice (1.76) during heavy pest load in pigeonpea ecosystem. Bird perches (50/ha), mechanical collection, spray of neem based insecticides at 50% flowering and
HaNPV at early pod set and need based spraying of insecticides at flowering and podding stage against pod borer complex on early sown pigeonpea (3rd week of June) recorded less damage by pod borer (14.6 - 26.6%), pod wasp (1.8- 3.0%) and pod fly (2.4- 4.0%) with a grain yield of 362-530 kg/ha and benefit cost ratio of 1.73 to 1.91
(Gajendran et al., 2006). Samiayyan and Gajendran (2009) reported that the IPM package comprising of bird perches (50 nos./ha), collection and destruction of pod borer larvae, pheromone traps (12 nos./ha), spray of
Ha NPV (1.5 x 1012 POB/ha), spraying of indoxacarb 14.5 SC (0.75 ml/l) at 50 per cent flowering or monocrotophos 36 WSC (2 ml/l) at the time of flowering/early pod formation stage recorded minimum cumulative pod borer damage (16.27 to 31.51%) compared to farmers’ practice (30.56 to 47.50 %) with higher grain yield (655 to 1397 kg/ha) and C:B ratio (1:1.7 to 1:2.5).
