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Yield loss at the different growth stages in soybean due to insect pests in

Ghana

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Yield loss at the different growth stagesin soybean due to insect pests in GhanaMumuni Abudulai a , Abdulai B. Salifu b , Danial Opare-Atakora a ,Mohammed Haruna a , Nicholas N. Denwar a & Inusah I.Y. Baba aa Northern Region Farming Systems Research Group/ScientificSupport Group, CSIR-Savanna Agricultural Research Institute,Tamale, Ghanab Administration, CSIR Head Office, Accra, Ghana

Version of record first published: 24 Jul 2012

To cite this article: Mumuni Abudulai, Abdulai B. Salifu, Danial Opare-Atakora, Mohammed Haruna,Nicholas N. Denwar & Inusah I.Y. Baba (2012): Yield loss at the different growth stages in soybeandue to insect pests in Ghana, Archives Of Phytopathology And Plant Protection, 45:15, 1796-1809

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Yield loss at the different growth stages in soybean due to insect pests in

Ghana

Mumuni Abudulaia*, Abdulai B. Salifub, Danial Opare-Atakoraa,Mohammed Harunaa, Nicholas N. Denwara and Inusah I.Y. Babaa

aNorthern Region Farming Systems Research Group/Scientific Support Group, CSIR-SavannaAgricultural Research Institute, Tamale, Ghana; bAdministration, CSIR Head Office, Accra,Ghana

(Received 21 June 2012; final version received 21 June 2012)

Insecticide protection at the vegetative, reproductive or both vegetative andreproductive (complete) crop growth stages and untreated control was used toassess yield loss due to insect pests at the different growth stages of soybean inGhana from 2007–2009. The objectives were to determine the economicimportance of the two major insect pest guilds in soybean, viz. defoliators andpod feeders, and when to apply control measures for maximum benefit. Thedefoliators recorded were Podagrica spp., Ootheca mutabilis (Shalberg),Zonocerus variegatus L., Sylepta derogata F., Spodoptera littoralis Boisduval,Amsacta spp. and Helicoverpa armigera Hubner. The pod feeders recorded werethe pod-sucking bugs (PSBs) Riptortus dentipes F., Thyanta sp. Aspavia armigeraF., Nezara viridula L. and Dysdercus volkeri Schmidt. Generally, insect densities,pod and seed damage were lower while seed yields were significantly greater andsimilar in plots that were protected at the reproductive stage against PSBs andthose protected at both vegetative and reproductive stages. Yield loss rangedbetween 25.8 and 42.8% in untreated plots, 11.1 and 34.3% in plots that wereprotected at the vegetative stage, and 5.2 and 11.3% in plots that were protectedat the reproductive stage. There was a consistent negative correlation betweenyield and numbers of PSBs as well as pod and seed damage. These results showedthat PSBs that attack soybean at the reproductive stage were the most importantinsect pests limiting soybean yield in Ghana.

Keywords: soybean; growth stages; defoliators; pod-feeding insects; yield loss

Introduction

Soybean (Glycine max (L.) Merrill) is an important grain legume crop in the worldbecause of its high protein and oil content (Singh et al. 1987; Proulx and Naeve2009). It is exploited both as subsistence and a commercial crop and is used inhuman and animal nutrition. In Ghana, the seed is processed and consumed invarious traditional dishes, including ‘‘tubani’’, ‘‘kooshe’’ and soya milk, and is alsoused in soups and stews. Soybean is also a good rotational crop for fixing nitrogen toenhance soil fertility (Keyser and Li 1992) which is a major benefit in Africanfarming where fertilisers are beyond the reach of majority of farmers (Bagayoko

*Corresponding author. Email: Mabudulai@yahoo.com

Archives of Phytopathology and Plant Protection

Vol. 45, No. 15, September 2012, 1796–1809

ISSN 0323-5408 print/ISSN 1477-2906 online

� 2012 Taylor & Francis

http://dx.doi.org/10.1080/03235408.2012.706744

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et al. 2000). Moreover, sale of soybean seeds is a major source of income to farmersand foreign exchange in Ghana (Langyintuo 1996).

Despite soybean’s importance, its production is constrained by insect pestswherever it is cultivated. Worldwide, defoliators and pod feeders are the mostdamaging insect pests of soybean (Kogan 1981; Jackai et al. 1990; Sastawa et al.2004; Wada et al. 2006; Musser et al. 2011). In Africa, however, where the crop wasrelatively new, insect pests until recently were not a problem. An increased area ofcultivation over the years due to increased popularity of the crop with farmers hasalso resulted in increased insect pests attack (Jackai et al. 1988; Sastawa et al. 2004).The insects associated with the crop in Africa have been reported by Ezueh and Dina(1979) in Nigeria and Kamau (1980) in Kenya. However, in Ghana except for a fewreports, insect pest profiles on soybeans have not been adequately investigated. Asurvey conducted at Nyankpala in northern Ghana revealed that Spodoptera spp.(Lepidoptera: Noctuidae), Zonocerus variegatus L. (Orthoptera: Pyrgomorphidae),Sylepta derogata F. (Lepidoptera: Pyralidae) and a complex of pod-sucking bugs(PSBs), including Nezara viridula L. (Hemiptera: Pentatomidae) and Riptortusdentipes F. (Hemiptera: Alydidae) are the major insect pests of soybean (Salifu 1993;Abudulai 2004). Several of these insects are indigenous pest species and are alreadypests on other cultivated food legumes, e.g. cowpea. Insecticide protection is theprincipal recourse for the control of these pests in those legumes (Jackai and Singh1987; Salifu 1993).

The farmers in Ghana have complained of the problems of insect pests onsoybean, but there is no quantitative data elucidating the losses attributed to insectsin soybean. The yield loss data are needed to justify the use of inputs in their controland for the development of a comprehensive pest management strategy for the crop.Therefore, the aims of the present study were: (1) to document insect pest profilesand dynamics on soybean; (2) to assess yield loss due to these pests at the differentgrowth stages of the crop. Ultimately, the outcome of the research would be used toevolve a strategy for the control of insect pests in soybean in Ghana.

Materials and methods

Field experiments were conducted at the Research farm of the CSIR-SavannaAgricultural Research Institute at Nyankpala (98420N latitude, 08920W longitudeand 184 m altitude) in Ghana during the 2007, 2008 and 2009 growing seasons. Thesoil type at the field was sandy loam. The soybean cultivar ‘‘Jenguma’’ which issusceptible to insect pests was used and planted on 13 June, 14 July and 10 July in2007, 2008 and 2009, respectively. The experiments were arranged in a randomisedcomplete block design with four treatment replications. The treatments comprised ofinsecticide (1) untreated control, (2) complete protection, from when plants have twonodes on the main stem having trifoliate leaves to beginning of pod maturity or whenpods have lost their green colour (V2–R7), (3) selective control of vegetative pests(mainly defoliators) from 2-node stage to 7-node stage (V2–V7), and (4) selectivecontrol of reproductive pests or pod feeders (mainly PSBs) from bloom to beginningof pod maturity (R1–R7) (soybean development stages described by Fehr andCaviness 1977). The insecticide protection was accomplished with foliar applicationsof cypermethrin 10 EC at 0.02 kg ai/ha. The insecticide was applied at 7–10 daysintervals from the initial application at any crop growth stage. Spray applicationswere made using a CO2-pressurised backpack sprayer with Teejet cone nozzles

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(Spraying systems Co., Wheaton, IL, USA). Plots were 6 rows and 5 m long, spaced at0.75 m between rows and 0.05 m between plants in a row. Blocks were separated by2 m alleys. Pendimethalin as Stomp 4.5 EC was applied at 1.0 kg ai/ha as a pre-emergent herbicide 1–2 days after planting in each year. Plots were weeded as needed.

Sampling of insects

The data were collected weekly on predominant insect pests at the vegetative andreproductive growth stages from V2 to R7. Insect samples were taken from the outertwo rows of each plot using a 1-m square beat cloth (Kogan and Herzog 1980). Twosites were sampled in each plot by placing the cloth between rows, bending plantsfrom one row over and beating them downward to dislodge insects onto the cloth.The numbers of the different insect species on the beat cloth were appropriatelyrecorded. Insect densities in untreated plots were used to assess insect profiles anddynamics on the crop.

Estimation of insect damage and soybean yield

Defoliation was estimated weekly in each plot by randomly picking two leaflets fromeach of 10 plants to assess the per cent leaf surface missing using a scale of 5–100%. Atmaturity, the middle four rows of each plot were harvested and PSB damage to podsand seeds, and seed yield were recorded. A sample of 100 pods from each plot was usedto estimate pod damage, which was the number of shrivelled or flattened pods andexpressed as percentage pod damage. Similarly, the number of seeds with visible stinkbug-feeding scars or those that were shrivelled or decayed were sorted as damagedseeds and expressed as percentage seed damage. The percentage yield loss for each plotwas calculated using the following formula by Walker (1983):

Yield loss ¼ ½ðYield C�Yield UÞ=Yield C� � 100

where Yield C is yield in kg per ha from the plot with complete insecticideprotection; Yield U represents yield from untreated or any other treatment of thesame replicate.

Data analysis

All data were analysed using analysis of variance (ANOVA) and when F-values weresignificant, means were separated at p5 0.05 using the Fisher’s Protected LeastSignificance Difference test (SAS Institute 2003). Insect counts and percentagedamage data where necessary were subjected to log (Xþ 1) and square root orarcsine transformation, respectively, to correct for the lack of normality beforeanalysis (Gomez and Gomez 1983). Pearson correlation coefficients (r) werecomputed between yield and insect pest densities and percentage damage parameters.

Results

Insect pest profiles and dynamics on soybean

Insect defoliators recorded in the field were Amsacta spp. (Lepidoptera: Arctiidae),Z. variegatus, Helicoverpa armigera Hubner (Lepidoptera: Noctuidae), Ootheca

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mutabilis (Shalberg) (Coleoptera: Chrysomelidae), Podagrica spp. (Coleoptera:Chrysomelidae), Spodoptera littoralis Boisduval (Lepidoptera: Noctuidae) andS. derogata. Pod-feeding insects mainly PSBs recorded were N. viridula, Aspaviaarmigera F. (Hemiptera: Pentatomidae), R. dentipes, Thyanta sp. (Hemiptera:Pentatomidae) and Dysdercus volkeri Schmidt (Hemiptera: Pyrrhocoridae). Also, theflower thrips Megalurothrips sjostedti Trybom (Thysanoptera: Thripidae) wererecovered from the flowers.

In 2007, Podagrica spp. and Z. variegatus were recorded throughout the season,which were also the most abundant defoliators (Figure 1(a)). Sylepta derogata wasrecorded from the mid-vegetative stage and populations increased dramatically fromthe late vegetative stage until crop maturity. Populations of H. armigera, S. littoralis,O. mutabilis and Amsacta spp. were low throughout the season. Pod-sucking bugswere recorded from bloom, with D. volkeri and R. dentipes recorded first followed byN. viridula, Thyanta sp. and A. armigera (Figure 1(b)). Thyanta sp. was the mostdominant PSB followed by N. viridula, A. armigera and R. dentipes. Dysdercusvolkeri was the least dominant PSB recorded.

In 2008, S. derogata was recorded from the mid-vegetative stage and was themost dominant defoliator followed by O. mutabilis and Z. variegatus that wererecorded from the beginning of sampling (Figure 2(a)). Densities of Amsacta spp.,Podagrica spp.,H. armigera and S. littoralis were low throughout the season. Amongthe pod-feeding insects, D. volkeri was recorded from the late vegetative to earlybloom stage while N. viridula and A. armigera were recorded from the beginning ofpodding (Figure 2(b)). Nezara viridula was the most dominant PSB recorded,followed by D. volkeri and A. armigera. Riptortus dentipes was the least dominantPSB.

In 2009, defoliator densities except those for S. derogata and Podagrica spp. weregenerally low throughout the season (Figure 3(a)). Populations of S. derogata werethe highest in the season. Nezara viridula was recorded during the late vegetative toearly bloom stage, followed by Thyanta sp. during bloom and R. dentipes duringpodding (Figure 3(b)). Again, N. viridula was the most dominant while R. dentipesthe least dominant PSBs recorded.

Effect of insecticide treatment on insect pest densities, damage and yield

In 2007, the insecticide treatment significantly lowered defoliator densities comparedwith untreated plots (Table 1). The reduction in defoliator densities was greatest inthe plots that received complete insecticide protection. Similarly, the percentagedefoliation was lower in treated than untreated plots, with the lowest defoliationrecorded in the plots that received complete insecticide protection. Like defoliators,significantly fewer PSBs were recorded in treated than untreated plots. Among thetreated plots, the lowest PSB densities were recorded in the plots that receivedcomplete protection. Insecticide protection at the reproductive stage also signifi-cantly lowered PSB densities compared with protection at the vegetative stage. Asimilar effect was observed for percentage pod damage. However, the lowest poddamage was recorded when plants were given complete insecticide protection orprotected at the reproductive stage. There was, however, no significant difference inpod damage between plots that received protection at the reproductive stage andthose that were protected at the vegetative stage. Seed damage was significantlylower in plots that received complete insecticide protection or were protected at the

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reproductive stage compared with protection at the vegetative stage and untreatedcontrol. However, a treatment at the vegetative stage significantly lowered seeddamage compared with untreated control. As expected, seed yield was the greatestwhen plants received complete insecticide protection or were protected at thereproductive stage. There was, however, no significant yield difference between plotsthat received insecticide protection at the reproductive stage and those that wereprotected at the vegetative stage, all of which had significantly higher yields than

Figure 1. Mean abundance and dynamics of (a) defoliators and (b) pod-feeding insects(pod-sucking bugs) in soybean at Nyankpala during the 2007 growing season. Notes: Insectsamples were taken in untreated plots at two sites in each plot using a 1-m square beat cloth.Sampling began at the V2 stage (when plants have two nodes on the main stem havingtrifoliate leaves).

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untreated control. Yield loss caused by insects was significantly higher in untreatedplots than the other treatments.

In 2008, defoliators were significantly fewer in plots that received completeinsecticide protection or were protected at the vegetative stage than untreatedcontrol or those exposed to insects until the reproductive stage (Table 2). Alsopercentage defoliation was lower in plots that received complete insecticideprotection or were protected at the vegetative stage than the other treatments.Significantly fewer PSBs were recorded in insecticide treatments, with the lowestnumbers recorded when plants were given complete insecticide protection orprotected at the reproductive stage (Table 2). As expected, pod damage was lowest in

Figure 2. Mean abundance and dynamics of (a) defoliators and (b) pod-feeding insects (pod-sucking bugs) in soybean at Nyankpala during the 2008 growing season. Notes: Insect sampleswere taken in untreated plots at two sites in each plot using a 1-m square beat cloth. Samplingbegan at the V2 stage (when plants have two nodes on the main stem having trifoliate leaves).

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plots that received complete insecticide protection or were protected at thereproductive stage. A treatment at the vegetative stage also significantly loweredpod damage than untreated control. Also, a lower seed damage was recorded forplots that received complete insecticide protection or were protected at thereproductive stage compared with those protected at the vegetative stage anduntreated control. These resulted in significantly higher seed yields in the completeinsecticide protection plots and those protected at the reproductive stage than those

Figure 3. Mean abundance and dynamics of (a) defoliators and (b) pod-feeding insects (pod-sucking bugs) in soybean at Nyankpala during the 2009 growing season. Notes: Insect sampleswere taken in untreated plots at two sites in each plot using a 1-m square beat cloth. Samplingbegan at the V2 stage (when plants have two nodes on the main stem having trifoliate leaves).

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Table

1.

Effectofinsecticideapplicationtimingoninsect

pests’densities,damageandyield

ofsoybeanatNyankpala,2007.

Insecticide

application

timing

No.of

defoliators

m7

1Defoliation

(%)

No.of

pod

bugsm

71

Pod

damage

(%)

Seed

damage

(%)

Grain

yield

(kgha71)

Yield

loss

(%)

Control

7.7+

0.4

a19.5+

0.3

a3.5+

0.3

a31.5+

1.7

a26.5+

2.5

a1428.3+

54.2

c25.8+

2.4

aVegetativeStage

3.0+

0.2

c6.7+

0.8

b2.0+

0.1

b12.0+

1.3

b14.8+

7.4

b1713.3+

83.0

b11.1+

3.7

bReproductiveStage

4.1+

0.4

b5.5+

0.4

b1.3+

0.1

c8.8+

1.4

bc

10.3+

5.1

c1825.0+

74.1

ab

5.2+

3.2

bComplete

Protection

2.4+

0.1

d3.0+

0.2

c0.5+

0.0

d6.3+

0.9

c6.5+

3.2

c1925.0+

27.4

a–

F62.85

152.61

68.79

71.50

52.18

20.87

16.36

p50.0001

50.0001

50.0001

50.0001

50.0001

0.0002

0.0037

Values

are

means(þ

SE)offourreplicates.Within

columns,means(+

SE)followed

bythesameletter

donotdiffer

significantly(A

NOVA,p4

0.05,Fisher’sProtected

LSD

meanseparation).–,blank.

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Table

2.

Effectofinsecticideapplicationtimingoninsect

pests’densities,damageandyield

ofsoybeanatNyankpala,2008.

Insecticideapplication

timing

No.of

defoliators

m7

1Defoliation

(%)

No.of

pod

bugsm

71

Pod

damage

(%)

Seed

damage

(%)

Grain

yield

(kgha7

1)

Yield

loss

(%)

Control

0.2+

0.0

a21.0+

0.9

a0.5+

0.0

a25.0+

1.3

a30.8+

4.1

a1654.7+

20.0

c26.3+

2.8

aVegetativestage

0.1+

0.0

b9.7+

0.5

c0.3+

0.1

b16.8+

1.8

b20.5+

8.0

a1682.0+

32.4

c23.5+

2.1

aReproductivestage

0.2+

0.0

a15.6+

0.8

b0.1+

0.0

c8.8+

0.9

c4.3+

0.6

b1798.5+

20.4

b10.0+

4.5

bComplete

protection

0.1+

0.0

b7.4+

0.4

c0.1+

0.0

c5.3+

0.9

c3.3+

0.9

b1890.3+

23.3

a–

F7.04

61.48

14.14

52.62

13.26

18.26

7.10

p0.0098

50.0001

0.0009

50.0001

0.0012

0.0004

0.0262

Values

are

means(þ

SE)offourreplicates.Within

columns,means(+

SE)followed

bythesameletter

donotdiffer

significantly(A

NOVA,p4

0.05,Fisher’sProtected

LSD

meanseparation).–,blank.

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protected at the vegetative stage and untreated control. There was no significantyield difference between plots that were treated at the vegetative stage and untreatedcontrol. Also, percentage yield loss was significantly greater in untreated plots andthose treated at the vegetative stage compared with plots that were treated at thereproductive stage.

In 2009, significantly fewer numbers of defoliators were recorded in the plots thatreceived complete insecticide protection than the other treatments (Table 3). Asimilar trend was observed for percentage defoliation. However, significantly fewernumbers of PSBs were recorded when plots were given complete insecticideprotection or protected at the reproductive stage compared to the other treatments.Similarly, percentage seed damage was significantly lower in the plots that receivedcomplete insecticide protection or were protected at the reproductive stage than theother treatments. Moreover, seed yield was significantly higher in the plots thatreceived complete insecticide protection or were protected at the reproductive stagethan the other treatments. Consequently, percentage yield loss was significantlyhigher and similar in untreated plots and those treated at the vegetative stage thanplots that were treated at the reproductive stage.

Relationships between yield and insect densities, defoliation, and pod andseed damage

In 2007, insect defoliator and PSB densities were significantly and negativelycorrelated with yield (Table 4). Also, percentage defoliation, percentage pod damageand percentage seed damage all had significant negative correlation with yield. In2008, PSB densities, percentage pod damage and percentage seed damage weresignificantly and negatively correlated with yield. However, defoliator densitiesand percentage defoliation were not significantly correlated with yield. In 2009,defoliator densities and PSB densities were both significantly and negativelycorrelated with yield. Percentage seed damage also was significantly andnegatively correlated with yield, but there was no significant correlation betweenpercentage defoliation and yield.

Discussion

The defoliators and PSBs recorded in this study were reported by other workers asmajor insect pests of soybean in Africa (Jackai et al. 1990; Anyim 2002, 2003;Sastawa et al. 2004). The defoliators were present from the early vegetative stage,whereas PSBs were recorded from the late vegetative to early flowering stage throughharvest. The dynamics of these insects coincided with the period of suitability of thehost for their feeding (Wada et al. 2006). The populations were generally low early inthe season and increased as the season progressed, which was consistent with thereports by other workers (Jackai and Singh 1987; McPherson 1996; Baur et al. 2000;Bundy and McPherson 2000; Anyim 2003; Smith et al. 2009). This population build-up over the season was probably due to more suitable temperatures and relativehumidity that favour insect multiplication as the season progressed (Talekar andChen 1983; Kamara et al. 2010). Overall, S. derogata and N. viridula in terms ofdensities were the most dominant and perhaps also the most damaging defoliatorand PSB, respectively, in the field. Nezara viridula has been reported as a pest ofworldwide economic importance and the most damaging pest in soybean (Musser

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Table

3.

Effectofinsecticideapplicationtimingoninsect

pests’densities,damageandyield

ofsoybeanatNyankpala,2009.

Insecticideapplication

timing

No.of

defoliators

m7

1Defoliation

(%)

No.of

pod

bugsm

71

Seed

damage

(%)

Grain

yield

(kgha7

1)

Yield

loss

(%)

Control

0.9+

0.1

a20.3+

0.8

a1.0+

0.2

a10.3+

2.3

a1008.9+

17.7

b42.8+

4.2

aVegetativestage

0.8+

0.1

a11.0+

0.5

b0.4+

0.1

b11.5+

1.7

a1161.5+

73.0

b34.3+

5.6

aReproductivestage

0.7+

0.1

a19.1+

0.5

a0.3+

0.1

bc

5.3+

0.9

b1564.3+

85.0

a11.3+

8.0

bComplete

protection

0.4+

0.0

b9.9+

0.3

b0.1+

0.0

c5.3+

0.9

b1793.3+

124.0

a–

F6.33

108.12

28.20

4.17

21.23

36.50

p0.0135

50.0001

50.0001

0.0416

0.0002

0.0004

Values

are

means(þ

SE)offourreplicates.Within

columns,means(+

SE)followed

bythesameletter

donotdiffer

significantly(A

NOVA,p4

0.05,Fisher’sProtected

LSD

meanseparation).–,blank.

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et al. 2011). The present study, however, considered the insects along two damageguilds as defoliators and pod feeders and did not isolate the effects of individualinsects.

Insecticide treatment lowered insect densities and damage resulting in increasedyield over untreated control. This showed that insect infestations and damage limitedyield in soybean in this study, as was also reported in Nigeria by Anyim (2003).Averaged over all three years, yield loss in untreated plots was as high as 32%. Insectpests caused up to 48% yield loss in soybean in some parts of Nigeria (Anyim 2003).The yield increase with insecticide treatments, however, varied among thetreatments. The increase was highest when plots were given complete insecticideprotection or protected at the reproductive stage. A treatment at the vegetative stagedid not always increase yield over untreated control. These results demonstrated thatcontrol of insect pests at the reproductive stage was crucial for increased soybeanyields in Ghana.

A correlation analysis provided further evidence of the relative importance of thetwo distinct insect pest guilds as far as their effect on yield was concerned. Grainyield was always negatively related to the numbers of PSBs and their damage to podsand seeds, whereas yield was only negatively affected by the numbers of defoliatorsand percentage defoliation together in one out of the three years of the study. Again,this showed that although defoliators were important, PSBs that attack pods at thereproductive stage were the most damaging insect pests of soybean in Ghana. Similarfindings were reported in Nigeria by Jackai et al. (1988). Pod-sucking bugs’ attack topods result in pod and seed abscission as well as seed shrivelling and decay (Jackaiand Singh 1987; Gore et al. 2006). Plants may have enough time to compensate forearly season insects’ attack by defoliators. However, the compensatory ability islimited during the reproductive stage, such as during podding due to senescence(Hunt et al. 2010). Gore et al. (2006) observed that early sown soybean escaped peakPSB populations and damage during podding. Also, Sastawa et al (2004) reportedthat early sown soybean recovered from insect defoliation and/or compensated forpod damage to produce high grain yield. Thus, in addition to insecticide control,early sowing could be used to manage insect pests in soybean. These managementtactics could also be integrated with other pest management tactics, such as the use

Table 4. Correlation coefficients (r) and probabilities (p) between soybean yield and numberof insect defoliators, percentage defoliation, number of pod-sucking bugs, percentage poddamage and percentage seed damage in 2007–2009.

Yield (kg ha71)

2007 2008 2009

No. of defoliators 70.87 70.15 70.7350.0001 0.5723 0.0012

Percentage defoliation 70.83 70.50 70.4050.0001 0.0500 0.1255

No. of pod-sucking bugs 70.76 70.64 70.720.0006 0.0071 0.0018

Percentage pod damage 70.68 70.81 –0.0038 0.0001 –

Percentage seed damage 70.69 70.68 70.600.0030 0.0041 0.0148

–, data not available.

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of resistant soybean cultivars for a more sustainable control. Jackai et al. (1988)reported a field resistance of some soybean cultivars or breeding lines to soybeanbugs.

In conclusion, the results from this study suggested that PSBs were the mostdamaging and important insect pests of soybean in Ghana. Thus, insecticideprotection against insect pests in soybean in Ghana should be targeted at thereproductive stage for the control of PSBs. This is particularly important for theresource-poor farmers who cannot afford complete insecticide protection for theircrops. The insecticide control could also be combined with other pest controloptions, such as the use of insect resistant soybean cultivars and early sowing for amore sustainable control of insect pests in soybean.

Acknowledgements

The authors thank Frederick Anaman, Soweiba Abdulai and Kwabena Yaw James fortechnical assistance and all the labourers at the Entomology section of CSIR-SavannaAgricultural Research Institute for field work.

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