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African Crop Science Journal
African Crop Science Society
ISSN: 1021-9730 EISSN: 2072-6589
Vol. 6, Num. 4, 1998, pp. 351-356
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African Crop Science Journal, Vol
African Crop Science Journal, Vol. 6. No. 4, pp. 351-356,
1998
Printed in Uganda. All rights reserved
©1998, African Crop Science Society
Some Cultural Strategies For Management Of
Bean Stem Maggots (Diptera: Agromyzidae) On Beans In
Tanzania
J.K.O. Ampofo and S. M. Massomo
SADC/CIAT Regional Programme on Beans in Southern Africa,
P.O. Box 2704, Arusha, Tanzania
(Received 16 June, 1998; accepted 8 September, 1998)
Code Number:CS98037
ABSTRACT
We compared cultural practices commonly used in bean
(Phaseolus vulgaris L.) and other vegetable cropping
systems to assess the effect of individual as well as combinations
of practices on bean stem maggot (BSM) (Ophiomyia spp.
Diptera: Agromyzidae) infestation and subsequent damage to bean
plants. The cultural practices used included mulching, application
of fertilizer and chemical seed dressing. Chemical seed dressing
reduced pest incidence during early growth stages and enhanced
plant survival. Mulches and application of fertilizer did not
reduce pest infestation but enhanced plant tolerance to the pest;
it also reduced subsequent plant mortality compared to the control.
Combinations of these practices were even more effective in
reducing BSM induced plant mortality and increasing crop yield.
Their efficiencies varied with location.
Key Words: common bean, (Phaseolus vulgaris), bean
fly (Ophiomyia spp.), cultural control, mulches
RÉSUMÉ
Des pratiques culturarles communément
utilisées dans les systèmes de culture du haricot
(Phaseolus vulgaris L.) et d'autres
végétaux ont été comparées pour
évaluer l'effet des pratiques individuelles ou
combinées sur l'infestation de la mouche du haricot
(Ophiomyia spp. Diptera: Agromyzidae) et les
dégâts causés aux plants du haricot. Les
pratiques culturales utilisées comprenaient le paillage,
l'application des engrais et le traitement des semences. Comme
attendu, le traitement des semences avec les produits chimiques a
réduit l'incidence de la mouche au début des stades
de croissance et a augmenté la survie des plants. Les
paillages et l'application des engrais n'ont pas réduit
l'infestatuion de la peste mais ils ont, au contraire,
augmenté la tolérance à la mouche et
réduit la mortalité des plants par rapport au
contrôle. Les combinaisons de ces pratiques étaient
encore plus efficaces en réduisant la mortalité des
plants induite par la mouche du haricot et en augmentant le
rendement en graines. Cependant, leur efficacité variait
avec le milieu.
Mots Clés: haricot commun, Phaseolus
vulgaris, larve de la mouche du haricot, mouche du haricot
(Ophiomyia spp.), contôle cultural, paillages
Introduction
Over 80% of beans in sub-Saharan Africa are grown in
marginal environments where soils are impoverished, but little
external inputs are used to improve crop growth. In these regions
beans are traditionally grown by small-scale farmers. Their land
sizes often do not exceed 1 ha and as such do not rotate crops or
allow fallow periods. This leads to a build up of pest and
diseases. Bean stem maggot (BSM), also known as bean fly
(Ophiomyia spp., Diptera: Agromyzidae), is the most
important pest of beans in such systems; the insect is also the
principal pest of beans in Asia and Oceania (Le Pelley, 1959;
Greathead, 1968; Talekar, 1990). Three species which attack beans
have been recorded from Africa. These are: O. phaseoli
Tryon, O. spencerella Greathead and O.
centrosematis (de Meij.). The adult oviposits in leaves, stems
and hypocotyl of young seedlings. Emerging maggots mine their way
to the root collar where feeding becomes concentrated between the
woody stem and the epidermal tissue. Such feeding interfere with
nutrient transport and creates avenues for the entry of disease
organisms.
BSM damage is most severe and often leads to mortality when
seedlings are attacked. Older plants are able to survive the attack
better, but become stunted and yields are depressed. In plants
under stress, such as may result from soil infertility or drought,
BSM attack may lead to a total crop failure. Losses in the range of
30-100% are frequently reported in Africa (Greathead,1968; De Lima,
1983; Autrique, 1985; Karel and Matee, 1986).
Current control recommendations rely on chemical pesticides
applied as seed dressings before sowing, or foliar sprays soon
after plant emergence (Lays and Autrique, 1987). These applications
may effectively control the pest but many of the recommended
chemicals are banned (e.g. endosulfan and lindane), or are too
expensive or un available (e.g. abamectin) to the average small-
scale bean grower in Africa. Sustainable control approaches for
such farmers must lean on tactics and/or products that can be
regenerated within the farming environment. Such tactics include
cultural methods used in the production of other crops, host plant
resistance and use of plant extracts with insecticidal properties.
Cultural practices are used by farmers to escape pest infestations,
enhance crop growth and promote tolerance to infestation or reduce
suitability of the environment for rapid population development. In
this study, we tried to quantify the effect of certain cultural
methods on BSM infestation and damage to bean plants.
Materials and Methods
Field studies were conducted in the 1992 and 1993 short
growing seasons at two locations in northern Tanzania: Sinon in
Arusha District and Mabughai in Lushoto District. These sites
differ in soil fertility, the latter being less fertile, a
parameter which also affects plant ability to tolerate BSM
damage.
Land preparation was by ox-plough at Sinon and by a forked hoe
at Mabughai. At both locations, the field was leveled before
sowing. Sowing was done in furrows about 3 cm deep, at 15 cm apart,
and covered. Plot size was 9 rows spaced at 50 cm apart and 5 m
long. This gave a population of 134, 000 plants ha-1. Such low
plant populations favour BSM infestation (Abate, 1990) and were
used in the trials to enhance infestation.
Fertiliser application treatments were made to their respective
plots before sowing. Mulch was applied immediately after sowing.
The trial was laid out in a randomised complete block design. The
common bean variety "Lyamungu 85" was grown. Moisture was limiting
during the cropping period at both locations, but at Sinon this was
reduced by the application of supplemental furrow irrigation.
Cultural methods tested were:
1. Enhanced soil fertility (F): additional organic fertilizer
applied at sowing and side dressing at 30 kg P2O5 and 60 kg N per
ha.
2. Mulches (M): the spreading of dry banana leaves (in Sinon)
or dry bracken fern leaves (at Mabughai) to a layer approximately 4
cm thick over the plots after sowing.
3. Endosulfan seed dressing (E) at 5 g of endosulfan 47%
mixed in a slurry with 1 kg of wetted seed before sowing.
4. Control (C) (seeds sown on the flat without the
application of any of the above)
5-8. Various combinations (M+F, M+SD, F+SD and M+F+SD) of the
individual treatments were applied.
The plots were weeded. Data were collected on plant emergence,
plant mortality due to BSM as well as other mortality factors, and
agronomic performance indices such as vigour, dry matter
accumulation and grain yield. All dead plants in each plot were
counted and removed on each sampling occasion. They were then
examined for cause of mortality (i.e. mechanical damage, disease
induced mortality, BSM induced mortality and others). BSM infested
plants were dissected to estimate the levels of infestation and the
composition of the prevailing BSM species. The data were subjected
to ANOVA as distinct treatments and means were compared using the
SNK procedure.
RESULTS
BSM infestation and subsequent plant mortality were higher
at Mabughai than at Sinon. At Mabughai, BSM infestation levels in
the non-endosulfan treated plots ranged between 9 and 12 insects
per plant; plant mortality levels ranged from 81 to 232 plants per
plot (34 and 95 % of total plant population, respectively) (Table
1). Infestation and subsequent plant mortality in the endosulfan
treated plots were significantly (P<0.05) lower. This trend was
repeated at Sinon but the differences were non-significant (Table
2). BSM infestation levels were the highest at about 3 weeks after
plant emergence (WAE) at Mabughai (Table 1). Infestation at
flowering (6 WAE) or later followed no definite pattern. This may
be due to the inability of endosulfan to deter BSM infestation as
endosulfan concentrations in the plant tissues at this stage may be
sublethal (less than 0.5 mg/kg) (Autrique, 1989). While
infestations at flowering or later developmental stages may
interfere with nutrient transport and cause stem weakening and
subsequent lodging, they do not cause plant mortality directly.
TABLE 1. Effect of various cultural
practices on BSM infestation and subsequent mortality caused to
bean plants (Mabughai, Lushote District, 1993)
Treatment |
BSM/5 plants at 3 WAE |
BSM/Infested plant at 6 WAE |
Cum. plant mortality due to BSM |
C |
9.0 ab |
4.5 a |
232.0 a |
F |
11.0 a |
8.4 a |
189.3 b |
M |
12.0 a |
7.3 a |
127.3 c |
E |
3.5 ab |
2.3 ab |
6.0 bc |
EM |
10.8 a |
5.6 a |
33.7 e |
EF |
3.4 bc |
3.9 a |
22.0 e |
MF |
11.6 a |
9.1 a |
80.7 d |
EMF |
0.6 c |
3.9 a |
10.7 e |
LSD (0.05) |
6.3 |
5.3 |
29.2 |
Means within a column followed by the same letter are not
significantly different at P<0.05 (according to the SNK Range
Test); WAE = weeks after emergence; C- Control; E- Endosulfan seed dressing; F- Fertiliser; M- Mulch;EF- Endosulfan plus fertiliser; EM- Endosulfan plus mulch; MF-mulch plus fertiliser and EMF- Endosulfan, mulch and fertiliser
Among individual non-endosulfan treatments, mulch and fertiliser
reduced plant mortality significantly (P<0.05) below that
of the control at Mabughai (Table 1). Mulch also delayed mortality
but did not reduce BSM infestation. However, all the treatment
combinations (including M+F) reduced plant mortality below that of
endosulfan alone at Sinon (Table 2). Plant mortality was
significantly correlated with BSM infestation at 3 WAE (r2 = 0.47,
P<0.01).
TABLE 2. Effect of various cultural
practices on BSM infestation and subsequent plant mortality (Sinon,
Arusha, 1992/93 short rainy season)
Treatment |
Infested plants |
BSM/infested Plant |
Cumulative Plant Mortality due to BSM |
C |
4.5 a |
2.0 ab |
22.0 a |
F |
4.5 a |
2.1 ab |
13.5 ab |
M |
4.0 ab |
3.1 a |
13.5 ab |
E |
3.5 ab |
2.3 ab |
6.0 bc |
EM |
2.5 bc |
2.2 ab |
1.5 c |
EF |
2.5 bc |
2.7 ab |
1.5 c |
MF |
3.5 ab |
3.7 a |
1.5 c |
EMF |
1.0 c |
1.0 b |
0.0 c |
LSD |
1.7 |
1.7 |
11.7 |
Sample (5 plants) at flowering
Means within a column followed by the same letter are not
significantly different at P<0.05 (according to the SNK Range
Test)
C- Control; E- Endosulfan seed dressing; F- Fertiliser; M- Mulch;
EF- Endosulfan plus fertiliser; EM-Endosulfan plus mulch; MF- mulch
plus fertiliserand EMF- Endosulfan, mulch and fertiliser
None of the treatments had any significant effect
(P<0.05) on plant establishment at emergence even though
enhanced fertility, mulch, and M+F appeared to improve it (Tables 3
and 4). Also, the combined treatments of mulch and enhanced
fertility (M+F and E+M+F) increased plant vigour as measured by
canopy height and canopy width at flowering (Table 4). Fertiliser
treatment enhanced plant tolerance to infestation and positively
influenced yield parameters such as pods per plant and overall seed
yield, especially at Mabughai (Table 3) where the soil was
generally infertile. At this site, the highest yielding treatments
were EMF, MF and EF. These were significantly (P<0.05)
different from all other treatments but not from each other.
TABLE 3. Effect of various cultural practices on bean
plant performance and yield (Sinon 1992/1993 short rainy
season)
Treatment |
Stand at emergence |
Plant vigour at flowering |
Total dry matter in gm/5 plants at
flowering |
Plant stand at harvest (No. of plants) |
Pods/plant |
Seed yield in kg ha-1 |
Canopy height (cm) |
Canopy width (cm) |
C |
282.2 b |
36.5 c |
18.0 bc |
48.0 a |
225.2 b |
14.14 a |
1239.0 c |
F |
317.5 ab |
37.5 bc |
19.5 b |
44.0 a |
221.0 b |
13.04 a |
1355.0 bc |
M |
312.5 b |
32 5 c |
14.5 c |
23.0a |
219.0b |
10.89a |
1132.0c |
E |
283.0 b |
38.0 bc |
18.0 bc |
41.5 a |
243.2 ab |
14.64 a |
1699.0 abc |
EM |
294.5 b |
38.5 bc |
18.0 bc |
36.5 a |
239.2 ab |
13.65 a |
1599.0 abc |
EF |
307.7 b |
35.5 c |
16.5 bc |
37.5 a |
230.5 ab |
13.39 a |
1243.0 c |
MF |
360.5 a |
45.0 a |
25.0 a |
39.0 a |
253.2 a |
14.02 a |
2034.0 a |
EMF |
320.5 ab |
43.0 ab |
19.5 b |
46.0 a |
243.0 ab |
14.27 a |
1931.0 ab |
LSD (0.05) |
44.1 |
6.0 |
4.4 |
24.0 |
23.7 |
6.2 |
645.0 |
Means within a columnn followed by the same letter are not
significantly different at at P<0.05 (according to the SNK Range
Test)
C- Control; E,, Endosulfan seed dressing; F- Fertiliser; M- Mulch;
EF- Endosulfan plus fertiliser; EM- Endosulfan plus mulch; MF-
mulch plus feniliser and EMF Endosulfan, mulch and feniliser
TABLE 4. Effect of various cultural practices on bean
plant performance and yield, (Mabughai 1993)
Treatment |
Plant Stand at: |
Pods/plant |
Seeds/pod |
Seed yield in kg ha-1 |
Emergence |
Harvest |
C |
248.0 a |
36.5 e |
3.42 c |
2.90 c |
25.4 c |
F |
247.7 a |
75.7 d |
7.35bC |
4.10a |
123.8bc |
M |
242.7 a |
105.8 d |
5.40 bc |
3.57 ab |
173.9 bc |
E |
240.0 a |
216.8 ab |
5.42 bc |
3.32 bc |
266.4 b |
EM |
238.2 a |
183.8 bc |
5.97 b |
3.75 ab |
314.9 b |
EF |
237.2 a |
218.0 ab |
9.60 a |
3.97 ab |
576.8 a |
MF |
2~3.5 a |
165.3 c |
8.62 a |
4.02 a. |
585.2 a |
MF |
242.2 a |
230.0 a |
8.87a |
4.12a |
776.8a |
LSD (0.05) |
26.4 |
36.8 |
2.5 |
0.65 |
201.8 |
Means within a column followed by the same letter are not
significantly different at P<0.05 (according to the Duncan's
Multiple Range Test)
C- Control; E- Endosulfan seed dressing; F- Fertiliser; M- Mulch;
EF- Endosulfar plus fertiliser; EM- Endosulfan plus mulch; MF-
mulch plus fertiliser and EMF- Endosulfan, mulch and fertiliser
DISCUSSION
BSM species composition was similar at both sites, with
O. spencerella being dominant (>80% of total population).
BSM infestation and its associated plant mortality was higher at
the less fertile environment (Mabughai) than at the relatively more
fertile environment (Sinon). The effect of enhanced soil fertility
on the ability of bean plants to tolerate BSM attack was
demonstrated by Autrique (1989). Possibly, because of the higher
soil fertility at Sinon, the effect of the additional fertilizer
application was not as pronounced as in Mabughai. At Mabughai,
treatments with enhanced soil fertility reduced plant mortality and
increased yield (mean fertilizer treatments 517.4 kg ha-1 compared
with treatments without fertilizer of 194.5 kg ha-1). This effect
was also reflected in other agronomic parameters associated with
yield (e.g. pods per plant) but not in reductions in BSM
infestation levels. Fertiliser combined effectively with most of
the other treatments to reduce plant mortality beyond that of
fertilizer or mulch alone, in spite of the fact that both
treatments failed to reduce BSM infestation levels. This implies
that fertilizer applications or soil fertility status per se
does not protect plants against BSM infestations, but improves the
plants' ability to tolerate the infestation.
Farmers use a variety of traditional methods to manage pests,
diseases and other constraints in crop production systems. In many
instances, one strategy may have diverse benefits to the crop.
Mulches are generally considered to improve soil and water
conservation and to help control weeds (Ackland, 1971; IITA, 1992).
Grass mulch is used routinely by vegetable growers in Lushoto
District to conserve moisture. Ngoli and Tarimo (1985) observed no
direct significant effect on bean yield in Tanzania, but in Malawi,
Letourneau (1994) observed a reduction of BSM infestation and
subsequent plant damage in mulched plots. In the present trial,
mulching increased yield seven times above that of the control at
Mabughai possibly because of low pest incidence and more fertile
soils at this site. The combination of mulch plus fertiliser was
among the best two treatments tested (including treatments with
endosulfan seed dressing) in terms of grain yield at both
locations, and doubled the yield over that of chemical seed
dressing. This treatment combination did not reduce BSM infestation
per se, it appeared to promote plant vigour and tolerance to
attack and reduced plant loss resulting from infestation and
damage. Mulches are reported also to reduce bean infections by web
blight (Galindo et al., 1983) which may also aggravate the
BSM problem.
In our trials, we have used the most common mulching material in
either environment. However, because of the additional labour
requirement in the carting of mulching material to the bean fields
and the competition between this and use of potential mulch
material for animal feed, this procedure is unlikely to be readily
adopted by farmers for field production of beans. However, in
certain production systems such as rice and other small grains,
where excess straw becomes available after harvest, this management
approach may be suitable on a large scale. In Costa Rica, farmers
overcome the lack of availability of mulch material by broadcasting
beans through weeds and cutting the weeds to cover them, a practice
known as "frijol tapado" (Galindo et al., 1983). The
practice reduces the labour cost that may be incurred in carting
mulch material. Another amendment in the form of direct mulch
practice would be through the use of herbaceous N-fixing legumes
e.g. Mucuna puriens, various species of Crotalaria
and Pseudovigna argentea which have been shown to have
adequate nitrogen fixing abilities as well as biomass production
for mulches (IITA, 1992). The use of these N-fixing legumes would
provide the required N and mulch material to enhance bean plant
tolerance to BSM attack.
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Copyright 1998, African Crop Science Society
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