An integrated approach to pest management in field pea, Pisum sativum (L.), with emphasis on pea aphid, Acyrthosiphon pisum (Harris)
Loading...
Date
2002-03
Authors
Ahmed, Kemal Ali
Journal Title
Journal ISSN
Volume Title
Publisher
University of the Free State
Abstract
This study comprises investigations into pea aphid, Acyrthosiphon pisurn, and ascochyta
blight damage on field pea, the evaluation of plant resistance levels in both breeding lines
and cultivars, the identification of plant resistance and the underlying mechanisms, and
cultural, chemical and biological control methods. Varietal resistance studies indicated that
there were differences between the Ethiopian and the South African strains of pea aphid with
regard to their survival and reproduction on the field pea genotypes evaluated. The field pea
entries performed very well against the former strain compared with the latter. Three lines
(Holetta Local-90, 305PS210687 and 061K-2P-2/9/2) performed well across both strains.
Field pea lines exhibiting tolerance, antixenosis and antibiosis resistance to A. pisum were
identified under greenhouse conditions. Some lines showing high levels of antibiosis to
nymphal feeding were also found in both strains. This kind of resistance mechanism may
promote insect biotype development through increased selection pressure on the pest
population. Strain variation was also evident in tolerance, antixenosis and antibiosis
resistance. The South African strain was the least aggressive across all entries. Of the 30
varietiesllines (including a local susceptible cultivar from Ethiopia) evaluated for resistance
to isolates of Mycosphearella pinodes, Oregon Sugar Pod II had a 1.9 blight severity and was
scored as resistant, three genotypes (Green Feast, Sugar Queen and line 304WAll01973)
were scored as intermediate (2.1 - 3.0 severity factor) and the remaining 26 genotypes were
scored as susceptible (3.1 - 4.0 severity factor) or highly susceptible (4.1 - 5.0 severity
factor). In all scoring dates, significant differences occurred among genotypes, isolates and
genotype x isolate interactions. However, the genotype x isolate interaction contribution to
total variation was much lower than that of genotypes and isolates separately. The isolate of the Denbi site in Ethiopia was slightly more virulent than those of the Holetta and Kulumsa
sites. Assessments regarding the potential of biological control of pea aphids using a
predatory beetle (Hippodamia variegata) and entomopathogenic fungus (Beauveria
bassiana) indicated that predator-treated plots supported significantly lower aphid numbers
from the third week onwards, when compared to the fungus-treated and infested control
plots. The degree of mycosis caused by Beauveria on pea aphids was 14.3% in week three
after inoculation and the figure dropped to 2.5% in week 5. Percentage yield loss due to pea
aphid in predator-treated plots was 8.3 % compared with 16.0 % in fungus-treated plots.
Field pea intercropped with Ethiopian mustard sustained less pea aphid and ascochyta blight
incidence, compared to faba bean, wheat and field pea mono crop at all locations studied. The
land equivalent ratio for this particular mixed crop system exceeded 1.0, indicating that the
mixed crops selected were efficient for yield and monetary outcome. The increase in
efficiency was ascribed to the barrier effect of mustard plants in the intercrop set-up, which
was significant in reducing pea aphid population size and disease severity. The effect of
fertilizer application and sowing date on pea aphid and ascochyta blight severity was location
specific. At the Holetta site in Ethiopia disease severity and pea aphid infestation were
significantly reduced in fertilized plots compared with unfertilized plots, while it was only
the disease that showed significant difference at the Denbi and Kulumsa sites. This indicates
the importance of fertilizer application as a cultural control strategy for this disease. Neither
early nor late sowing resulted in reduced aphid infestation and disease infection at any of the
locations. Significant interactions between variety, sowing date and fertilizer for ascochyta
blight was observed, indicating that the effect of one factor was influenced by the other two
factors. For aphid population density and yield, the three factors had little or no effect on
each other at the Denbi and Kulumsa sites. Cultivar Markos was moderately resistant to
ascochyta blight and it gave higher yield compared to Mohanderfer and the varieties used by
farmers. Neem seed kernel extract application was superior to Multineem", a commercial
product, against pea aphid development and reproduction. The neem preparations
significantly reduced the number of molts, longevity and fecundity of A. pisum in a
concentration-dependent manner. The effect on young adults exposed to neem was not as
drastic as in the case of immatures. Acute and chronic toxicity effects on pea aphid were
noted showing that azadirachtin is an effective inhibitor of population growth of pea aphid
both on treated plants and when topically applied to the insect. Host plant resistance and
natural chemical (neem) pest control in large scale farming systems, or integrated with
cultural and biological control in low-input subsistence farming systems provides effective
management strategies for pea aphid and ascochyta blight in field pea. From this study,
possible implementation of IPM in field pea is presented and includes aspects of varietal
resistance and biological, cultural and chemical control.
Description
Keywords
Peas -- Diseases and pests, Pests -- Control, Agricultural pests -- Integrated control, Thesis (Ph.D. (Zoology and Entomology))--University of the Free State, 2002