Evaluation of the potential use of antagonistic microbes on grass species, turf and pasture, for disease control and growth stimulation.
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Date
2003
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Abstract
Public tendency, of late, is to reduce liberal use of harmful synthesized chemicals for
promoting plant health. Today, biological control is becoming a commonly cited disease
control option. Biological control agents (BCAs) not only control disease , but also
promote plant growth. Application of biological control is based largely on knowledge of
control mechanisms employed by antagonists, as well as the means of application that
will ensure that an antagonistic population is established. Knowing the advantages is not
the only factor that should be considered before application commences as, the
disadvantages must be clearly outlined and explored further before a constructive
decision as on implementation of biological control. A literature review was undertaken
to provide the necessary technical information about biological control, its potential uses,
methods of application, mechanisms of action employed, advantages and disadvantages
associated with biological control application, public perceptions and the potential future
of biological control.
Diseases encountered within the KwaZulu-Natal Midlands on pasture and turf grasses
were determined by a once-off survey conducted over 1999/2000. The aim of the survey
was to determine broadly the management practices of farmers and groundsmen in
KwaZulu-Natal and the potential impact of these on the occurrence of weeds, insects and
diseases. The survey also addressed the level of existing knowledge about biological
control and willingness to apply such measures. In the pasture survey, farmers were
questioned about: soil type, grass species common used, irrigation , fertilization and
liming, grazing programs and weed, insect and disease occurrences and control
measures implemented. The same aspects were addressed in a survey to a
representative sample of groundsmen (turfgrass production) , including also: topdressing,
greens base used, drainage systems, mowing practices and decompaction principles.
The survey showed correlation between pest incidence and management practices
implemented. In terms of pest control, both farmers and groundsmen indicated a stronger
preference to the use of herbicides , insecticides and fungicides. Use of fungicides for
disease control by farmers is considered an often unfeasible expense, rather more
emphasis was placed on implementing cultural control methods. At present farmers do
not apply biological control strategies, but they did indicate much interest in the topic.
Alternatives to current, or lack of current, disease management strategies are important
considerations, with two new diseases identified in the KwaZulu-Natal Midlands just
within the period of this thesis. Biological control strategies are implemented by 8% of the
groundsmen surveyed, with emphasis being placed on augmenting the already present
natural predators rather than the introduction of microbial antagonists.
Although often mis-diagnosed by farmers Helminthosporium leaf spot is a common
disease in the KwaZulu-Natal Midlands on Pennisetum clandestinum (kikuyu), This
disease reduces pasture quality and detracts from the aesthetic appearance and
wearability of turfgrasses. Helminthosporium leaf spot is incited by a complex of causal
agents , Bipolaris was confirmed as the casual agent of Helminthosporium leaf spot on
kikuyu at Cedara. Disease control by two BCAs, Bacillus (B. subtilis Ehrenberg & Cohn.)
and Trichoderma (T. harzianum Rifai), as commercial formulations was tested against
the fungicide, PUNCH EXTRA®. In vitro, Trichoderma was shown to be aggressive in
controlling Bipolaris sp. In vivo, disease control achieved with Trichoderma kd was
comparative with PUNCH XTRA® but not statistically different (P>=0.05). Trichoderma and
Bacillus provided better disease control in comparison to an untreated control.
Improved growth of Lolium sp. was determined in vitro, with Trichoderma kd and Bacillus
B69 treatments. The microbe-based treatments accounted for growth stimulation, with
significant (P<=O.05) growth differences noted. A microbial activator, MICROBOOST®was
added to the treatments to improve microbial efficiency. Improved plant growth with
MICROBOOST® applications was shown.
Improved growth associated with microbial treatments, Trichoderma harzianum kd;
Bacillus subtilis B69 and Gliocladium virens Miller, Gibens, Foster and con Arx. ,was also
determined in vivo at Cedara, on L.perenne L., Festuca rubra L. and Agrostis stolonifera
L. Establishment of a suppressive soil with antagonistic microbes resulted in significant
(P<=O.05) effects on final grass coverage (except G. virens), as well increased root and
shoot lengths (P<=O.05). Increased germination rates, as expressed in vitro, were not
shown in vivo. Microbial activity with the application of MICROBOOST® showed little
effect on germination but increased root and shoot lengths significantly (P<=O.05).
Increased weed growth associated with the treatments (except G. virens) was considered
a drawback of the microbial-treatments.
Microbial treatments were also applied to pasture grasses. An in vitro grazing trial was
established at Cedara, using L. multiflorum L. to evaluate the microbe-based treatments
Trichoderma kd, Bacillus B69 and G. virens for improved pasture establishment and for
increased grazing preference by Dohne Merino sheep. Trichoderma kd was associated
with increased dry and wet biomass , but lower dry matter yields in comparison to the
control. Only G. virens accounted for a higher dry matter percentage than the control.
However, differences between the control and the microbial treatments was very small
and not significant (P>=0.05). Of the three grazing observations made, sheep showed no
grazing preference to plots with or without microbial treatments
In general, the body of this research has shown that microbial treatments have the
potential for increased disease control and growth stimulation of grasses. However, lack
of significant differences between microbial treatments and controls has raised the
question as to effect of external factors on microbial activity and survival, especially in
vivo. This raises the question as to the validity of the use of microbial treatments where
growth conditions cannot be controlled , remembering that the cost of establishment must
be covered by the economic returns from utilization.
Description
Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 2003.
Keywords
Biological pest control agents., Grasses--Diseases and pests., Turfgrasses--Diseases and pests., Theses--Plant Pathology.