Advantages and limitations in bioherbicides use

Advantages and limitations in bioherbicides use
Advantages and limitations in
bioherbicides use
Zvonko Pacanoski

Limitations of bioherbicides:
- biological constraints
- environment constraints
- technical constraints and
- commercial limitations
Bioherbicides
phytopathogenic microorganisms or
microbial phytotoxins useful for biological
weed control applied in similar ways to
conventional herbicides (Goeden, 1999;
Boyetchko et al., 2002; Boyetchko and
Peng, 2004)
Bioherbicides serves a more important role as a complimentary
component in successful integrated management strategies
(Hoagland et al., 2007), and not as a replacement for chemical
herbicides and other weed management tactics (Singh et al., 2006)
Advantages of bioherbicides:
high degree of specificity of target weed;
no effect on non-target and beneficial plants or man;
absence of residue build-up in the environment;
effectiveness for managing herbicide-resistant (HR) weed populations

Successful stories about bioherbicides
commercialized
bioherbicides
200 plant pathogens
candidates for development as
commercial bioherbicides
Plectosporium tabacinum
Galium spp.

Colletotrichum truncatum
Sesbania exaltata
Fusarium oxysporum (PSM 197)
S. asiatica (91.3%) S. hermonthica (94.3%) S. gesneroides (81.8%)

Myrothecium verrucaria (IMI 361690)
Chenopodium
amaranticolor
Sesbania exaltata Senna obtusifolia Datura stramonium
Trichothecene
Orobanche ramosa seeds

Myrothecium verrucaria
Portulaca oleracea
Portulaca
portulacastrum
Euphorbia maculata Euphorbia prostrata
Phomopsis amaranthicola
Amaranthus spp.

Microsphaeropsis amaranthi Phomopsis amaranthicola Amaranthus spp.
Pyricularia setariae Setaria viridis sethoxydim
Colletotrichum truncatum
Sesbania exaltata

Dactylaria higginsii
Cyperus routndus
Drechslera avenacea
Avena fatua

Synergism between bioherbicides
and chemical herbicides
Combinations of some bioherbicides and synthetic herbicides can be
synergistic (Caulder and Stowell, 1988; Christy et al. 1993), resulting
from lowered weed defense responses caused by the herbicides, thus
making the weeds more susceptible to pathogen attack (Hoagland, 1996;
2000).
Synergism
trimethylsulfonium salt of glyphosate
Xanthomonas campestris

Fusarium lateritium
Desmodium tortuosum
Alternaria cassiae
Senna obtusifolia
acifluorfen
Colletotrichum gloesporioides Aeschynomene virginica
Synergism
Colletotrichum truncatum
Sesbania exaltata
bentazon

Glyphosate
Synergism
Myrothecium verrucaria
Brunnichia ovata (88%) Campsis radicans (90%)

Phoma proboscis
Synergism
2,4-D
MCPP
MCPP
Convolvulus arvensis
yrothecium verrucaria Silwet L-77 Pueraria lobata
(100 and 90-100%)

Different limitations about bioherbicides use
1. Environmental limitations
Environmental factors influence formulation performance of bioherbicides as
inoculum production is dependent on sporelation of the formulation.
In the application of bioherbicides, environmental conditions prevailing in
the phyllosphere of plants are frequently hostile for biological control
agents (KENERLEY & ANDREWS, 1990; ANDREWS, 1992).
phyllosphere of plants
A requirement for more than 12 h of dew period for severe infection by a
pathogen, has been reported for several potential bioherbicides (BOYETTE
& WALKER, 1985; WYMORE et al., 1988; MORIN et al., 1990; MAKOWSKI,
1993) and this may limit the efficacy of the bioherbicide in the field.
dew period

Soil
environment
Soil moisture
Nutrient status of the
soil
physiology of target plants
Colletotrichum truncatum Sesbania exaltata (95%)

Biological limitations
It is desirable for a bioherbicide to act relatively quickly and have sufficient
efficacy to control weeds. Unfortunately, many of the weed pathogens
discovered may provide only partial control of only one weed species, even under
ideal conditions (CHARUDATTAN, 2005).
Host specificity is related to the basic biology of the pathogen and to host
variability (GABRIEL, 1991; LEONARD, 1982). Biological constraints including
host variability and resistance, as well (AULD, 2003).
?
Chondrostereum purpureum
Prunus serotina

Colletotrichum orbiculare
Xanthium spinosum
Technological-commercial limitations
Several technological limitations have been identified that could prevent the
widespread use of bioherbicides
Pathogenical strains, formulation method and the interaction of these two
parameters significantly affect the shelf life of the formulations at room
temperature (ALTMAN et al., 1990; HEBBAR et al., 1998).
The most challenging aspect of formulating bioherbicides is to overcome the dew
requirement that exists for several of them.
water-retaining materials
invert emulsion
vegetable oil emulsion

spray drying process Phomopsis sp. Carthamus lanatus
Alternaria eichhorneae
alginates
liquid formulations
of bioherbicides
gellan gum
polyacrylamide

Conclusion
The bioherbicides approach is gaining momentum
New bioherbicides will find place in irrigated lands, wastelands as well
as in parasite weeds or resistant weed control
Research on synergy test of pathogens and herbicides for inclusion in
IWM, developmental technology, fungal toxins, and application of
biotechnology, especially genetic engineering is required
Bioherbicides will not solve all of the environmental and weed
management problems associated with synthetic herbicides, nor will
replace the current or future arsenal of synthetic herbicides
Their role will probably be complimentary components in successful IWM
systems, and in the discovery of novel phytotoxins with new chemistries
and new molecular sites of action
Continued research on these areas is important in order to fully
understand interactions of microorganisms and plants (crops and
weeds), and to discover new phytopathogenic microorganisms or
microbial phytotoxins useful as bioherbicides

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