Organic farming - Bioherbicide tool for weed control

Introduction: Biological control of weeds is the use of living organisms (biotic agents) to reduce the vigour, reproductive capacity, density, or impact of weeds. The classical strategy is based on introduction of host-specific organisms from the weed’s native range into regions where the weed has established and become a widespread problem. The biotic agents, after quarantine to assure host specificity, are released into weed-infested sites and are allowed to adapt and flourish in their new habitat over time to eventually establish a self-perpetuating regulation of the weed infestation at acceptable levels. Thus, classical biological control requires a time period of one to several years to achieve adequate control while the agent population builds up to levels to impact the weed population. (Charudattan R. 2005)

The inundative strategy attempts to overwhelm a weed infestation with massive numbers of a biotic agent in order to attain weed control in the year of release. In contrast to classical biological control, inundation involves timing of agent release to coincide with weed susceptibility to the agent and formulation of the agent to provide rapid attack of the weed host. A development of the inundative strategy is the bioherbicide approach, which involves application of weed pathogens in a manner similar to herbicide applications. Since most bioherbicides have been developed using selected plant pathogenic fungi that cause such diseases on weeds as anthracnose and rust, the term mycoherbicide is often used in reference to these fungal preparations.

Need Bioherbicides

1. Yield losses still occur despite of available herbicides.

2. Herbicide resistant weed populations have developed.

     3. Herbicides may have detrimental effects on non target plants.

     4. Large areas where herbicide application not possible or not effective .

     5. Damage to the environment.

     6. Ground water contamination.

The Bioherbicide Advantage

1. Bioherbicide can be readily   integrated into weed management systems.

2. Bioherbicides are often compatible with synthetic herbicides.

3. Organically acceptable.

4. Low maintenance and management.

5. Effective area not limited.

Ideal Characteristics of a Bioherbicide

1. Produce abundant and durable inoculum in culture.
2. Target specific.
3. Genetically stable.
4. Capable of killing a significant portion of the weed population under a variety of environmental conditions. (weed densities)

Important Bioherbicides being produced and used commercially

Trade name	Mycoherbicide	Country	Weed controlled
DEVINE	Phytophthora palmivora: it is a liquid suspension & cause root rot in the weed.	-	Strangle vine (Morrenia odorata) in citrus orchard
COLLEGO	Collectotrichum gloesporiodes f.sp. Aeschynomene.: it is a wettable powder and causes stem and leaf blight in the weed.	USA	Northern join vetch (Aeschynomone spp.)
BIPOLARIS	Bipolalaris sorghicola: it is a liquid suspension	-	Johnson grass  (sorghum halepense)
BIOLOPHOS	A microbial toxin produced as fermentation product of streptomyces hygroscopicus	-	Non specific general  vegetation
BIOMAL	Wettable powder of Collectotrichum gloesporiodes f.sp. Malvae	USA	Malvapusilla
Dr. BIOSEDGE	Puccinia canooliculata	-	Cyperus esculentus
ABG-5003	Wettable powder cercospora rodmanii	USA	Water hyacinth (Eichornia crassipes)
WELCO	Collectrichum coccodes	USA	Abutilon theophrasti
LUBOA	Collectotrichum f.sp. cuscutae	CHINA	Cuscuta spp.
CASST	Alternaria cassiae	USA	Cassia obtusifolia

Steps in Bioherbicide Development

The development of Bioherbicide involves three major phases:

A) Discovery

The discovery phase involves Collection of diseased plant material:

1. Isolation of the causal organism

2. Identification of the pathogen, culture of the pathogen on artificial media

3. Maintenance of the pathogen cultures in short-term and long-term storage

B) Development

The development phase involves:

     1. Determination of optimum conditions for  spore production

2. Determination of optimum conditions for infection and disease development

3. Determination of host range and explanation of mechanism of action of the pathogen

C) Deployment

Involves close collaboration between   non industrial and industrial sectors through

1.   Formulation

2.   Scale-up

3.   Field evaluation

4.   Marketing stages of commercialization of new bioherbicide product

Some Commercial Mycoherbicides in Use Abroad

Product	Content	Weed controlled
De-vine	A liquid suspension of fungal spores of Phytophthora palmivora Butler. It causes root rot in the weed	Strangle vine (Morrenia  odorata) in citrus orchards
Collego	Wettable powder containing fungal spores of Colletotrichum gloesporiodes Penzig & Sacc. Sp. Aeschynomene	Northern joint vetch (Aeschynomone sp) in rice fields. The bioherbicide causes stem and leaf blight in the weed
Bipolaris	A suspension of fungal spores of Bipolaris sorghicola	Johnson grass (Sorghum halepense)
Biolophos	A microbial toxin produced as fermentation product of Streptomyces hygroscopicus	Non-specific, general vegetation

References

Charudattan R. (2005): Use of plant pathogens as bioherbicides to manage weeds in horticultural crops. Proc. Fla. State Hort. Soc. 118:208-214.

Daniel K. R., T. A. Bewick, L. K. Binning  and W. R. Stevenson. (1976)  Control of  weeds  with a mixture of three fungal pathogens with restricted host ranges. Biological Control  22:246-255.  

Gupta, J. M. (2001). Principles of biological weed control with micro-organisms. Horticulture Science. 32(2):201-205.

Johnson W. S., J. B. Barton, S. D. Hethering and T.S. Bellows (1996). Use of plants pathogens in weed control. Handbook of Biological Control. Pages 891-918.

Robert J. K., (2005): The role of bioherbicides in weed management Biopesticides International. 1(3, 4): 127-141.

Smith S. R., E. Rosskoff, John Wiilley (1986) Status of weed control with plant pathogens.The Biological control of Weeds Book. 3: 34-43

www.apsnet.org/online/feature/weed1

Article compiled by

Pravin B. Berad (Ph.D. Scholar)  

Dr. Panjabrao Deshmukh Krishi Vidyapeeth, Akola (M.S.)