Bioherbicides

BIOHERBICIDES

PRESENTED BY:VIKRANT MEHTAROLL NO. : 301105022

A bioherbicide is a biologically based control agent for weed. In irrigated agriculture, weed control through chemical herbicides, creates spray drift hazards and adversely affects the environment. Besides, pesticide residues (herbicides) in food commodities, directly or indirectly affect human health. These lead to the search for an alternate method of weed management, which is eco-friendly.

HISTORY OF BIOHERBICIDES

Commercial bioherbicides first appeared in the market in USA in early 1980s with the release of the products Devine ,Collego and Biomal. Devine, developed by Abbott Laboratories,USA, the first mycoherbicide derived from fungi (Phytophthora palmivora Butl.), is a facultative parasite that produces lethal root and collar rot of its host plant Morrenia odorata (stangler wine)and persists in soil saprophytically for extended periods of residual control. It was the first product to be fully registered as a mycoherbicide.

The initiative for using pathogens, phytotoxins from pathogens, and other microorganisms as biological weed-control agents began about three decades ago. Since then, numerous microbes have been screened for phytotoxic potential, and several dozens evaluated as bioherbicides as reported by various researchers and summarized (e.g., Hoagland, 1990, 2001; TeBeest, 1991). Due to the interest in this area, many other weed pathogens and phytotoxins (from pathogenic and non-pathogenic microorganisms) will be discovered that possess bioherbicidal activity. Most bioherbicides have been targeted toward agronomic weeds, but these agents may also be useful to control weeds in nonagronomic areas (recreational areas, forests, rights-of-way, lawns, gardens, etc.) where synthetic herbicides are not registered, or where their use is cost-prohibitive.

Principles of Microbial Weed ControlBoyetchko, 1997

Approach Classical – agent selection, inoculation, self-

perpetuating, long term protection. Inundative – mass production, application at

high inoculum levels over a localized area, short term, repeated application.

Augmentation – re-establishment of a classical agent.

Classes Mycoherbicide – fungal pathogen Bioherbicide – fungi and bacteria

Microbial Weed Control

Bruckart and Dowler, 1986: rust fungi are effective biological control agents - USDA

Templeton, 1988: predicted widespread adoption can be achieved

Strobel, 1991: predicted that bioherbicide use will realize a tremendous increase in agriculture

Why Bioherbicides? Demand for decreased use of pesticides Large areas where herbicide application not

possible or not cost effective Damage to the environment Contamination of our water supply High yield losses still occur

$619 million in vegetable, $441 million in fruit and nut crops in the US

Ideal Characteristics of a Bioherbicide

Produce abundant and durable inoculum in culture

Be target specific Be genetically stable Be capable of killing a significant

portion of the weed population under a variety of environmental conditions (weed densities)

Boyetchko, 1997

Herbicide resistant weed population Detrimental effects on non target organisms

Native plants

AGENTS USED AS BIOHERBICIDES

FUNGI BACTERIA

VIRUS

Major Characteristics of Microbial Bioherbicides

Trait Bacteria Fungi Virus

Culture Easy Easy Host

Specificity Excellent Good Excellent

Field Performance Variable Variable Unknown

Formulation Variable Excellent Unknown

Effectiveness Variable Variable Excellent

Genetic stability High Medium Unknown

Specificity of bioherbicides

Pathogens of plant (i.e. bioherbicides) are generally host specific.

Cherrington, C. A. and L. F. Elliott. 1987. Incidence of inhibitory pseudomonads in the Pacific Northwest. Plant and Soil 101:159-165. Isolated pseudomonads from downy brome,

winter barley, winter wheat, pea, lentil roots

Found 106 - 108 CFU per gram dry weight Found isolates that reduced downy brome

root growth but not wheat root growth

Kennedy, A. C., L. F. Elliott, F. L. Young and C. L. Douglas. 1991. Rhizobacteria suppressive to the weed downy brome. Soil Sci. Soc. Am. J. 55:722-727 1000 isolates, 18 inhibitory

to downy brome and not wheat Reduced DB population up to

30% Reduced DB shoot weight up

to 42% Increased winter wheat yields

35% Both in greenhouse and in

field trials in eastern Washington

COMMONLY USED MYCOHERBICIDES

Many fungi have been shown to exhibit broad spectrum weed control ranges.

TABLE 1 EXAMPLES OF FUNGAL BIOHERBICIDES FOR ECONOMICALLY IMPORTANT TERRESTIAL AND AQUATIC WEEDS

WEED PATHOGEN REFERENCE

1. Velvet leaf

Colletotrichum coccodes,Fusarium lateritium

Hodgson et al., 1988Walker, 1981

2.Wild oat Septoria tritici Madariaga and Scharen, 1985

3.Water hyacinth

Alternaria eichhorniae

Shabana, 1987

4.Sickle pod Pseudocercosporanigricans

Hofmeister and Charudattan,1987

5.Barnyard grass

Cochliobolus lunatus

Scheepens, 1987

EXAMPLES OF BROAD-SPECTRUM FUNGAL BIOHERBICIDES TESTED FOR WEED CONTROL

PATHOGEN WEED SPECIES OR FAMILY

REFERNCE

Alternaria cassiae SicklepodCoffee sennaShowy crotalaria

Boyette, 1988; Charudattan etal., 1986; Walker, 1982, 1983

Amphobotrys ricini Members of Euphorbiaceae

Holcomb et al., 1989; Whitneyand Taber, 1986

Colletotrichumgloeosporioides

Members of Leguminosae,Malvaceae, Convolvulaceae(dodders)

Daniel et al., 1973; Mortensenand Makowski, 1997

Myrotheciumverrucaria

Sicklepod; various species ofother plant families

Walker and Tilley, 1997

Bacterial Biological Control Agents

Xanthomonas campestris pv. poannua - postemergence activity on annual bluegrass in bermudagrass lawns (Johnson, 1994: Johnson, Wyse, Jones, 1996).

Pseudomonas syringae pv. tagetis - Canada thistle in soybean (Johnson, Wyse, Jones, 1996).

Risks associated with bioherbicides

In most instances the potential risks associated with the use of Bioherbicides may includes certain concerns such as:-

worker exposure and safety Plant host range effects to nontarget organisms

(competition/displacement of beneficial microbes in the community)

production of chemicals that are persistent or toxic to mammalian systems

Several examples in which bioherbicidal risk has been published is presented belowPuccinia melampodii, a rust fungus isolated in Mexico, was

approved

for release in Australia in an integrated strategy to manage

the highly allergenic weed, Parthenium hysterophorus, even though

it could also sporulate on several marigold and sunflower cultivars

(Evans, 2000). The Australian Quarantine and Plant Inspection

Service concluded that the actual and potential hazards involved

in not attempting to control this weed were significantly greater

than the perceived risks to nontarget plants.

One of the major hurdles in the use of bioherbicides is the risk associates with that of secreted metabolites.

Fungi secrete a wide range of metabolites, some of which are important medicines or research tools (Vey et al., 2001). Some of these metabolites are highly toxic (fumonisins, ochratoxins, patulin, zearalenone) or carcinogenic (moniliformin, aflatoxin). A large amount of data has accumulated on mycotoxin contamination of foodstuffs and the risk these metabolites (mostly from saprophytic fungi) pose to human and animal health (Abramson, 1998). In contrast less is known about metabolites from fungal biocontrol agents, particularly those from commercialized mycoherbicides, mycoinsecticides, and mycoparasiticides (Strasser et al., 2000; Vey et al., 2001).

RECENT ADVANCES IN BIOHERBICIDES DEVELOPMENT

There are two particular areas where there appears to be cause for optimism in the mycoherbicides field; the use of virulent pathogens for the treatment of the cut stumps of weedy trees in forest ecosystems, and weed control targeted at the leisure industry (Evans et al., 2001). A recent example of the former concerns using the silver leaf fungus, Chondrostereum purpureum, for control of black cherry (Prunus serotina: Rosaceae); an invasive North American species which is a serious threat to conifer plantations, as well as to native woodlands in the Netherlands (De Jong et al., 1990)

The bioherbicide, Biochons, is currently being marketed by Koppert Biological systems as an environmentally friendly solution to undesirable tree regrowth. The use of this pathogen for management of weedy, endemic, deciduous trees in conifer plantations and amenity areas is also being evaluated in Canada(Prasad,1994).

In complete contrast, advanced technology and largecompanies are currently involved in the development ofbioherbicides in Japan, not only in crop protection butalso in the highly lucrative leisure industry. The mosttroublesome weed in golf courses is annual bluegrass(Poa annua) and chemical herbicides are either

nonselectiveor now considered to be environmentallyundesirable. A highly specific, bacterial endophyte,Xanthomonas campestris pv. poae, has recently (1997)been registered under the name Campericos, andconstitutes the first bacterial herbicide to reach thecommercial market (Imaizumi and Fujimori, 1998).

There is no doubt that formulation has played a key

role in the marketing of bioherbicides, such as Campericos, in order to overcome problems with storage,establishment and efficacy in the field. Essentially formulation is mixing the active ingredient, in this casethe biological propagule, with a carrier or solvent andother adjuvants in order to develop a product which can be stored, for at least 1 year, effectively applied to the target weed with safe and consistent results.

FUTURE OF BIOHERBICIDES

The development of bioherbicides are less expensive than for chemical herbicides (Templeton et al., 1986). For example, the cost of developing COLLEGO was approximately $1.5 million in research and development in the late 1970s and early 1980s (Heiny and Templeton, 1993), and the cost of developing BIOMAL was estimated to be about $2.6 million(J.R. Cross, Philom Bios, personal communication).These development costs, compared to the $30 millionore more to discover and develop a chemical herbicide, make bioherbicide development quite favourable (Heiny and Templeton, 1993).

The role of biomicrobial herbicides in agriculture, however, is still problematic and insignificant. Nevertheless, because of pressures to reduce the reliance on chemical herbicides, bioherbicides could make a significant contribution to weed control. In the future, once the well-documented constraints have been overcome, particularly through improved target selection, formulation and marketing.

BAYOT,R., A.K.WATSON, AND K.MOODY, 1992.

Prospects for the development and utilization of bioherbicide technology for major

rice weeds are very good. Work in this area is preliminary for the most part, but

virulent pathogens of some potential weed targets have been identified and initial

laboratory and field results are encouraging. Increased activity in basic and

applied science and in biotechnology have a definite role to play in development,

implementation, and advancement of this weed control strategy in tropical and

subtropical regions. Virulence, efficacy, fermentation, formulation, and application

are aspects of prime importance. Industry must become more involved in small

niche markets, and techniques must be developed for subsistence farmers as well

as modern ones. There is likely to be increased pressure from public and

governmental bodies to reduce the use of chemical herbicides. We are challenged

to find acceptable, effective complementary weed control tactics.

REFERENCES

Advances in bioherbicides development—an overview: R. Mohan Babu, , A. Sajeenaa, K. Seetharamana, P. Vidhyasekarana, P. Rangasamy, M. Som Prakash, A. Senthil Raja, K.R. Biji

BIOHERBICIDES: RESEARCH AND RISKS- ROBERT E. HOAGLAND, C. DOUGLAS BOYETTE, and MARK A. WEAVER

Southern Weed Science Research Unit, USDA-ARS, Stoneville, Mississippi, USA

HAMED K. ABBAS Crop Genetics and Production Research Unit, USDA-ARS,Stoneville, Mississippi, USA.

•CURRENT STATUS OF BIOHERBICIDE DEVELOPMENT AND PROSPECTS FOR RICE IN ASIA - Alan K. Watson.Plant Science Department, McGill University, 21,111 Lakeshore Road,Canada.•Boyetchko, S. M. 1997. Principles of biological weed control with microorganisms. HortSci. 32(2):201- 205.•Cherrington, C. A. and L. F. Elliott. 1987. Incidence of inhibitory pseudomonads in the Pacific Northwest. Plant and Soil 101:159-165.

Kennedy, A. C., L. F. Elliott, F. L. Young and C. L. Douglas. 1991. Rhizobacteria suppressive to the weed downy brome. Soil Sci. Soc. Am. J. 55:722-727

Heiny, D.K., Templeton, G.E., 1993. Economic comparisons of mycoherbicides to conventional herbicides. In: Altman, J. (Ed.),Pesticide Interactions in Crop Production. CRC Press, Boca Raton, FL, pp. 395–408.

Bayot, R., A.K. Watson, and K. Moody.1992. Control of paddy and aquatic weeds

by pathogeninPhilippinesIn: IntegratedManagement of Paddy and Aquatic Weeds and Prospects for Biological Control. Food and Fertilizer Technology Center, Taipei, Taiwan.