Bioherbicides

1. BIOHERBICIDES PRESENTED BY:VIKRANT MEHTA ROLL NO. : 301105022

2. 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 .

3. 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 .

4. 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.

5. Principles of Microbial Weed Control Boyetchko , 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

6. 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

7. 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

8. 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

9. Herbicide resistant weed population Detrimental effects on non target organisms Native plants

10. AGENTS USED AS BIOHERBICIDES FUNGI BACTERIA VIRUS

11. Major Characteristics of Microbial Bioherbicides

12. 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 10 6 - 10 8 CFU per gram dry weight Found isolates that reduced downy brome root growth but not wheat root growth

13. 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

14. COMMONLY USED MYCOHERBICIDES Many fungi have been shown to exhibit broad spectrum weed control ranges.

15. TABLE 1 Examples of Fungal Bioherbicides for Economically Important terrestial and aquatic weeds WEED PATHOGEN REFERENCE Velvet leaf Colletotrichum coccodes , Fusarium lateritium Hodgson et al., 1988 Walker, 1981 2.Wild oat Septoria tritici Madariaga and Scharen , 1985 3.Water hyacinth Alternaria eichhorniae Shabana , 1987 4.Sickle pod Pseudocercospora nigricans Hofmeister and Charudattan , 1987 5.Barnyard grass Cochliobolus lunatus Scheepens , 1987

16. Examples of broad-spectrum fungal bioherbicides tested for weed control PATHOGEN WEED SPECIES OR FAMILY REFERNCE Alternaria cassiae Sicklepod Coffee senna Showy crotalaria Boyette , 1988; Charudattan et al., 1986; Walker, 1982, 1983 Amphobotrys ricini Members of Euphorbiaceae Holcomb et al., 1989; Whitney and Taber, 1986 Colletotrichum gloeosporioides Members of Leguminosae , Malvaceae , Convolvulaceae (dodders) Daniel et al., 1973; Mortensen and Makowski , 1997 Myrothecium verrucaria Sicklepod ; various species of other plant families Walker and Tilley, 1997

17. 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).

18. 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

19. Several examples in which bioherbicidal risk has been published is presented below Puccinia 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.

20. 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).

21. 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)

22. 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).

23. In complete contrast, advanced technology and large companies are currently involved in the development of bioherbicides in Japan, not only in crop protection but also in the highly lucrative leisure industry. The most troublesome weed in golf courses is annual bluegrass ( Poa annua ) and chemical herbicides are either nonselective or now considered to be environmentally undesirable. A highly specific, bacterial endophyte , Xanthomonas campestris pv . poae , has recently (1997) been registered under the name Campericos , and constitutes the first bacterial herbicide to reach the commercial market ( Imaizumi and Fujimori, 1998).

24. There is no doubt that formulation has played a key r ole 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.

25. 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).

26. 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.

27. 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.

28. 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

29. 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.

30. 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.

31. 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.