Biological Weed Control
Natural or biological weed control agents are those of biological origin, which suppress or kill the weeds without significantly affecting the desirable plants. They include insects, animals, fish (like Chinese carp), snails, birds (like duck), microbes (fungi, bacteria, viruses, nematodes, etc.), their toxic products, and plants (parasite plants, competing plants) or their products.
Bio-herbicide Anything of biological origin used to suppress or kill the weeds. But in modern literature the term bio-herbicide refers to microbial plant pathogens, which are applied to kill or suppress the growth of weeds. The fields of biotechnology and genetic engineering offer great scope for development of bio-herbicides as well as resistant crop plants to selected herbicide. Problems include the difficulty of commerically producing and formulating the organism while maintaining its viability .
- Fish Some herbivorous fish in rice fields eat many of the weeds. The fish found useful in this purpose are Puntius javanicus in Asia, Tilapia rendalli and T. zilli in Africa.
-Algivorous (microphytophagous) fish can be successfully used in the control of weeds and algae in the rice fields. and T. mossambica in Asia,.
-Grass carp was known to attack 21 different species of weeds in 16 families, which includes Echinochloa crusgalli, Eleocharis yokoscensis, Cyperus difformis, Rotala indica, Sagittaria pygmaea, Monochria vaginalis, and Marsilea quadrifolia.
-Tadpole shrimp (Triopus longicaudatus; T. granaris and T.cancriformis) can be used for the control of young weed seedlings in transplanted rice.
- Animals like pigs feed on the tubers of purple nutsedge (C.rotundus) in the off-season, in India.
- In control of Ludwigia parviflora in rice fields, steel blue beetle (Haltica cyaamea)
-Larvae of Bactra verutana were found to bore into shoots of Cyperus .rotundus.
Larvae of the moth Epilemma strenuata cause significant damage to the buds of Parthenium hysterophorus.
- Nematodes Rice root nematode Hirschmanniella spinicaudata indicated that many of the rice weeds - Commelina diffusa, Murdannia nudiflora, E.colona, C.dactylon, R.exaltata; C.rotundus, C.iria and C.difformis. Ageratum conyzoides and Alternathera sessilis, were found to be susceptible to above pest.
- Plant pathogen Colletotrichum gloeosporioides sp. Aeschynomene was found effective for control of Aeschynomene virginica .
-Colletotrichum gloeosporioides sp. Jussiaceae for the control of Ludwigia decurrens .
-Drechslera monoceras for the control of Echinochloa crusgalli ,
-Epicoccosorus nematosporus for the control of Echinochloa kuroguwa.
-Scirpus planculmis by a pathogen Alternaria sp.
-The rust fungus Puccinia canalicuta , was found to control Cyperus esculentus ,
-Cercospora rodamanii was found to be effective against aquatic weed Eichhornia cressipes.
- Plant bio organisms The ability of a thick azolla mat effective in suppressing to suppres nearly 75% of weed species has been found in transplanted rice.
With good water management, Azolla and Lemna minor L. can be grown to suppress weeds such as M. vaginalis, Sphenoclea zeylanica and C .difformis in wet-seeded rice.
- Plants are known to release chemicals into the environment by several means which, depending upon edaphic and climatic factors, may influence the growth of neighbouring species.
- This phenomenon could be exploited for the development of eco-friendly (nonchemical) weed management through the use of (i) allelopathic cover crops, (ii) allelochemicals as natural herbicides, (iii) allelopathic crops cultivars .
- From olden days, certain cultivated crops or individual plants such as buckwheat, black mustard, sunflower, black walnut, cereal crops such as sorghum, wheat barley, oats and rye have been widely reported to suppress weed species.