BIOTECHNOLOGICAL APPROACHES TO WEED MANAGEMENT

Weed management is essential for good quality and quantity of food production. The presence of weeds in general may reduce crop yield by about 30% or more. Being potential pests, weeds have to be removed employing mechanical, chemical cultural and biological means. Weed management through application of chemicals (herbiciedes) is, through effective, not eco-friendly. The herbicides may pollute the environment and many alter the natural equillibrium. They also endanger and alter plant and microbial biodiversity. Effective non-chemical weed management may include various biotechnological approaches using plants and/or their products. These are useful both for the natural aquillibrium and the environment. in addition they also condition the soil and improve crop production. Some of the recently evolved biocontrol and biotechnological methods od weed management developed and tried at the National Research Centre for Weed Science, Indian Council of Agricultural Research, Jabalpur are outlined in the following text for ready use for trials and for working our their cost effectiveness.

1. Management of Phalaris minor in wheat by using fungi :

At present Phalaris minor is one of the most predominant weeds in wheat fields. The Weed spreads through seeds. The weed has developed resistance against popular herbicides like isoproturon. Biotechnological approach using fungi offers an alternative possibility of management of the weed through biocontrol.

i) Control of Phararis minor using Trichoderma viride :

Trichoderma viride is used as a seed dressing fungi in various crops including in wheat for management of seed borne/soil borne pathogens. Interestingly, the fungus has been found to inhibit germination of seeds of Phalaris minor. Application of Trichoderma, viride grown in saw dust and neem oil cake as a base consistently inhibits germination of phalaris minor seeds and reduces vigour of the seedings of the weed. At the same time it improves yield of wheat by about 5% . The fungus has potential of controlling phalaris minor. Soil application of the fungus, wheat seed treatment and spray of the fungus were all effective in controlling the weed.

ii) Control of Phalaris minor by gilocladium virens : Control of Phalaris minor by ?Gliocladium virens has also been found to have potential for control of Phalaris monor by inhibiting seed germination in a similar manner as does the Trichoderma viride.

2. Management of parthenium (Parthenium hysterophorusL) by marigold (Tagetes patulaL)

Parthenium is an obnoxious weed of worldwide occurence, harmful to human and animal health, agriculture, environment and the natural biodiversity. The weed reduces yields of crops and grasses. When shown in parthenium infested field or area, marigold inhibits seed germination and growth of the weed. It also reduces population of the weed. In the next generation, reduction of parthenium population is as hight as 85-100%. This has been found primarily due to competition and through allelopathy ( affecting parthenium plants by releasing chemical substances including thicophene into soil through roots.) Built up of the phytotoxic substances of marigold origin prevent parthenium seed germination, growth of plants, and flower and seed production completely in 2-3 years. This technology appreas to be economically rewarding for marisgold flowers have good market. This can be achieved simply by spraying marigold seeds over parthenium infested area. The technology is simple, effective, economically rewarding, and ensures self perpetuating control of parthenium in wastelands. Marigold to parthenium plant ratio of 0.5 to 4 aoppear effective for near complet control of parthenium. Adequate moisture availability in soil facilitates establishment of marigold in parthenium infected area.

3. Management of Parthenium by fungi: Two fungal species namely Gliocladium virens and Trichoderma viride which have been widely used as seed dressing to present parthogenic damage have also been found effective for parthenium control.

i) Control of parthenium by Gliocladium virus :

Glioladium vieus and 10% neem oil separately as well as in combinations spray control pathenium and other broad leaf weeds like chenopondium album, Melilotus alba and Medicago sp.

In wheat crop. The fungus could be explored as a self perp control measure for non-cropped area also.

ii) Control of parthenium by Trichoderma viride and need oil :

Thrichoderma viride and neem oil separately as well as in combinations spray control parthenium under field conditions. The fungi has potential of becoming a self perpetuating means for control of parthenium under non-cropped area. Trichoderma viride also acts as an antidote for parthogens of parthenium that can possibly be used as biocontrol agents. If any of the parthogens attack crops, the Trichoderma virid can be used to overcome the problem.

4. Management of parthenium by utilising as a source of nutrients :

Parthenium is able to extract nutrients even from nutrient deficient soils in which it grows. It has very hight levels of nitrogen (3%), phosphorus (0.2%), potassium (4.5.%) and other macro and micro-nutrients. Uprooted, dried and cut to small pieces or powdered parthenium plants at preflowering stage can be applied directly to crop fields. Apart from increasing crop growth and yields, the parthenium residue conditions soil with the organic supplement. Keeping safety considerations, it may serve as an incentive for participation of public in its ecofriengly control.

5. Weed management through mid-summer irrigation and covering the beds with black polythene :

Weed problem in most cases is due to seeds of weeds present in soil seed bank which germinate before, with or after planting the frops. Mid summer irrigation and covering the beds or fields with black polythene thoughout the summer kill most of the readily geminable seeds in soil seed bank. Polythene covering can be removed after summer before planting the crops. The treatment may provide near complete weed control. This technique is suitable for areas where summer temperature exceeds 400 c.

6 Weed management through black polythene stripe mulching Where crop is grown in rows, inter row space could be covered with black polythene mulching. This kills weeds appearing in the area due to interception of light necessary for survival of the plants.