Weed Management

Weed

ØWeed is a plant growing where it is not desired.

Ø Jethro Tull a great British farmer was the first person to refer the word weed and its definition in his famous writing “Horse Hoeing Husbandry”.

Ø All weeds are unwanted plants, but all unwanted plants may not be the weeds.

Ø Weed    science  society  of  America          defined weed as a plant growing   where  it is not desired.

Ø European weed  research  society

defined weed as any plant or vegetation excluding fungi interfering with the objectives or the requirements of the people.

Ø W.S. Blatchley defined weed as a plant out of place or growing where it is not desired.

Ø W.W.Robbins et al., defined weeds as obnoxious (unpleasant) plants.

Ø  J.L.Harper defined weeds as higher plants which are a nuisance.

Classification of weeds

1. Based on morphology – Grasses, Sedges and Broad leaved weeds

2. Based on life cycle – Annuals, Biennials and Perennials

3. Based on nature of stem – Woody, Semi woody and Herbaceous weeds

4. Based on soil types – Acidophile, Basophile and Neutrophiles

5. Based on origin - Indigenous weeds and Exotic/Alien weeds

6. Based on habitat

7. Based on association

Some other terminologies

— Facultative weeds: Also called Apophytes. Weeds that grow primarily in wild community and migrated to crop fields. Eg. Opuntia dilleni

— Obligate weeds: Occur only on cultivated land. They can’t survive and withstand and

disappears when the land is not disturbed for 2-3 years. Eg. Convolvulus arvensis

— Noxious weeds: Weeds which are undesirable, trouble some & difficult to control. These weeds are also known as special problem weeds.

Eg. Cyperus rotundus. Cynadon dactylon, Circium arvense, Parthenium, Eichhornea

crassipes, Lantanacamara, Saccharum spontaneum, Imperata cylindrica and Striga spp

—  Objectionable weed: It is a noxious weed whose seed is difficult to separate from the crop seed after contamination is called objectionable weeds.

— Satellite weeds: Weeds which mature at same time and height as that of crop and have similar size and shape of their seeds as that of crop seeds are easily mixed with crop seed. Eg. Avena fatua and Phalaris minor are such weeds in winter grains. Similarly, Oryza sp. in rice, Cichorium intybus and Cuscuta sp in lucerne.

Weed dormancy

Ø Innate dormancy is a genetically controlled character. It is due to presence of  hard seed coat.

E.g. Tribulus terrestris, Ipomea sps, Xanthium sps.

Ø Enforced dormancy is due to placement of weed seeds deeper than 5cm in the soils. It is a non-specific character of the seeds and it is caused by the absence of red light.

E.g. Xantheum spp, Rumex spp

Ø Induced dormancy results from sudden physiological changes takes place in the seed.

Ø Avena fatua exhibit all the three kinds of dormancy.

 

Loss due to weed

 Weeds account for 45% loss of agriculture produce Insects – 30%

Diseases – 20%

Others (rodents) – 5%

 Weeds compete with crop plants for moisture, nutrients, space and sunlight and reduce the crop yields.

 Crop – reduction in yield due to weeds

Wheat = 15-30%

Rice = 30-35%

Maize, sorghum, pulses, oilseeds = 18-85%

Bengalgram = 30%

Redgram = 34%

Onion = 90.7%

Potato = 28%

 

 Uses of weed

Ø Weeds comprise of 2.5 times more N, 1.5 times more P, 3.5 times more K than crop plants.

Ø   Parthenium, Eichhornea crassipes, Eupatorium are used as compost and also as green manure plants. They should be used before flowering.

Ø Weeds which are used as food for human beings are Amaranthus viridis, Celosia argentia (cocks comb weed), Alternanthera sessilis, Portuluca sps, Digera sps, Chromolina odorata.

Weed	Use
Centella asiatica	Blood purifier and improves memory power
Phyllanthus niruri	Jaundice
Tylophora indica	Asthma
Solanum nigrum , Solanum xanthocarpum	Asthma, cough and fever
Argemone mexicana             oil	Skin treatment
Spirulina sps	Rich in protein
Dicanthium annulatum, Vetiveria zizanoides	Soil binders
Cynodon dactylon	Lawn
Calotrophis, Parthenium, Crotalaria	Reduces nematode population
Jatropha gossypifolia	Biofuel
Lantana camara, Opuntia dellini	Live fences