Losses caused by weeds

1. Reduction in crop yield

• A crop field is a favorable ecosystem where a large number of weed species germinate in flushes and grow profusely.
• If no imposed they compete with crop plants for space, nutrients, moisture and light.
• Such competition retards crop growth and development, resulting in yield loss.
• The yield losses in upland rice ranged between 66 to 92.8%. The average losses due to weeds in different crops were 30- 40% in soybean, maize, potatoes, vegetables, fodder and root crops and 15-20% in other cereals.

2. Loss of quality of farm produce:

• The quality of produce in weed infested plots become poor and fetches lower price.
• Contamination of crop produce with weed seeds, particularly seeds of food grains with the seeds like Datura, Vicia, Argemone etc. are often responsible for health hazards.
• Contamination may impart odd odors in the flour of grains and lower the market value of the produce.
• If the seeds of objectionable weeds are mixed with crop seeds such produce are discarded or banded for sale.

3. Loss of men’s and animal’s health:

• Many weeds of forage land and pasture may contain alkaloids, tannins, oxalates, which show poisonous effect to the animals when feeding upon them.
• Some poisonous weeds cause irritation, allergy and eczema to animals and labourers when they come in contact with them.
• Many thorny weeds may make wounds to the animals.
• Some weeds such as Centipeda minima, Datura stramonium cause wounds, headache, sneezing and vomiting also.

4. Allelopathic effect:

• Many seeds and propagules of weeds may contain allelochemicals ((derivatives of benzoic acids, cinnamic acids, phenolic acids, coumarins, hydroquinones, benzoquinones and cineoles) certain toxic substances), which rendered the antagonistic effect (impair germination and growth) to the neighboring plants. This effect is called allelopathy.
• The important weed species that show allelopathic effect on crops are Agropyron repens, Sorghum halapenge, Lantana camera, Abutilon theophrastic, Cyperus rotundus, Eupporbic maculta, Ambrosia psitostachya

5. Reduce the value of land:

• Severe infestation of perennial, pernicious and poisonous weeds reduce the value of land as they incur heavy expenditure to clear or to eradicate.

6. Harbour insect-pest, pathogens and parasites:

• Many weeds may act host and shelter for insects, pests and diseases.
• They act as alternate hostsof a number of fungi, bacteria, virus and nematodes.
• For e.g. Chenopodium, Amaranthus and Datura are the hosts of gram caterpillar. Echinochloa, panicum are the host of rice stem borer.

7. Increase the cost of cultivation
8. Increase the irrigation requirements

• Weed transpires irrigated water and thus increases the frequency and depth of irrigation water,
• which is very often expensive and difficult to obtain.

9. Impair the purity of varieties

• Cross pollination with compatible weed plants impairs the genetic purity of the crop seeds.

10. Reduce the quality and quantity of products from livestock and birds.
11. Causes nuisance and pollution in non-cropped area like rock gardens, manure pits, threshing and drying yards etc.