Agriculture for Engineers 4 (3+1)

Lesson 27. Introduction to weeds

Losses caused by weeds to the society:

1. They reduce crop yields by competiting with crop plants for nutrients, moisture, solar radiation and space.

2. Their presence in field or mixture with crop,  deteorate the crop quality.

3. When eaten they harm animal health due to high content of tannins, oxalates, glucosides or nitrates.

4. They harm human health e.g. Argemone mexicana causes dropsy.

5. In aquatic ecosystem they transpire lot of water, their presence interfere fishing, hinder navigation, water flow in canal is slowed down and potable water bodies are fouled.

6. Presence of dried weeds in industrial area may cause fire hazard.

7. Their presence in forest reduces the native species.

8. They mar the asthetic value of a place.

 27.2 Weed Prevention

Weed prevention comprises all measures which deny the entry and establishment of new weeds in an area. It also includes farm hygiene that prevents the every year production of seeds, tubers, and rhizomes of the weed species already present on the farm.

 Some major aspects of weed prevention on farmland are as follows:

27.2.1 Use Weed free crop seeds

One important way the weeds spread on the farmlands is through crop seeds, contaminated with the weed seeds. Some weed seeds always go with certain crop seeds, for example, Avena fatua and Brassica spp. with small grains.

The prevention of weeds that disperse with the crop seeds can be achieved in two ways,

(I) By the production of weed free crop seeds at the Government farms or at the farmer’s field itself, and

(II) By cleaning the crop seeds of weeds before storage as well as at the time of sowing.

27.2.2 Avoid contamination of manure pits

It is a common practice of adding mature or even blooming weeds and their vegetative propagules to manure pits in the hope of recovering their manurial value. In most cases the weed seeds do not lose their viability in the manure pits and the resulting farm-yard manure serves as a notorious source of adding weed seeds to crop land.

27.2.3 Prevent Contamination of manure pits

Do not permit livestock to move from the weed-infested areas directly into clean areas because they can always drop weed seeds and fruits attached to them or those ingested by them earlier. The farm machinery, for similar reason, should be cleaned properly before moving it from one field to another. Same is true of the movement of nursery stock, gravel, sand, and soil from weed-infested areas to the new ones.

27.2.4 Keep non-crop areas clean

The irrigation and drainage ditchers, fence lines, farm boundaries, bunds, and other like un-cropped areas are often neglected by farmers. These places offer a perpetual weed nursery for the cropped plots. This should be prevented by extending the weed control efforts to non-crop areas on the farm.

27.2.5 Keep vigilance

A farmer should inspect his farm areas periodically for some strange looking weed seedlings. The search for them should be extended into standing crops even if herbicides or cultivators were used to control weeds there. No sooner than any strange looking weed seedling are noticed, they should be uprooted by digging as deep as their roots may have penetrated the soil, and the soil in these spots should be treated with a suitable sterilant.

27.2.6 Legal measures

Legal measures are necessary to check inter-state and inter-country movement of noxious weeds if the cost of having to control additional alien weeds is to be saved. Unfortunately, thus far, in most parts of the tropical and sub-tropical word, noxious weeds have not been subjected to strict quarantine laws. This has resulted in the introduction and spread of some of the costliest weeds of the world.