WEEDS ENOTE

WEEK FOUR

SUBJECT: AGRIC SCIENCE

Class: GRADE 7

TOPIC: WEEDS

DEFINITION OF WEED: Weeds are plants, which are sometimes wild and they grow and compete with plant crops on a farm. In other words, weeds are plants which grow where they are not wanted i.e. they are unwanted plants. You must have seen a pawpaw tree or tomato plant growing in a maize farm. Both the pawpaw and the tomato plants are weeds in that particular farm.

ANNUAL WEEDS: There are many different types of weeds. Some are known to grow and die within one year, these are called annual weeds.

PERENNIAL WEEDS: Others which grow for many years are called perennial weeds. Many weeds have broad leaves, while some others belong to the grass family. Such weeds have long, narrow leaves. Some other weeds have underground storage parts for survival hence they are more difficult to get rid of (control). Some common weeds in a farm include ewedu, gbure (Talinum triangulare), shrubs and grasses.

Characteristics of weeds:

(a) Easily Dispersed: Weed plants usually produce many seeds. These seeds can be spread from place to place (dispersed) by man, animals, birds, wind, water, or even by explosive mechanism. In the system, the weed fruit pods burst with a loud noise and cause the seeds inside them to scatter over a wide area away from the original plant. Weed seeds which are spread by water, float for a long time on the running stream, river or even the Ocean. The seeds germinate when they are carried to land. Weed seeds which are spread by wind are usually hairy. Those with thorns or sticky hairs can get themselves attached to farmer’s clothes or to the hairs of sheep, goats or cows grazing on a farm. When the farmer removes these seeds from his clothes, he may drop them on his farm. Later, when there are favorable conditions for good plant growth, the weed seeds germinate and grow in the new place. Birds for instance eat juicy fruits such as guava. The guava seeds pass out with the faeces of the birds and germinate in a new place.

(b) Long Dormancy: Some weed seeds can remain dormant for days or even months. Such weed seeds can be those attached to the hair of animals or those carried for long distances by running water to dry land or even seeds which pass out with bird faeces. These germinate and grow in the new places where they are deposited when conditions become favorable for plant growth.

USES OF WEEDS:

(a) Medicinal Herbs: Many herbs are called weeds. Some of these herbs have medicinal properties and are used more commonly in the rural areas where access to hospitals is limited. Some of these weeds used for treating human ailments (diseases) are:

(i) Thorny Pigweed or Ahon Ekun (Acanthus montanus) for treating female hormone imbalance, menstrual cramps, arthritis, asthma, urinary disorder.

(ii) Goat Weed or Imi Esbu (Ageratum conyzoides) for treating open wounds, peptic ulcer.

(iii) Dagunro or Tete elegun (Amaranthus spinosus) for treating gout.

(iv) African Marigold or Yunriyun (Aspilia africana) for treating fresh wounds and stopping bleeding.

(v) Lemon grass or Waapa/ Ewe tea (Cymbopogon citratus) for treating malaria, rheumatism and nervous disorder.

(vi) Chickweed or Sawerepepe (Spilantbes filicaulis) for treating asthma, constipation, obesity, diabetes, impotence and tumors.

(vii) Dandelion (Taraxacum officinale) for treating low blood pressure, anaemia, water retention, diabetes, skin disease, cancer.

(vii) Mistletoe or Afomo onisana (Tapinantbus bangwensis) for treating high blood pressure, epilepsy, convulsion, stroke, hepatitis, asthma.

(ix) Sensitive Plant or Patanmo (Mimosa pudica) for treating miscarriage.

(b) Food: Many weeds are also eaten by human beings as part of their food. Some vegetables such as Tete elegun (Amarantbus spinosus), Gbure (Talinum triangulare),Yanrin etc, grow all over West Africa. They are harvested and cooked as part of our daily diet. In addition, many people brew lemon grass as tea. It serves both as a food item and a medicine especially for curing malaria fever.

EFFECTS OF WEED ON CROP

(a) Competition with Crop Plants: Weeds are disadvantageous in crop production because they compete with crop plants for water and nutrients, which they remove from the soil. Therefore, crops in a weedy farm do not grow well, hence they become stunted. This is partly because not enough water and nutrients are left in the top soil where the roots of crop plants can reach them. Since most weeds usually grow faster than planted crops, they may shade crop plants and thus prevent sunlight from getting to the crops. If such happens, the crop plants will not produce enough fruits since they cannot make enough food. Too many weeds in a farm can even cause the death of crops. If weeds are left in the farm throughout the duration of the crops, yields can be reduced by 50 to 80 per cent. The farmer who operates such a farm will surely not record a profit, hence his farm will run at a loss.

(b) Damage to Animal Skin: The fruits or seeds of some weeds have thorns. When such weeds like goat-weed for example, get themselves attached to the skin, hair or wool of animals such as goats and sheep, the weed seeds or fruits scratch the skin, thereby causing wounds or they get stuck to (tangled with) the wool. In both cases, the quality of the leather that will be produced from the damaged goat skin or the woolen cloth produced from the original wool with weed fruits or seeds will not be good and hence people who buy them will pay less money.

(c) Reduction in the Quality of Farm Products: Weeds also reduce the quantity and market value of some farm products thus reducing the profit that the farmer can make. For instance, if bitter-weeds are eaten by dairy cows while grazing, there will be an undesirable flavor added to the milk produced by the cows.

(d) Death to Animals: When cattle eat poisonous weeds, this may cause stomach upset called belching or bloat. This condition can occasionally kill the cattle, thus reducing their number and profit to the farmer.

(e) Alternate host Plant for Diseases and Pests: Weeds also act as an alternate host plant for diseases and pests. These organisms from the diseased weeds may attack crop plants thus reducing their yields. The crop plants may even die thus leading to total crop loss.

ASSIGNMENT

OBJECTIVE QUESTIONS:

1. Which of the following is NOT an agent of weed dispersal? A. Animal B. Explosive mechanism C. Temperature D. Water E. Wind

2. Any plant grown where it is not wanted is termed A. forage B. pasture C. silage D. vegetable E. weed

3. Which of the following is NOT a beneficial effect of weed? A. Addition of organic matter to the soil B. Increase in production cost C. Nutrient recycling D. Source of drugs used in public health E. Source of pesticide

4. The botanical name of goat weed is A. Ageratum conyzoides B. Aspilia Africana C. Eupatorium odoratum D. Panicum maximum E. Talinum triangulare

5. The advantage of weeds in agriculture is that they. A. are easily disperse B. have a long period of dormancy in the soil C. help in checking erosion D. produce large number of seeds E. reproduce sexually and asexually

6. The weed that is commonly use as local tea is A. lemon grass B. papaya C. panicum maximum D. talinum triangulare E. Goat weed

THEORY QUESTIONS:

1. Define weed.

2. Differentiate between annual weeds and perennial weeds.

3. List five common farm weed and where they can be found.

4. List five weeds and explain the use of one of them.

5. List five effects of weeds and explain one.