Methods Of Weed And Pest Control JSS1 Agricultural Science Lesson Note

WEEDS

A weed is a plant that grows in a place where it is not wanted e.g. a vegetable plant growing on a cassava plot is a weed.

CHARACTERISTICS OF WEEDS

1.                 HIGH PRODUCTIVE CAPACITY: Weeds possess high productive capacity and are always the first to emerge and grow when necessary conditions are provided.  They have many seeds.  For example, a single grass head may produce thousands of seeds.
2.                 HIGH RESISTANCE CAPACITY:  They are capable of withstanding adverse conditions because of their tough protective seed coats e.g. seeds of some legume
3.                 ABILITY TO REGENERATE:  Some weeds are capable of regenerating and therefore very difficult to eradicate commelina species, elephant grass and spear grass are examples of weeds that possess these characteristics
4.                 EARLY DISPERSED:  Weed seeds possess various devices for dispersal.  These include spines, hooks, parachutes of hair, and wind with which they are easily dispersed e.g. tridax, goat weed, and desmodium.
5.                 HIGH COMPETITIVE AND AGGRESSIVE GROWTH HABIT: Weeds possess highly competitive growth habits and can easily smother crops for example spear grass, and elephant grass can easily overrun a farm if not regularly checked.

USES OF WEEDS

1.                 FOOD:  Some weeds are used as food for man e.g. African spinach (Amaranthus coudatus) cochurs olitoris e.t.c
2.                 ANIMAL FEEDS:  Some weeds are used as food for feeding farm animals e.g. guinea grass, sedge, and elephant grass
3.                 MEDICINE:  Most weeds are medicine.  Drugs can be extracted from such weeds e.g. lemon grass.
4.                 EROSION CONTROL:  Weeds are used to control tiny erosion e.g. Bahama grass.
5.                 SOURCE OF ORNAMENTAL:  Weeds are the major source of ornamental crops e.g. e.g. pride of Barbados, caron lily, rose, croton, and hibiscus.

CLASSIFICATION OF WEEDS BASED ON LIFE CYCLE

Weeds are grouped into three classes.  These include

(i)  Annual weed  (ii)  Biennial weed  (iii)  Perennial Weed

ANNUAL WEED

These are weeds that complete their life cycle in one year.  They grow, reach maturity, and die within a year.  Annual weeds include the tridax plant, goat weed, spigelia, and so on.

BIENNIAL WEEDS

These are weeds that complete their life cycle in two years.  The first year is used by the crops to grow and store food.  Reproduction and maturity take place in the second year.  Examples of biennial weeds are wild carrots and yellow rockets.

PERENNIAL WEEDS

These are weeds that take more than two years to complete their lifecycle or are ripe for harvesting perennial weeds including giant star grass, guinea grass, carpet grass, centos, and tropical kudzu.

COMMON WEEDS

COMMON NAME                         BOTANICAL NAME

1.                     Spear grass                                    Imperata Cylindrica
2.                     Guinea grass                                  Panicum maximum
3.                     Elephant grass                               Pennisetum prupuren
4.                     Wild hemp                                     sida spp
5.                     Water leaf                                      Talinum triangulare
6.                     Goat weed                                     Ageratum consoles
7.                     Stubborn grass                               Elaisina indica
8.                     P. W. D. Weed                              Tridax
9.                     Pig weed                                        Boerhavia
10.                 Carpet grass                                   Axonopus compressus
11.                 Pigeon pea                                     Cajanus caja
12.                 Sensitive plant                               Mimosu pudica
13.                 Witch weed                                   Striga senegalenis
    

PESTS

Pest is defined as only living organisms, plants, or animals that can cause damage to our cultivated crop plants, farm animals, and humans.  Examples of common pests include insects like grasshoppers and beetles, mammals such as rats and monkeys, and birds such as weaver birds. 

CLASSIFICATION OF INSECT PESTS ACCORDING TO THEIR FEEDING HABIT

According to their mode of feeding insect pests are classified into three groups.  These are:

1.                       Biting and chewing insect pests
2.                       Piercing and sucking insect pests
3.                Boring insect pests

BITTING AND CHEWING INSECT PESTS

Insect pests in this group have mouth parts which are specially made for biting and chewing plat.  The mouth parts of insects in this group consist of a pair of very hard-biting jaws called mandibles, a second pair of the jaw called maxillae, a flat upper lip called the labrum, and a lower lip is known as librum.  The mandibles are used to bite off and chew parts of the crop while maxillae are used to bite off and chew parts of the crops into the mouth.  Examples of biting and sucking insect pests are crickets, grasshoppers, beetle, termites, armyworm, and mantels.

 PIERCING AND SUCKING INSECT PESTS

The insects in this group have mouth parts that are shaped like injection needles, called probaxix, and hena. Their mouth parts are adapted to pierce into plant parts and suck the sap and juice of plants.  Examples of piercing and sucking insects include aphids, cotton stainers, mealy buds, white flies, and capsids.

 BORING INSECTS

These are insects that bore holes into plant tissues and seeds.  Boring insects are also called burrowing insects.  Examples of boring insects are beans beetles, weevils such as rice, and maize weevil.

 CLASSIFICATION OF INSECT-BASED ON THEIR LOCATION

Based on location, insect pests are classified into two namely:

a)                 Field insect pests

b)                 Storage insect pests 

a)                 FIELD INSECT PEST:  These are insects that attack crop plants on the field that is before harvesting important field pests include:

1.     Stem borers
2.     Fruit and seeders:  Examples are beetle fruit, flies, and fruit piercing mouth.
3.  Root feeders:  Examples are yam beetles.

 STORAGE INSECT PESTS:  This group of insect attack harvested products in store.  Examples include bean beetles and weevils such as rice and maize weevils.