INSECT PESTS, DISEASES, WEEDS - PREVENTION AND CONTROL
Insect Pests: Insect pests can be divided in to 3 main groups:
1. Chewing insects
2. Sucking insects
3. Boring, mining & soil insects
INSECTICIDES
Insecticides can be divided in 3 types depending upon their mode of action on the insects.
Contact insecticides: Contact insectides are capable of killing an insect, which merely comes in contact with a plant on which a contact insecticide has been sprayed. Contact insecticides give a superficial layer of protective coating on surface of plants. In heavy rains, this coating is washed off; hence in monsoon they are not very effective. Certain part of a plant, which has not been treated, could harbour some insects without harm. But contact insecticides have certain advantages too. They are quicker to act. They are capable of killing an insect, which merely comes in contact with a plant treated.
There are some insects, which bore through the parts of plants or cover their bodies with protective webs or waxes. These can not be killed by contact insecticides. To kill such insects, systemic insecticides are very useful.
Systemic insecticides: Systemic insecticides once absorbed by the plant circulate through all parts of plant. Thus, even the insects eating the roots would get killed, when only upper parts of the plant are sprayed. As the plant absorbs these insecticides, they do not wash off even in heavy rains. Since leaf pores are located on underside, while spraying of systemic insecticides, care has to be taken to see that the spraying is done mainly on the underside of the leaves. In case there is no spray pump, systemic insecticides could be applied near the roots also. One drawback of systemic insecticides is that they will not kill the insect, unless the insect chews a part of a plant or sucks the sap of the plant.
Fumigant insecticides give off fumes, which are capable of killing insects.
CHEWING INSECTS
Grasshoppers: Camouflage easily on plants due to their green or brownish colours. These insects cut irregular cuts and punctures on leaves. Tender shoots too are eaten. Their droppings are like tiny pieces of charcoal. As they hop from plant to plant, grasshoppers may be or may not be present on the damaged plant.
Brown tussock caterpillar: It is a larva of a moth which lays its white eggs in clusters, usually on the underside of leaves. The tiny, hairy caterpillars in a flock start scraping leaves. This makes the affected leaves look translucent. As they grow, they start nibbling the leaves, which get cut irregularly. Tender shoots, flower buds too are affected. Droppings of the caterpillars are globular.
Chafer beetle: This beetle too causes irregular cuts and punctures on leaves. This insect is active in rainy season. The chafer beetle is a nocturnal creature and causes the damage only at nighttime. During the day they hide in the soil.
Lemon Butterfly Caterpillar: This common and beautiful butterfly lays its solitary eggs on leaves of citrus plants. The tiny caterpillars, which hatch out of the eggs, resemble droppings of sparrows in colour and shape. Leaves and new growth is all chewed up. As the caterpillar grows bigger, it acquires green colour and then easily camouflages amongst the foliage.
Leaf Tier Caterpillar: This pale green caterpillar with black head is a larva of a moth. Plants of ginger family are targeted by this caterpillar. As the name implies, this caterpillar rolls and ties a leaf edge with silky secretion. Under the rolled edge, the caterpillar hides and eats leaves.
Semi Looper: These wire thin caterpillars are experts in camouflaging. They are always of the same colour of the plant on which they feed. Apart from the colour of their body, when they detect some trouble, they stand erect on their hind lags; and as a result look very much like a leaf stalk. Unlike other caterpillars, a semi looper walks by forming a loop between its extremes and then stretching.
SUCKING INSECTS
Aphids: These winged or wingless, tiny insects flock in great numbers on tender shoots and flower buds and suck the sap. They flock and breed in such profusion that they cover the entire stems and flower buds. They are more common in winters. Aphids attack most cultivated plants. Apart from causing the damage by sucking the sap, they are also capable of infecting the plants with viral, bacterial and fungal diseases.
Scales: Brownish irregular scaly growths on branches of hibiscus plants are actually colonies of brown scale insects. These are soft bodied insects with brown or blackish colour, having spine-like outgrowth on their bodies. Hard scales, resembling mini shields, cover entire stems of rose plants. All scale insects are capable of movement in their juvenile stage only. The hard scales insects, as they settle on plants to suck the sap, start secreting a waxy substance. This Wax covers their bodies entirely, thus making them immobile and impregnable from contact type of insecticides.
Mealy Bugs: This common wooly and white insect attacks most plants in a garden. Due to their fungus-like appearance and immobility, many people confuse them with fungus. However, below the wooly growth, they have extremely soft, pink bodies. Like aphids and scales, they too flock in great number on plants. These insects attack all parts of a plant, even the roots.
Trhips: The thrips are so tiny that they can not be seen easily. They are winged and are capable of flight. Thrips cause immense damage to tender shoots and flower buds. Thrips have saw-like mouth parts with which they rasp the parts of plant and suck the juice. The affected parts look as if they are burnt. These insect are more common in hot summer days. As the damage caused by them resembles sunburns, people unaware of the presence of these insects, normally confuse the damage to be of sunburn.
Jassids: They are also known as leaf hoppers. These tiny, winged insects are common in monsoon. Very often, attracted by lights, they come in houses at night. They are about the size of a wheat grain and the colours vary from green to brown.
Red Mites: Mites are not insects. Mites are tiny spiders, red or brown in colour. They attack most plants. Their presence is indicated by dusty formations on the affected leaves. This is due to the dust, which settles on the webs spun by these tiny creatures. The affected leaves also show numerous colourless spots. This is due to constant sucking of plant juices.
Leaf-Cutting Bee: This is a type of a bee and is comparatively harmless. This bee cuts neat, circular or oval pieces of leaves only along the leaf edge. The pieces so cut are rolled to form a nest to lay the eggs. The leaf-cutting bee does not chew plant parts, neither does it suck sap.
BORING, MINING & SOIL INSECTS
Citrus Leaf Miner: This minute caterpillar mines irregular shaped and glistening galleries in citrus leaves. Due to its habit of hiding inside the leaf, it is impervious to contact insecticides.
Ixora Caterpillar: These tiny brown caterpillars attack new shoots of Ixora and also the buds and flowers. The caterpillar bores through buds and as it eats, it secretes a waterproof web around the affected area. The webs are full of the caterpillar's droppings.
Digger Wasp: Tunnels on pruned stems of a rose plant are made by these tiny wasps. The tunneled stem dries and dies. This tunnel could harbour fungal or bacterial infection like die back or canker disease.
Gall causing Caterpillars: The swollen outgrowths on a stem of Bhendi or Tondli creeper are caused by a tiny caterpillar. The affected stems get deformed and then wither and die.
Bark Eating Caterpillar: Unlike other caterpillars, this attacks only the matured, woody trees. The caterpillar starts eating the bark first but gradually bores through the wood and travels upwards in the branch. The bored branch ultimately dies. Continued infestation can kill a giant tree.
Ants: Ants are capable of damaging the seeds. Sometimes they carry off the seeds sown. Due to their tunneling in ground, they are capable of disturbing roots of saplings, but otherwise they do not harm plants directly. Some sucking insects like aphids and mealy bugs secrete sugary drops. These sugary drops attract the ants. Ants help the sucking insects by carrying their (sucking insects') young ones to new sites. As the branch dries due to constant sapping of juices, the sucking insects, which are almost immobile, perish along with the branch. This would deprive the ants of their favourite food. Thus the ant helps the insects in return for the sugary drops.
White Grubs: These are larvae of beetles. Both larvae and the beetle are pests. Grubs gnaw at roots and the beetles chew the greens. Adult beetles lay their eggs in decaying matter. Their infection starts normally through farmyard manure or compost pits.
Snails and slugs: These pests affect only the damp areas in a garden. Mostly they shelter in the soil in the day time and feed on plants by night. They leave a sticky glistening trail as they crawl. Snails have shells on their backs and slugs have no shells. They are bisexual creatures and can reproduce even without mating. In dry spells they go in to hibernation and wake up when seasons are favourable.
Millipedes: Millipedes normally eat decomposed matter in soil. However, if starved of food, they may devour roots.
Pill Bugs: Pill bugs are soft bodied insects, which look like tiny cockroaches. They feed on tender hair roots. When disturbed, they roll in to a ball shape; hence the name pill bugs.
INSECT FRIENDS 
All insects are not pests. One should know the insects, which are beneficial to mankind. Dragonflies, damselflies, praying mantis, lacewings and lady beetles feed on other insect pests. Bees help in pollinating flowers, upon which fruiting and seed formation depends. Using insecticides indiscriminately can cause harm to the beneficial insects too.
PLANT DIEASES
Plant diseases are either non-infectious or infectious. Non-infectious diseases are caused by very low temperatures, mineral excesses and deficiencies. Infectious diseases are caused by parasitic organisms like fungi, bacteria or virus pathogen. Diseases caused by fungi are easier to control than the bacterial and viral diseases.
Fungal Diseases: Rust, black spots, powdery mildew, seedling damping off, Coconut crown rot are some of the fungus diseases.
Rust: Plants affected with rust, get rust coloured patches on leaves and other parts.
Black spots: In winter and in monsoon, dewdrops or raindrops remaining on foliage encourage this fungus disease. Small brownish-black spots appear on the leaves, which get enlarged with yellow margins. The affected leaves turn complete yellow with black spots and the fall down.
Powdery Mildew: This disease too infests plants in monsoon or in winter. Affected parts get white powdery patches. The patches gradually turn yellowish. The affected leaves fall down. Spores of this fungus are airborne and thus spread easily. In downy mildew the fungus growth is hairy.
Seedling Damping Off: Over-watered seedlings rot near soil surface and collapse. This disease can be prevented but the seedlings affected can not be saved.
Coconut Crown Rot: This fungus disease is caused mainly because of rhinoceros beetle, which chews and bores through a crown of a coconut palm. The fungal infection spreads through the wounds created by this beetle. Once the crown rots, it is impossible to save a coconut palm. By controlling rhinoceros beetles this disease can be prevented to quite some extent.
Bacterial Diseases: Canker disease is caused by bacterial infection. The affected parts form corky outgrowth. Stems tend to crack open. Rose plants and citrus plants are quite susceptible to this disease. In lemon plants leaves, stems and even the fruits get the smallpox-like corky outgrowth.
Viral Diseases: Most viral diseases are incurable. Seasonal plants and short life plants like Banana and Papaya affected with viral diseases need to be destroyed. Aphids are vectors of many viral diseases. By controlling aphids, viral diseases can be prevented to some extent. Bunchy top of Banana, leaf curl of Tomato and brinjal, Chili and Papaya, yellow mosaic leaf of Bhendi are some of the virus diseases.
Weeds: Any plant growing in an unwanted place is a weed. Amongst the weeds, grasses are more difficult to kill. Leaves produce food for plants. Constant removal of leaves can starve a plant to death. So by regular removal of above-ground parts can kill a weed. Covering weeds with black polythene sheet also can kill them. The plants thus covered do not get sunlight for photosynthesis. The extreme heat generated under the black polythene sheet can also kill many weeds. The polythene sheet also prevents new weeds from sprouting. Weedicides are of three types. General Weedicides will kill all weeds which come in contact with it. The broadleaf weedicides will kill all plants except grasses. Grass weedicides will kill only grasses but not the broadleaf plants. All weeds must be exterminated before they form seeds; else seeds dispersal will make eradication impossible.
|
PESTICIDES CHART | |||
|
Scientific name of pesticide |
Trade name of pesticide |
Original strength of the pesticide |
Desired dilution for spraying |
|
Endosulphan |
@ Thiodon |
35 percent |
0.07 percent |
|
Carbaryl |
$ Sevin |
50 percent |
0.10 percent |
|
Dimethoate |
@ Rogor or Dimethos |
30 percent |
0.05 percent |
|
Dicofol |
@ Kelthane |
18.5 percent |
0.25 percent |
|
Dinocap |
@ Karathane |
25 percent |
0.05 percent |
|
Diclorvos |
@ Nuvan |
76 percent |
0.10 percent |
|
Monocrotophos |
@ Nuvacron |
40 percent |
0.05 percent |
|
Malathion |
@ Cythion or Sumithion |
50 percent |
0.10 percent |
FUNGICIDES
|
Scientific name of pesticide |
Trade name of pesticide |
Original strength of the pesticide |
Desired dilution for spraying |
|
Carbendazim |
$Bavistin |
50 percent |
0.10 percent |
|
Captafol |
$ Difolatan |
80 percent |
0.30 percent |
|
Sulfer |
$ Wetsulf or Sulfex |
70 percent |
0.30 percent |
|
Zineb |
$ Dithane Z-78 |
80 percent |
0.20 percent |
|
Benlet |
$ Benomil |
50 percent |
0.10 percent |
WEEDICIDES
|
Scientific name of pesticide |
Trade name of pesticide |
Original strength of the pesticide |
Desired dilution for spraying |
|
Glyphosate |
@ Glycel 41% SL |
41 percent |
|
|
Paraquat Dichloide |
@Gramoxone |
24 percent |
|
NOTES: @ Liquid, $ Powder
To estimate the quantity of the pesticide for desired dilution for spraying, following formula is to be used:
Quantity of the solution needed in liters x Desired dilution for spraying ÷Original strength of the pesticide = Quantity of the pesticide needed.
Example: If 50 liters solution of water & Rogor is to be sprayed on plants then what quantity of Rogor will be needed?
Rogor is 30 percent dimethoate & its desired dilution should be 0.05 percent - 50 x 0.05 ÷30 = 0.083 liters = 83 milliliters
In 50 liters of water, if 83 milliliters of Rogor is mixed, then it will be desired solution of 0.05 percent
Example: If 10 liters solution of water & Bavistin is to be sprayed on plants then what quantity of Bavistin will be needed?
Bavistin is 50 percent Carbendazim & its desired dilution should be 0.10 percent - 10 x 0.10 ÷50 = 0.02 kilogram = 20 grams
In 10 liters of water, if 20 grams of Baivistin is mixed, then it will be desired solution of 0.10 percent.