Insect Pests of Fruits, Plantation, Medicinal & Aromatic Crops

Plant protection appliances

• The important methods of applying pesticides are dusting and spraying. The dusting operation allows the dust particles when falling free either slowly to settle down due to gravity or drift for long distance due to wind. The appliances that are used for applying dust formulations of pesticides are called dusters. They are either manual or power operated.
• The spray fluid may be solution, an emulsion, or a suspension toxicant. To achieve an effective control of pest, the toxicant is well distributed and to meet this requirement the spray fluid is blown down to fine droplets. The spraying machines may be either hand operated or power operated ones. Commonly employed manual operated sprayers are (i) knap- sack sprayer (hydraulic or pneumatic), sprayer and pneumatic hand sprayer. Rocker sprayers are useful for tall trees and pneumatic hand sprayers are helpful to spray in gardens. The power operated mist blowers are useful in field cover more area in a limited time. A spray volume of 150 to 200 water is necessary to one hectare of land with power spray with low pressure high volume sprayers but with low press volume sprayers like knapsack sprayers require about 450-500 water to cover one hectare. Insecticides should be applied in the morning or evening hours when the weather is calm or else they will fall on unwanted areas and also may not hit the target. Before application insecticides, it must be ensured that there are no pollinators (like-bees) in the area; for the same reason insecticides should not be applied during blossoms when bees are likely to be at work. After application of insecticides a time lag (7 – 10 days in case of organophosphorus compounds and 20-30 days in case of organochlorine compounds) should be given before consuming the produce. During this period, the insecticides will get degraded and become non-toxic.
Non-insect pests

• Besides the different kinds of insects which damage crops, mites, rats, birds and nematodes cause damage to crop plants.
A. Mites

• Mites possess four pairs of legs as against insects which do have only three pairs of legs. In recent years the mites have become major pests. They cause damage by way of sucking the cellular materials by forming severe deformities. The, chemicals which are used to control the mites are known as 'acaricides'. Sulphur, ethion, dicofol, phosalone are commonly used as acaricides at the rate of 15ml per 10 litres of water.
B. Plant nematodes

• Plant nematodes are small organisms which live soil around the roots of plants. They are about 0.1 to 1.00 mm in length. They are confined to the top 20 to 25 cm of soil, sometimes even to a depth of 3 to.4 m. They are spread from one field to another through percolating water and agronomic practices like ploughing and weeding which involve transport of soil. Most of the symptoms of damage by plant parasitic nematodes are non-specific and often likely be confused with those caused by other pathogens or soil factors like poor drainage, lack of soil nutrition etc. Some of the commonly observed symptoms are:
1. Stunting and wilting
2. Leaf curl
3. Browning or bronzing of leaves
4. Distortion of leaves, stems
5. Brown lesions in roots
6. Knot-like galling of roots
• Control of plant parasitic nematodes is difficult, but nevertheless, necessary for obtaining profitable yields. Crop rotation with a non-host crop or application of large quantities of green leaves or grasses as mulches or summer fallowing and use of resistant varieties will reduce the incidence to some extent. Commonly used nematicides are DD mixture, dibromoethane, dibromo chloropropane, thionazin and aldicarb. In Tamil Nadu, nematode infection is a devastating problem in banana, citrus, potato and in vegetable crops like tomato, chillies and brinjal.