Controlling eggplant pests

Housewives normally do not buy eggplant fruits with holes in them, as these have a worm or larvae of the fruit and shoot borer inside. However, researchers of PhilRice [Philippine Rice Research Institute] have found a way of producing more eggplant fruits without any worm in them without so many insecticides spraying.

In a three-year study by PhilRice researchers, it was observed that weekly removal of damaged eggplant fruits and shoots resulted in a net incremental benefit of 128,000 a hectare. On the other hand, the net incremental benefit was reduced to only 60,000 a hectare if removal was done every two weeks.

Dong Arida, PhilRice supervising science research specialist, said the fruit and shoot borer is the most important insect pest of eggplant in South and Southeast Asia. Its larvae can be observed in the field as early as three weeks after transplanting.

Newly hatched worms bore through the shoots and apical buds of the plants in search for food. This activity of the insect causes the shoots to wilt, eventually resulting in reduced fruits of the plant.

At the fruiting stage, the worms bore through the flowers and enter the fruits just below the calyx. Damaged fruits are not marketable. Their size is abnormal. These have entry and exit holes made by the borer, which often partially heal and close as the fruits grow, making the fruits look healthy from the outside.

The butterfly of the adult fruit and shoot borer is generally brown with white wings containing brown to brownish orange markings. They fly low, are active at night, and prefer to stay at the lower surface of the leaves during the daytime. When at rest, they spread their wings outward.

The female adult is generally bigger than the male. The female lays its eggs singly on the leaves and buds. Newly laid eggs are creamy white and then turn orange when about to hatch. The eggs hatch in about four days.

Filipino farmers usually spray 56 times during a cropping season to control this insect pest. The frequency of insecticide application increases as soon as the plants start to bear fruits due to the highly visible damage in the shoots and fruits.

This tremendous misuse of pesticides results in higher production costs, longer exposure to pesticides, and development of insect resistance to pesticides.

With weekly removal of damaged fruits and shoots, pesticide application is reduced from 56 times for a five-month crop to none at all. Thus, this new strategy will surely have tremendous impact on the environment.

The researchers also noted that weekly removal of damaged fruits and shoots is comparable to insecticide application every three weeks. They said that if farmers insist in using insecticides, they would do well to spray only six times in a cropping season and save themselves from the cost and danger of spraying too much insecticide. — S. Ma. Pablico