Non-chemical ways to keep apple pests away

Divender Gupta

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AMONG temperate fruits, apple is a major source of income for orchardists. It is mainly grown in Jammu & Kashmir, Himachal Pradesh and Uttarakhand. In HP, both temperate and subtropical fruit cultivation is carried out. Apple has the biggest share (over 81 per cent) in the state’s fruit production.

Pests infest the apple crop at various stages. Complete dependence on synthetic insecticides has made way for Integrated Pest Management (IPM) in recent decades. Pesticides are a major component of IPM, but their use should be need-based and stage-specific, and that too as per the recommended dosage. However, due to their excessive use, environmental and health hazards have cropped up, besides pesticide resistance. There are certain non-chemical methods which are effective in managing insect pests and can be integrated to keep insecticide use to a minimum.

Beware of borers

Root borer, stem borer and shoot borer are the main insect pests that attack the apple crop. Root borer larvae feed on roots; stem borer larvae hollow out the stem; and shoot borer larvae feed on the shoots initially and later shift to the branches and the main trunk. Root borer larvae are fleshy with strong mandibles and are about 10 cm in length when fully fed. It takes around three-and-a-half years for the larvae to reach this size. In heavy infestation, a single tree basin harbours 20-30 larvae. The symptoms appear at later stages and by that time, much of the damage has already been done. So, it is advised to collect the larvae from the tree basins by raking and destroying them at regular intervals. For stem borer management, the thrusting of a flexible wire inside holes in the stem and branches and later plugging the hole with a cotton swab soaked in petrol is quite effective; it has been observed that around 90 per cent of the active larvae are thus killed. Similarly, for shoot borer, the wire technique is useful.

The grubs of defoliating beetles feed upon the roots and cause much damage in the nursery as well as in young plantations. These grubs are C-shaped, stoutly built and have well-developed legs, which are lacking in the case of root and stem borers. Collection of the grubs by digging the basins and their destruction is a potent way to check infestation. The adults of these grubs, known as defoliating beetles, feed on the foliage in the late evenings.

The adult defoliating beetles, which are of various colours ranging from brown or dark brown to black and green and beetles of both root (chestnut brown) and stem (dark grey) borers are attracted towards light. So, if the electricity supply is available in or near the orchards, light traps should be installed to capture the beetles after dusk for 2-3 hours daily during the activity period (June-July). This will help in reducing the population of adult pests.

The woolly apple aphid is a sucking pest covered by waxy, woolly filaments due to which its infestation can be seen from a distance. It infests both aerial and subterranean parts. Its aerial population is controlled by a ‘natural enemy’, an endoparasitoid, Aphelinus mali, which parasitises these aphids. The parasitised aphids lack wool over their body. Their artificial rearing in the laboratory is not feasible so far and hence this ‘natural enemy’ needs to be conserved by using eco-friendly means of pest management. The insecticides, besides killing the woolly apple aphid, also kills the parasitoids. So in order to protect them, cut a 1-2 cm portion of the twigs having parasitised aphids and keep it away from the orchard before an insecticide spray; later, tie these twigs with the help of threads to the branches the next day so that the population of the ‘natural enemy’ does not get affected. Similarly, ladybird beetles feed on these aphids and if the population is high, try to avoid the spray or only give spot application. Also, the removal of water sprouts from the basins and covering the pruning cuts and wounds with protective paint is advocated.

The Indian gypsy moth’s larvae feed on the foliage for only three to four months (April-June/ July), but have the capacity to defoliate the tree. The damage occurs during late-evening hours when the orchardist has left the orchard for the day. During the daytime, the larvae use hiding sites such as stones and the soil. The best solution is to use traps, which are nothing but pieces of gunny bags kept in the orchards or tied loosely to the main stem. The hairy caterpillars cluster together under these pieces of gunny bags, from where these can be collected and killed. This is a very effective non-chemical way of killing the larvae. In addition, the egg clusters, which can be spotted in adjoining loose stone walls, beneath large earth clods and cracks during March-April, should be destroyed so that the caterpillars do not hatch out of them.

Burying fallen infested fruits, the use of biocontrol agents wherever feasible and pheromones, wherever applicable, are sound pest management strategies in general.

Export parameter

These methods, besides being eco-friendly, also reduce the pesticide residue in/on the fruit; this is a major quality parameter, particularly for exports. Every country has its own Maximum Residue Limit (MRL). If the pesticide residue in the commodity to be exported exceeds the prescribed limit, the consignment is not accepted. This is known as a non-tariff trade barrier. Nowadays, pesticides are being developed as per the principles of green chemistry. This is a welcome step. At the same time, it is vital to curb misuse, or rather abuse, of pesticides.

The author is former Professor and HoD, Entomology, Dr YS Parmar University of Horticulture and Forestry, Nauni (Solan), HP

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