Woolly Apple Aphid (Eriosoma lanigerum) and its Management

Introduction

In India, the insect was reported in 1889 from Conoor district of Tamil Nadu and 1909 from Shimla (H.P.). Presently, it has spread all apple growing areas of India. It is serious pest of apple, pear and crab apple (Pyrus baccata)

 Symptoms of infestation

·  The infested plant pale green leaves and whitish cottony patches on the stem and branches.

·   The galls or Knots are formed on the roots and other underground portions of the plants.

Nature of damage

The nymphs and adults suck the sap from branches twigs and roots. They keep on moving from aerial parts to root zones and vice versa. Owing to the loss of cell sap, twigs shrivel and young nursery plants may die quickly. Due to the galls or knots, the nutrient uptake is hindered, which cause nutritional imbalance, thereby affecting the vitality of the trees adversely. Besides, the galls/ knots may split, which act as entry points for many other pest and disease pathogens. The infested plants remain stunted with greatly reduce bearing capacity. The fruits from the severally infested trees are of poor quality, remain under sized, malformed and insipid in taste.

Life Cycle

The pest is most active during March to September and multiplies at a reduced pace during October to November. The development from December to February is extremely slow. The woolly apple aphids reproduce parthenogenetically and the progeny, thus produced consists of females only. Each female may produce up to 116 young ones in one lifetime at the rate of 1-4 nymphs per day in March- April, 1-5 in May- July, 1-6 in August, and only 1-2 per week in winter months. There are four nymphal instars and duration of each varies according to the season. The total duration of nymphal period is 35-42 days in February, 29.5 days in August- November, and 10.5-19.5 days in April- July. The winged forms appear in July- September when fresh colonies on new plants or branches are initiated. There may be 13 generations in one year. In December, there is a partial migration from aerial parts to the roots of infested plants and the reverse migration from the roots to the aerial takes place in May.

How to manage the pest

The management of this pest in apple orchard is a difficult task. This is due to presence of waxy covering on the body of insect and due to local migration to the roots. However, good success can be achieved if following strategies are followed:-

• At pre-plantation stage, woolly apple aphid resistant root stocks can be used. For example; Golden delicious, Northern Spy, and Morton root stocks 778, 779, 789 and 793.

• In the Himachal Pradesh, the woolly apple aphid is controlled by using natural methods. The natural enemy/ parasite of this pest is Aphelinus mali (Haldeman), an exotic parasitoid; which attacks the 4^th and 5^th instar nymphs. The parasite has to be maintained on cut twigs fixed in moist soil inside wire gauze cages.

• The aphids parasitized by Aphelinus mali do not have woolly strands and looks like black mummies. Twigs having such mummies without exit holes should be tied to other twigs to enhance the activity of the parasite.

• Keep the tree basins always clean.

• Remove the suckers or water sports regularly.

• Cover the cracks or crevices, wounds and cut ends with fungicides or insecticides.

• The main source of this pest in the orchard is plant nurseries. So, select the healthy plants from the nurseries and treat them with chlorpyriphos 0.05 percent before plantation.

• During leaf fall, the infested plants can be sprayed with 2.0 ml of chlorpyriphos 20EC in 200 litres of water per ha (i.e. 400 ml per 200 litre of water) or quinalphos 0.05% 25EC (2ml/L). It should be sprayed in winters.

• For controlling the root infestations, drenching with 1.0 ml of oxy demeton methyl 25EC per litre water per ha (i.e. 200 ml per 200 litre of water for drenching) can be applied. These chemicals should be applied in winter months.

• During the summer months i.e. one month before harvesting, spray 200 ml of malathion 50 EC in 200 litres of water can be sprayed. The insecticidal spray should be avoided where the parasitoid Aphelinus mali is present. 

• For underground roots, fumigation with paradichlorobenzene granules in a 15 cm deep  trench dug round the infested tree, about 2 meters from it. 

• As per recommendations in Packagae of Practices issued from Himachal Pradesh Horticulture Development Project, the granules of phorate (30g Thimet) or Carbofuran (50g Furadan 3G) at 5cm depth in rizosphere during April-May.