Insect Pest and Disease Management in Poplar Plantations

By:- Arshdeep Kaur and  Parminder Singh Tak

Poplars are amongst the fastest-growing tree species which can be harvested at short rotations of 8 to 10 years. Poplars with straight and cylindrical bole, moderate conical crowns, mostly deciduous during the winter season, easy vegetative propagation, high potential for trait manipulation through breeding, hemisphere-wide distribution and economically valuable wood and fiber makes it popular among agroforestry systems. Intensive cultivation of poplar hybrids in modern times made to succumb the poplar to various insect pests and diseases. Various attempts have been made to generate information on these pests. This article summarizes some important aspects of key insect pests and diseases of Poplar.

Insect pests of poplar

1. Leaf Defoliators (Clostera restitura & C. fulgurita)

Peak Period: July – November. Over-wintering occurs in the pupal stage.

Nature of damage: Moths appear sometimes during the months of March-April from overwintering pupae. The larvae are voracious feeders. The first and second instar larvae scrap leaf epidermis and skeletonize the leaf and the latter stage larvae eat away all the tissue of the leaves leaving the veins. The larvae are usually gregarious feeders upto 2nd to 3^rd instars but the latter stage larvae are solitary feeders.

Control: 

1. Collecting gregarious larvae and destroying them at nursery and sapling stages 

2. Collect and destroy yellow creamy egg masses laid on leaves by burning or crushing them. 

3. Plough the field 2-3 times in December to bury pupae in soil.

2. Leaf Webber (Asphadastis cryphomycha)

Peak Period: July – November

Nature of damage: The young larvae web 2 or 3 leaves with silken threads and eat the epidermis resulting in the drying of leaves. Pupation occurs in webbed leaves. The webbed leaf folds give a scorched appearance when seen from below.

Control: 

1. Collecting gregarious larvae and destroying them at nursery and sapling stages.

2. Collection and destroying of yellow creamy egg masses laid on the leaves by burning or crushing them.

3. Plough the field 2-3 times in winter to bury leaf folds with pupae in it.

4. Growing resistant poplar clones (L 47/88; L 48/89) to reduce attack of defoliator in nursery and subsequently in plantations 

3. Poplar Stem Borer (Apriona cinerea)

Peak Period: July – August

Nature of damage: 

In the nursery, the grubs bore and make galleries towards the roots, in older trees in the plantation through branches of the main stem and to the trunk. They make circuitous holes in the outer epidermis at an interval of 10 to 12 cm for throwing out their excreta and chewed wooden fibre. Each grub makes 8 to 10 holes. Ultimately all the grubs in different branches come down in the main trunk which is hollowed out inside. A number of grubs may be found on a single tree. An attack by this borer into the tree bole renders its timber unsuitable for any commercial use, as the entry of fungus and pathogens in the bored galleries causes discoloration of its wood and its becomes weak, offering little resistance to wind and gets broken by a modest gust. 

Control:

1. Prune the infected branches in August-September before larvae enter the main stem. 

2. Figure out all ejection holes of live infection in each tree and insert the iron wire into the hole to kill the insect and plug them with wet clay, leaving only lowermost hole untouched. 

3. Inject kerosene oil into this lowest hole. 

4. Avoid planting of other collateral hosts like mulberry, apple in the vicinity of poplar plantation.

4. Bark Eating Caterpillar (Indarbela quadrinotata)

Peak Period: July to October.

Nature of damage: The attack is more pronounced in block plantations than boundary plantations. The neglected plantations that underwent water scarcity during summer are more prone to attack. Repeated and severe attack by this insect for 2-3 years results in the complete death of plants. The larvae of the insect are usually nocturnal feeders. After hatching caterpillar feed on the bark and move towards the branches, make a hole at the base of the branches and penetrate inside. Sometimes larva penetrates through the young branches and moves towards the main trunk. Larva feeds internally for 9-11 months on the bark at night and makes covering with pieces of bark, fecal pellets and glued with saliva (silken). The larva makes L-shaped tunnels in the trunk usually at the joints of the branches. Pupation takes place inside tunnels. Overall, this pest affects the vigor of the trees.

Control: 

1. Collect and burn the loose bark, damaged bark and affected branches.

2. Irrigation of the plantation must be ensured in summer months. 

3. Plantation should be avoided near or mixes to/with fruit orchard (especially Litchi, Guava) or visa-vis.

4. Remove the web and inject kerosene oil into the holes. 

Diseases

The peak period for leaf spots is rainy season i.e. from July-September. Severe infection of leaf spots causes blightening and premature defoliation.

A. Myrothecium Leaf spots (Myrotheicum roridum) 

Symptoms:

Infection usually appear on lower leaves as round to oblong or irregularly shaped spots, which are light brown in centre with dark brown margins. The size of spots vary from 5 to 20 mm in diameter, which may coalesce to form bigger patches giving blightened appearance to the tree. The sporodochia appear concentrically on the upper surface of the spots, as raised rounded structures which are initially white and later turned olive green to black in colour. The necrotic area is shed giving shot hole appearance. 

B. Cercospora and Phaeoisariopsis Leaf spots (Cercospora populina and Phaeoisariopsis sp.) 

Symptoms:

Brown to dark brown round spots of variable sizes appear on leaves, the centre of which contains a dark speck giving a dot like appearance. The colour of the spots is same on both the sides of leaf. The spots coalesce to form bigger patches, to give blightened appearance.

C. Drechslera Leaf Spots (Drechslera maydis) 

Symptoms:

The disease starts as light brown coloured minute specks on lower leaves of the plant. These spots can be as large as 0.8mm in diameter. The spots are light brown coloured with dark margins and usually contain a yellow halo. Mature spots have target board ring type pattern. 

D. Alternaria Leaf Spots (Alternaria spp.) 

Symptoms:

The disease starts as purplish-brown spots with dark margins. These spots merge with each other to form large irregular patches with ill-defined concentric rings. 

Control of Leaf Spots:

A. Three to four sprays with Bordeaux mixture (0.8%) starting from the first week of July/ onset of monsoon and subsequent sprays at fortnightly intervals. 

B. Avoid raising nursery on same place where infection was observed in previous year.

C. In case of severe infection, collect the defoliated diseased leaves and burry or burn them. 

D. Proper sanitation by ploughing the plantation at fortnightly intervals help in quick decomposition of the litter and disease inoculum.

E. Cutting Rot (Botryodiplodia spp.) 

Peak Period: Cuttings planted in March when temperatures are high have highest incidence.

Symptoms:

Cutting rot is a serious disease of nurseries. It appear on the bark of newly planted cuttings, as raised black bodies called pycnidia, which contain millions of spores of the fungus. With the advancement of infection the tissue below the bark turns brown and is covered with black mass of the fungus. Ultimately the cuttings rot and bark appear as shredded fibers leading to the death of the plant. The problem aggravates in termite-infested soils. The disease intensity increases with any damage to cutting. 

Control:

a. Use cuttings made from healthy, disease-free nursery plants only. 

b. Treat the cuttings with Bavistin @ 0.5% by dipping them for 15 minutes before planting. 

c. Drench the soil around the cuttings with Bordeaux mixture (0.8%), if disease attacks the plant in nursery. 

d. Avoid growing poplar cuttings in water logged areas.

The writers are from the Department of Forestry and Natural resources, Department of Plant Pathology