5. Insects and Animal Pests that Harm the Tobacco Health

There are several insects pests in Tobacco. One important insect and a nematode pest in Tobacco are as follows:

Tobacco Leaf Caterpillar

Symptoms

Freshly-hatched larvae feed gregariously on leaves, scraping the leaf tissue and completely stripping the plant.

Older larvae disperse and feed voraciously on foliage at night. During the day, they usually hide in the soil around the base of the plants. Due to extensive feeding, only petioles and branches are left behind.

Larvae and adults thrive at temperatures between 15 and 35°C. However, they favor higher temperatures within this range.

Habitats and Reproduction

The damage is caused by the tobacco caterpillar, Spodoptera litura. Adult moths have grayish-brown bodies and variegated forewings with white wavy markings on the edges.

The hind wings are translucent white with brown lines along the margins and the veins. Females lay hundred of eggs in clusters on the upper leaf blades, covered with golden brown scales.

After hatching, the hairless light-green larvae disperse quickly and start feeding gregariously on leaves. Older larvae are dark green to brown with dark spots on the flanks.

Two yellow longitudinal bands run along the sides, interrupted by black triangular spots. An orange band runs dorsally between these spots. Larvae and adults thrive at temperatures between 15 and 35°C.

Leaves damaged by Tobacco Caterpillar.
Fig.3.Leaves damaged by Tobacco Caterpillar.

Prevention

Use tolerant varieties and sow early to avoid peaks in insect multiplication. Irrigate regularly to avoid prolonged mid season drought. Plant trap crops like sunflower, taro and castor oil plant around and within the fields.

Use light or pheromone traps to attract the Tobacco Caterpillar moths. Check your fields for signs of the insect such as egg masses, feeding damage or the presence of larvae.

Collect egg masses and larvae from trap crops or host plants and destroy them manually. Remove weeds 20-25 days after transplantation.

Handle your plants carefully during intercultural operation, avoid plant damage and injuries. Disinfect your tools and equipment in order to protect soil contamination.

Plow deep to open pupae to natural enemies and the sun heat.

Chemical Control

Always consider an integrated approach of preventive measures together with biological treatment if available.

Extensive insecticide use can lead to resistance development of the pest. Azadirachtin can be used during the egg laying stage and prevents the larvae from hatching.

To control the young larvae, several types of insecticides could be used.

For example Cypermethrin 10 EC @ 2ml/lit.

Baits solution also effectively reduces larvae populations.

Biological Control

Parasitoid wasps likeTrichogramma chilonis, Telenomus remus or Apanteles africanus parasitize or feed on eggs or larvae.

Bio-insecticides based on Nuclear Polyhedrosis Virus (NPV) or Bacillus thuringiensis also work as well. Alternatively, the insect pathogenic fungi Nomuraea rileyi and Serratia marcescens can be sprayed on leaves.

Bait solutions based on rice bran, molasses or brown sugar can be distributed on the soil in the evening hours.

Plant oil extracts of neem leaves or kernels and extracts of Pongamia glabra seeds are highly effective against Tobacco Caterpillar.

Root-knot nematode in Tobacco

There are 2 species of root-knot nematodes widespread on tobacco. 1. Meloidogyne incognita and 2.Meloidogyne javanica are most damaging. The latter is more tolerant to drought and high temperatures.

They are found almost in every tobacco producing country in the world.

Symptoms

Tobacco plants infested with root-knot Nematodes show stunted growth and yellowing of leaves. Root systems develop the characteristic knots or galls (swellings).

The severity of the symptoms depends on the number of nematodes. Plants heavily infected can develop symptoms characteristic of nutrient deficiencies.

In the field, infestation usually occurs in patches. Root-knot nematode causes high economic damage to farmers worldwide.

Aerial symptoms are not always present when nematodes are at a low level in the soil. At moderate to high populations, plants may appear stunted, yellow, and wilted (Figure 1).

Foliar symptoms are more severe under drought conditions because nematodes are directly impacting the plants ability to uptake water and nutrients as well as increasing secondary pathogens.

If removed from the soil, roots are seen having distinct swellings (galls, Figure 2) where female nematodes and egg masses can be found.

Roots may also have symptoms associated with root rotting pathogens like Fusarium wilt, Black Shank, or Granville Wilt.

Habitats and Reproduction

At optimal temperatures, the life cycle of Meloidogyne spp. takes about 37 days to complete. Temperatures vary slightly between the different species and the host in question.

Juveniles penetrate root tips and initiate the development of giant cells in root tissues, resulting in the characteristic galls.

The knots in the roots impair water and nutrient transport, causing the yellowing and wilting of leaves, as well as stunted growth.

Getting rid of the nematode by means of crop rotation is difficult because of the wide host range of Meloidogyne spp.

Prevention

A number of commercial crop varieties are resistant to some species of root-knot nematodes. Try crop rotation with non-host plants such as groundnut, sorghum, maize and millets.

Use cover crops that favor the buildup of nematode antagonists.

Chemical Control

Always consider an integrated approach with preventive measures together with biological treatments if available.

Successful approaches to control of nematodes rely on integrated pest management strategies. Nematicides containing carbofuran 5G, can be applied to the soil during land preparation and after 35 days of transplantation followed by irrigation.

Broadcast Dazomet pesticide such as Basamid at 1.5kg for each bed of 30 sq.m. Mix the chemical with soil by cultivating the bed using a new hoe across and along the bed 14 days before transplantation.

Cover with a black plastic paper. Alternatively you can use Metham sodium such as Herbifume should be drenched on the seedbed at the rate of 3 litres in 30 litres of water for a bed of 30 sq.m.

Drench the chemical 14 days before sowing. Cover with a black plastic paper for 14 days, after which you remove the black paper and cultivate the soil so that air can pass as well..

Biological Control

Poultry manure or organic waste is effective to control populations of root‐knot nematodes. Roots are less damaged, plants show more growth and fruit yield increase significantly.

Bacterial treatments of soils and seeds with bio-pesticides containing Pseudomonas Fluorescens, Pasteuria penetrans or Bacillus thuringiensis also work better.

Nematode-feeding fungi (Arthrobotrys spp. and Monacrosporium spp.) or fungi parasitizing on eggs and females (Pochonia chlamydosporia and Paecilomyces lilacinus) are alternative solutions.