Tobacco
Tobacco Hornworm
Manduca sexta
Insect
In a Nutshell
- External feeding and holes in leaves.
- Missing leaves.
- Dark dropping.
- Presence of caterpillars.
Can also be found in
Tobacco
Symptoms
Caterpillars feed on young leaves and growing shoots, creating visible holes and external damage. Their presence is marked by dark droppings on the leaves. If you inspect the plant closely, you may see the green or brown caterpillars themselves. Caterpillars can eat all the leaves off a tobacco plant, leaving only the stem and main veins. During extensive outbreaks, entire fields can be left completely defoliated. With tomatoes, heavy infestations can result in the caterpillars feeding on the developing fruit, leaving behind large, open scars on the fruit.
Recommendations
Organic Control
Use Bacillus thuringiensis (Bt) products according to the label and local guidelines. Bt is a bacterium that kills the caterpillar when ingested, and is safe for organic farming. Additionally, natural predators like birds, small mammals, ladybugs, lacewings, and parasitoid wasps help reduce hornworm populations. If you find any tobacco hornworms on your plants, remove them by hand while wearing gloves, and place them in a bucket of soapy water to kill them.
Chemical Control
A number of chemical insecticides exist for management of tobacco hornworm and other caterpillars. Malathion, diazinon, carbaryl, and fenitrothion are pesticides that target various stages of insect development, but they are particularly effective against the actively feeding caterpillar. When using pesticides or any chemical product, it is important to wear protective, including eye protection, and carefully read the label instructions. Regulations vary by country, so ensure you follow the specific guidelines for your area. This guarantees safety and increases the chances of successful application.
What caused it?
The symptoms are caused by insects. These insects feed only on solanaceous plants, most commonly on tobacco and tomato. The caterpillar can grow to the length of an adult's index finger and has a red or black "horn" at the end of its body. The caterpillar is usually green but can also be brown and has seven diagonal white stripes on each side of its body and a blue-black eyespot on each side of its body. The female tobacco hornworm moth lays her eggs on the leaves of a host plant. They usually will not lay eggs on plants that caterpillars have already eaten from. The egg hatches and the caterpillar feeds on the leaves and stems of the plant. The caterpillar moults its skin several times until the resting stage, during which the caterpillar transforms into an adult moth. The resting stage is found below ground or deep in the leaf litter.
Preventive Measures
- Select resistant tobacco cultivars if available in your area.
- Do not plant too late; this might expose your young plants to insects from other fields.
- Apply the right amount of nitrogen fertilisation, avoiding excess, to promote healthy growth without encouraging pests.
- Check your crop for any signs of infestation or health issues, especially the young leaves and shoots.
- After harvesting, manage insects in the soil to avoid problems in the next two years: cut secondary stems of tobacco plants, dispose of them out of the field and then plough.
- Quickly remove the stalks after harvesting to leave the field clean.
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