Swift Farmer: Here Is How To Beat Potato Pests & Pocket Millions

By Frank Kamuntu

Learning how to identify insect potato pests helps us to decide on a course of treatment.

Taking a close look at the most important of the more than 60 insect pests that attack potatoes will help potato farmers to protect their crops and income.

POTATO TUBER MOTH

• The moths are nearly 1 cm long, and the wings are greyish, with dark grey spots.
• They are active at night and hide between the plants during the day.
• Moths live for about a week and lay up to 250 eggs.
• Potato tuber moth larvae damage foliage and tubers beneath the ground, as well as tubers in storage.
• The moth does not feed on the potato plants, but lays her eggs on or near them.
• The resulting larvae tunnel or mine into all plant parts, causing severe yield losses when the tubers are reached.
• When the foliage dies down, usually at the end of the season, the larvae move down cracks in the soil to reach the tubers.
• They tunnel into the tuber just beneath the skin. In storage the eyes (where the sprouts form) are usually attacked first, and there is no sprout development.
• This can lead to severe losses in stored seed potatoes.
• Various insecticides have been registered to control this pest.

POTATO LEAF MINER

• The leaf miner is the larva of a small fly that also attacks a wide range of other vegetables.
• The female fly damages plants by piercing leaves with her ovipositor, causing “stippling”.
• These “punctures” may also stress plants.
• The female lays her eggs in some of the puncture marks.
• A small cream-coloured maggot hatches from an egg and starts to mine between the leaf surfaces.
• Severe infestation (leaf mining by the larvae) may give leaves and haulms a burnt appearance and usually results in foliage dying off prematurely.
• This “removal” of green material before the plant is ready to die off results in a yield reduction of up to 70%.
• The larvae don’t attack tubers. Several registered insecticides help to control this pest.

APHIDS

• These are small insects with sucking mouthparts.
• They don’t usually damage plants directly, but are virus vectors that possibly transmit viral diseases when they arrive in a potato field after feeding on infected plants elsewhere.
• After multiplying in such a field, offspring that have fed on an infected plant may spread the virus to other plants in the same field.
• The 2 most important potato viruses are potato leafroll virus (PLRV) and potato virus Y (PVY).
• Tubers infected with such viruses may not be sold as certified seed.

CUTWORMS

• The cutworm moth lays eggs on the soil or lower parts of the plant.
• The young larvae feed on plants during the day, but as they get older they are usually found below the surface of the soil.
• From here they eat through the stems, causing the plant to die. If you dig into the soil next to a dead plant you will probably see the larvae.
• Sometimes cutworms move down much deeper and attack tubers when they find them.

MILLIPEDES

• Millipedes eat mainly dead or dying plant material.
• They don’t tunnel into the soil but may damage tubers if they reach them through cracks or when they come across exposed tubers.
• You can reduce millipede problems if you ridge often to ensure that all cracks and exposed tubers are covered.
• Although you can buy millipede poison baits, control is rarely needed.

BOLLWORMS AND LOOPERS

• These are the larvae of night-flying moths.
• The African bollworm attacks many crops and is very destructive.
• Moths lay many single eggs on plants and they hatch in a few days.
• The larvae have a characteristic white to beige stripe along both sides of the body.
• Larvae can grow up to 3 cm in length.
• They eat leaves and sometimes flowers, but this is usually only a problem when there are many larvae feeding in a field or when the plants are still small.
• Loopers walk by arching their backs and moving their back “legs” towards their front legs.
• Young larvae eat leaf surfaces between the veins; older larvae eat holes in leaves.
• They are usually only a problem when many caterpillars attack small plants at the same time.

NEMATODES

• These microscopic, slender roundworms live in the soil.
• Nematodes attack roots and tubers, and negatively influence the transporting of water and nutrients through the plant.
• In South Africa, the 3 most important nematodes that attack potatoes are: root knot nematodes, lesion nematodes and potato cyst nematodes.
• Root knot nematodes are the most common.
• They prefer a hot climate and sandy soil and survive in the soil for many years in the form of small eggs.
• The eggs hatch when a host plant grows close to them, and they move through moist soils to reach the roots.
• Infected tubers make galls which house the female worms and egg sacs.
• Planting infected tubers introduces nematodes into clean soils.
• Fallow cultivation, rotation with cereals or grasses and applying nematicides are some of the control measures.
• Lesion nematodes are less common but can cause economic losses.
• Infected tubers look unhealthy: they could have purple-brown pimples, pustules or wart-like protuberances.
• Potato cyst nematode infections must be reported to the SA Department of Agriculture as it is a quarantine pest.

MITES

• Red spider mite is the best known mite on potatoes.
• Females lay their eggs on the underside of leaves and the infestation is spread to other plants by wind, humans and moving machinery.
• They prefer warm, dry conditions, and their feeding causes white, yellow, silver or brown lesions.
• Mites attack leaves as well as stored potatoes.
• If not controlled, they can destroy plants in fields and stored tubers in a matter of weeks.