Pests and Diseases

Potato aphid

Macrosiphon euphorbiae

Aphids are small, soft-bodied insects found on plants’ undersides. They come in various colours, secrete a sticky substance called honeydew, and can cause damage to plants. They can spread viruses like the Potato leafroll virus. Aphids are identifiable by the tubular structures called cornicles on their bodies.

To control aphid infestation, prune the affected areas, check transplants before planting, use tolerant plant varieties, use reflective mulches, spray with water to knock off aphids, and use insecticidal soaps or oils. Insecticides are needed only for high infestation levels. Check product labels before use.

Tuber moths

Mottled leaves due to sap-feeding and later yellow or bronze, resulting in yellow or brown patches.

Chemical control

Thrips

Feeding on seed, roots and seedling stems by larvae, and adults damage emerging seedlings.

Cultural practices to reduce population.

Seed treatment.

Nematodes

Adults chew on seedling stems, resulting in reduced stand.

Seed treatments.

Late blight

Phytophthora infestans

The disease begins as small green lesions on leaves and expands in cool, moist conditions to form dark brown to black lesions surrounded by chlorotic halos. It spreads to petioles and haulms, leading to plant death.

Seed certification, integrated management, and early planting of resistant cultivars reduce the need for intensive fungicide sprays and eliminate inoculum.

Bacterial wilt

members of the Ralstonia solanacearum species complex (RSSC)

Disease symptoms include young leaf wilting, stunted growth, chlorosis, and eventual death. Brown discolouration of vascular tissue in tubers is also observed, followed by rotting.

For healthy potato plants, use pathogen-free seed tubers, avoid cutting or dipping them, manage nematodes, plant resistant varieties, fumigate soil, rotate crops, treat irrigation water, and disinfect equipment.

Powdery scab and Root galls

Spongospora subterranea f. sp. subterranea (Sss)

Accurate identification of symptoms is crucial for the management and containment of two potato diseases: common scab caused by Streptomyces spp. and powdery scab. Although the symptoms of these diseases are difficult to distinguish, the conditions for disease development and control measures for each are different. Therefore, it is essential to be able to identify the symptoms accurately for effective management and control.

To reduce Sss disease, apply various management measures such as pathogen-free field selection, crop rotation, optimal plant nutrition, and post-harvest hygiene.

Soft rot

Erwinia carotovora

Water-soaked lesions on stems may grow to extended lesions from base to canopy. Tissue turns soft & slimy, brown to black. Leaves wilt & curl with a soft texture when wet.

Sanitise tools when cutting seed pieces. Avoid damaging tubers during harvest. Reduce leaf wetness by allowing leaves to dry after watering.