Peanut scab

The fungus survives on crop debris, in the soil, and on infected seeds, making it a persistent threat in regions where crop rotation is not strictly followed.

Infection spreads through conidia, which are disseminated by rain splash, wind currents, and mechanical activities. This allows the disease to propagate rapidly throughout a field under favorable weather.

Once the conidia land on the host tissue, the fungus penetrates the epidermis, triggering localized tissue growth and eventually creating the signature scabby or crusty lesions on the plant surface.

The disease is host-specific to the genus Arachis, meaning it does not typically jump to unrelated crops, but it can persist indefinitely if wild peanut species are present nearby.

Early symptoms appear as tiny, circular, or irregular brown spots on leaves, petioles, and stems. These spots often develop a darker margin as they mature.

The most distinctive symptom is the formation of corky, scabby growths on the surface of infected organs. These lesions may become raised and rough, resembling a crust or a scab.

Severe infestations lead to the curling and premature drop of leaflets. Stems may become twisted or distorted, which significantly hinders the plant's structural development and vigor.

When the pathogen attacks the reproductive structures, the pods may show brown, necrotic patches or distorted shapes, rendering them visually unappealing and poor in quality.

Under conditions of high humidity, a delicate gray-white mold, consisting of fungal spores, can often be observed on the surface of the lesions, especially on the underside of the leaves.

The development of Elsinoë arachidis is heavily dependent on moisture. It thrives in high humidity and frequent rainfall, with optimal temperatures for infection ranging from 20°C to 28°C.

Densely planted fields that lack adequate airflow create a stagnant, humid microclimate, which is highly conducive to the germination and spread of fungal spores.

Morning dews and lingering fogs provide the necessary water films on leaves required for the fungus to initiate successful infection of the plant tissues.

Overhead irrigation systems often accelerate the disease spread by mimicking rain, splashing spores from the soil or infected debris onto healthy plant parts.

Poor soil management practices, such as failing to incorporate crop residues or planting in fields with high previous infection history, increase the disease pressure significantly.

The primary damage is caused by the reduction of photosynthetic leaf area, which weakens the plant and limits its capacity to produce oil-rich kernels.

Infection of flowers and pods leads to significant yield losses, as the fungus interferes with the development and maturation of the peanuts within the shells.

Harvested kernels from severely infected plants may have reduced commercial value, making them unsuitable for high-quality food processing or export markets.

In cases of heavy outbreaks, yield reductions can range from 30% to 50%, posing a serious economic threat to small-scale and large-scale peanut farmers alike.

Moreover, the stress caused by the fungus makes the crop more susceptible to secondary opportunistic pathogens, further weakening the field health.

Effective management begins with a long-term crop rotation strategy, where peanuts are not grown in the same field for at least 3 to 4 years to break the infection cycle.

Deep plowing and proper burial of crop residues after harvest are essential to remove the primary source of overwintering inoculum from the soil surface.

Using high-quality, certified seeds and applying effective fungicide treatments before planting can significantly reduce the risk of early-season infections.

During the growing season, monitoring is key. If symptoms appear, applying copper-based or systemic fungicides can help suppress the spread of the fungus.

• Maintain proper plant spacing to improve air circulation and reduce humidity.
• Remove any wild peanut relatives or weeds that could serve as hosts.
• Avoid overhead irrigation where possible to keep the foliage as dry as possible.