Peanut Crop Health: Recognizing and Managing Diseases

Peanut Scab (Sarna)

Symptoms

Characterized by small, brown spots with depressed centers on leaves. Corky, canker-like lesions are also observed on petioles, stems, and spikes.

Control

Fungicides are commonly used for scab control.

Peanut Rust (Raya)

Symptoms

Characterized by the presence of orange to brown pustules on the underside of leaves, which converge with age to cover the entire leaf in severe attacks. Infection is also common on petioles and stems.

Impact

Damage increases when it coincides with a severe disease outbreak. This disease is not typically considered an economically limiting problem for groundnut cultivation in the CBA region.

Net Blotch (Mancha en Red)

Symptoms

Presents as brown patches with diffuse, rather gray margins. When conditions are favorable, the disease develops rapidly. The characteristic net-like pattern is more prominent on the upper surface of the leaflets.

Leaf Scorch (Quemaduras en Hojas)

Symptoms

Injured leaves turn brown at the tip and margins of the leaflets, extending to cover half or more of the foliar surface. Fungal fruiting bodies are observed on these affected areas and can share the same lesion.

Phyllosticta Leaf Spot

Symptoms

Characterized by rather circular spots, light brown in the center and darker at the periphery, which can coalesce.

Environmental Conditions

This disease typically occurs early in the crop cycle.

Anthracnose

Symptoms

Appears as numerous patches of variable size and shape, distributed on the upper surface of leaflets, often starting from the margins. While typically no defoliation is observed, severe attacks can lead to it.

Impact

Severe attacks can cause significant defoliation and even seedling death.

Root and Crown Rot

Causal Agents

Caused by fungi such as Sclerotium rolfsii and Rhizoctonia solani.

Symptoms

Type 1: Sclerotium rolfsii

Produces symptoms of rapid wilting of a branch. Leaflets become chlorotic and then necrotic. The infection progresses through branches and adjacent areas, affecting the entire plant, including pegs and pods.

Type 2: Rhizoctonia solani

Characterized by a gradual disintegration of the roots, starting as elongated necrotic spots. On the stem at ground level, dry, sunken, dark brown areas appear and extend along the stem.

Favorable Conditions

Optimal conditions for their growth include temperatures between 19-36°C and moderate soil moisture.

Epidemiology

• Sclerotium rolfsii: Damage intensifies as autumn progresses and during the fruiting stage (late February onwards).
• Rhizoctonia solani: Affects plants at different stages of development, both pre- and post-emergence.

Impact

Damage caused by this disease becomes more manifest and widespread as autumn progresses, particularly when plants are in the fruiting stage, from late February onwards.

Diseases Affecting Roots, Stems, and Fruits

Symptoms

Initially observed on pods as extended, slightly sunken, light brown or black lesions.

Epidemiology

Manifests on developing fruits, including pegs, as well as on mature pods.

Control

Control of the causes of these diseases is challenging, as the pathogens are often facultative parasites that remain in the field through resistant forms or by living saprophytically on plant debris.

Recommended Control Measures:

• Prepare the ground appropriately, avoiding planting in areas with poor organic matter.
• Avoid the formation of a "plow pan" or compacted layer to ensure normal water drainage and air circulation.
• Practice crop rotation.
• Use good quality seed.
• Maintain clean cultivation by hoeing weeds.
• Avoid excessively deep planting, which can predispose stalks to attack.