Peanut witches' broom

Peanut witches' broom is a devastating plant disease caused by phytoplasmas, which are specialized wall-less bacteria that colonize the phloem tissue of their hosts. These pathogens drastically alter the hormonal balance of the plant, leading to systemic disruption of growth and reproductive processes.

The primary host for this disease is the peanut plant (Arachis hypogaea). However, these phytoplasmas have a relatively broad host range, infecting various weed species and other legumes. These non-crop hosts play a critical role as natural reservoirs, allowing the disease to persist in the agricultural environment throughout the year.

The disease is characterized by extreme proliferation of shoots, resulting in a bushy, broom-like appearance of the plant. Symptoms include severe dwarfing, shortening of internodes, and the development of small, yellowing leaves. Infected plants typically fail to produce normal pods or seeds, rendering the crop economically worthless.

Transmission occurs exclusively through insect vectors, primarily leafhoppers (Cicadellidae). The insects acquire the phytoplasma by feeding on the phloem sap of an infected plant. Once the pathogen colonizes the salivary glands of the insect, it is transmitted to healthy plants during subsequent feeding events, facilitating rapid spread across fields.

Management and prevention strategies focus on breaking the disease cycle:

• Effective weed management to remove reservoirs of the phytoplasma surrounding the peanut fields.
• Chemical control of leafhopper populations using systemic insecticides during peak infestation periods.
• The use of certified healthy seeds to prevent the introduction of pathogens into new areas.
• Early detection and roguing of infected plants to reduce the inoculum load in the field.
• Implementing crop rotation and barrier cropping to disrupt the migration of insect vectors.