Ramularia is a widespread fungal disease affecting various crops globally, posing a significant challenge in agricultural production. This pathogen can cause substantial damage, particularly to cereal crops. Understanding this disease is crucial for effective management.
What is Ramularia
Ramularia is a genus of fungi, with Ramularia collo-cygni commonly affecting barley. This fungal pathogen affects a range of crops, including barley, oats, wheat, and grasses. It primarily manifests as a foliar disease, impacting the leaves of infected plants. The fungus lives inside the plant without visible symptoms, a phase known as endophytic growth, before becoming aggressive.
Identifying Ramularia Infections
Identifying Ramularia infections involves observing specific symptoms on plant leaves. The disease begins as small, irregular brown “pepper spots” on lower leaves during tillering, or on upper leaves around flowering. These spots develop into distinctive rectangular, reddish-brown lesions, 1 to 3 mm in size. Lesions are restricted by leaf veins and often surrounded by a light brown or yellow halo.
As the disease progresses, spots can merge, leading to larger necrotic (dead) areas that reduce grain yields and quality. Symptoms can also appear on awns and leaf sheaths.
How Ramularia Spreads and Thrives
Ramularia spreads through fungal spores primarily dispersed by wind and rain splash. The pathogen also survives on infected seeds and crop residues from previous seasons, serving as a source of infection for new crops. Favorable environmental conditions for Ramularia include high humidity, prolonged leaf wetness, and moderate temperatures. Spores are typically released 24 to 48 hours after leaves are wet, and infection occurs through the plant’s natural pores (stomata). The fungus produces toxins, such as rubellin D, which react with light to damage leaf tissue, especially on upper leaves receiving more sunlight.
Managing Ramularia Disease
Managing Ramularia disease requires a combination of strategies to minimize its impact. Cultural practices are important for prevention:
Rotating crops with non-host plants helps break the disease cycle by reducing pathogen survival in crop residues.
Planting resistant or tolerant varieties can reduce disease severity.
Optimizing planting density ensures good air circulation within the canopy, reducing leaf wetness conducive to fungal growth.
Proper irrigation techniques that avoid prolonged leaf wetness also prevent disease.
Chemical control involves the use of fungicides. Preventative sprays before symptoms appear, typically during the booting stage (growth stages 45-49), are most effective. Later applications, after symptoms develop on upper leaves, are less effective.
While some fungicides, such as certain SDHI-azole combinations, are effective, resistance to various fungicide groups has been observed, making integrated approaches more relevant. Consulting local agricultural experts for product recommendations and application guidelines is advisable, as regulations and resistance patterns vary by region. Combining cultural and chemical methods offers the most effective and sustainable approach to Ramularia management.