Sharp Eye Spot in Cereals: Understanding, Identifying, and Managing This Subtle Fungal Threat

What is Sharp Eye Spot?

Sharp Eye Spot, caused by the fungus Rhizoctonia cerealis, is a subtle but increasingly recognized disease affecting all cereal crops. Though often confused with the more aggressive Eye Spot disease, Sharp Eye Spot is genetically unrelated and generally less severe in terms of yield loss. That said, under specific conditions—particularly in cooler climates—it can still cause noticeable damage.

Symptoms and Identification

The disease gets its name from the sharply defined elliptical lesions that resemble an eye, often with a dark border and a shredded epidermis. These lesions can occur higher up the plant stem (up to 30 cm), unlike traditional Eye Spot, which affects the base. Severe cases can lead to lodging and whiteheads in cereal crops.

Sharp Eye Spot lesions often look like scale insects have been removed, creating clear, dark marks—especially visible on the stem sheaths.

How It Spreads and Survives

Sharp Eye Spot overwinters as fungal mycelium on stubble and certain grass weeds. In spring, it can also spread via sclerotia, dense fungal structures that act as spore reservoirs. These infections are necrotrophic, meaning the fungus kills plant cells to feed on them, unlike biotrophic fungi that feed off living cells.

The disease thrives in cool, sandy, and slightly acidic soils, with optimal development seen around 9°C. Rhizoctonia can sometimes behave saprotrophically, living off decaying organic matter before infecting the plant—posing challenges in no-till systems.

Global Relevance and Varietal Susceptibility

Though less problematic in the UK, Sharp Eye Spot has emerged as a significant concern in countries like China and Chile. Yield losses are typically low (0.5%) but can spike up to 25% in extreme cases. Some Chinese wheat varieties like Wenmai-6 have shown higher susceptibility.

To date, no widely available resistant cereal varieties exist.

Biological Insights: Chitin and Zinc

The fungus secretes metalloproteases and polysaccharides that suppress the plant’s defence mechanisms. Interestingly, while zinc is generally toxic to fungi, Sharp Eye Spot uses trace amounts of it to power its infection enzymes—a curious biological twist.

Chitinase production by the plant is key to resisting infection. At Eutrema, chitosan-based products are used to flood the plant with chitin mimics, activating plant defences before the pathogen can shut them down.

Management and Control Strategies

While fungicide application is rarely economical due to low yield impact, cultural and biological methods can help manage the disease:

• Increase Soil pH: Liming acidic soils reduces fungal viability.
• Use Potassium Silicate Sprays: These strengthen cell walls and raise foliar pH.
• Promote Crop Health: Robust plants can outgrow early infections.
• Rotate Crops and Manage Grass Weeds: Reduce overwintering inoculum.
• Use Chitosan-Based Biostimulants: Enhance natural defenses through early signaling.

Conclusion: Why Sharp Eye Spot Still Matters

Despite its relatively minor impact in most temperate climates, Sharp Eye Spot is a disease worth monitoring—especially with changing weather patterns and more regenerative practices reducing tillage. It’s a reminder that subtle pathogens can become major players under the right conditions.

For growers looking to integrate advanced biological tools like chitosan or potassium silicate into their cereal management programs, Eutrema offers expert guidance and proven products.

Article by Dr Russell Sharp

Want more updates on crop pests and diseases? Listen to the Cereal Killers podcast or request a copy of our new Biologicals Program for cereals.

Download our Fungicide Reduction Action Plan here

Stay informed. Stay ahead.

Cereal Killers Podcast: https://t.co/eSEbBkTVHl

Hydroponics Daily Podcast: https://open.spotify.com/show/207T7p7fw9sPjINfSjVXW2