Gray leaf spot
Pyriculria grisea
What is a Gray leaf spot (Pyricularia grisea)?
Gray leaf spot, caused by the fungus Pyricularia grisea also known as Magnaporthe grisea, is a destructive disease. It manifests as small brown spots that expand into elongated or oval lesions with depressed gray centers and irregular brown edges. The infection can spread to the leaf sheaths, spikes, and stems, forming brown to black lesions. Grey leaf spot thrives in warm and humid climates.
How does the Gray leaf spot (Pyricularia grisea) occurs?
Gray leaf spot reproduces through the production and dissemination of spores by the fungal pathogen. The spores are typically spread through wind, rainwater, and human activities such as mowing or other turf maintenance practices. Once the spores land on the grass blades, they germinate, penetrate the plant tissue, and initiate the disease cycle, leading to the development of gray leaf spot symptoms.
Symptoms
1 - Impact on Plants
• Gray leaf spot can cause significant losses in crop yields, impacting crops such as rice and corn. • Infected plants exhibit weakened health, stunted growth, defoliation, and increased susceptibility to other stress factors.
2 - Soil Health
Severe outbreaks can affect nutrient cycling and decomposition of infected plant debris, impacting soil health and nutrient availability.
Solutions
1 - Preventions
• Choose less susceptible plants to gray leaf spot. • Avoid excessive nitrogen fertilizer applications that promote lush growth. • Properly manage irrigation to prevent prolonged leaf wetness. • Implement good turf management practices, including proper mowing, fertilization, and irrigation, to promote healthy plant growth and minimize stress.
2 - Treatment
Effective fungicides for gray leaf spot management include: • Strobilurin (QoI) fungicides: Examples include Insignia and Heritage. • Sterol inhibiting (DMI) fungicides: Examples include Banner Maxx 1.3ME. • Contact fungicides: Chlorothalonil can be effective when moderate to low disease pressure. Remember to always read and follow the label instructions of the fungicide product you use. • Rotate fungicides with different modes of action to minimize the risk of developing resistance in the pathogen population.
