Diseases and parasites of ornamental grasses.

Rust is one of the most common diseases, and one of the few that affect perennial grasses. It is caused by fungi of the genus Puccinia, Puccinia striiformis and Puccinia graminis, which thrive in humid conditions with temperatures ranging from moderate to warm. Rust can significantly weaken the plant if not properly treated. It hampers its photosynthesis.

Not all grasses are susceptible. It is found mainly on the Panicums, and the Phalaris.

Identification

Rust appears as small rust-coloured spots on the leaves of perennial grasses. These spots can vary in size and shape, but are generally round or ovate. As the disease progresses, these spots can merge to form larger areas of rust-coloured discoloration on the leaves, leading to slower growth.

A distinctive sign of rust is the presence of small rust-coloured pustules on the undersides of the leaves. These pustules contain fungal spores, which are dispersed by wind or water splashes, thereby promoting the spread of the disease.

The characteristic symptoms of rust

Natural treatment

Here are some natural solutions to combat rust:

1. Prune the affected parts: As soon as you identify leaves showing rust signs, prune them and remove them to prevent the spread of the disease. Be sure to disinfect your pruning tools between cuts to avoid contaminating other parts of the plant.
2. Spray horsetail decoctions: Horsetail decoctions are effective when applied regularly, every fortnight, possibly in combination with nettle manure.
3. Fungicides help neutralise rust. Use copper-based substances such as the Bordeaux mixture or sulphur.

Prevention

Some preventive measures for susceptible species can help:

1. Avoid excess moisture: Over-watering or prolonged moisture promote rust development. Water your plants appropriately and ensure the soil is well drained.
2. Water at soil level: Avoid wetting the leaves of perennial grasses, as moisture on the leaves promotes rust growth. Prefer watering directly at soil level.
3. Improve air circulation: Stagnant moisture promotes rust development. Ensure you plant your perennial grasses at an appropriate distance from each other to promote good air circulation.
4. Strengthen plant health: A healthy perennial grass is more resistant to diseases. Provide your plants with suitable soil for the species. Pay attention to drainage, soil richness or lack thereof, add compost if necessary, and ensure they receive enough sunlight. Horsetail decoctions and nettle manures mentioned in the treatment paragraph can also be used as prevention because they strengthen your plants and make them more resistant.

You can treat it with natural solutions based on sulphur or bicarbonate of soda, or even milk.

→ See Virginie’s Powdery Mildew article to learn the natural recipes to apply to your plant.

Prune the affected parts and burn them to prevent overwintering of the fungus.

Powdery Mildew

Powdery mildew manifests as white powdery patches on the leaves of grasses. To combat powdery mildew, use a mixture of water and bicarbonate of soda as a natural treatment or Bordeaux mixture.

Powdery mildew leaves a white powder on the leaves

Leaf Spots

Leaf spots are usually caused by excess humidity. Avoid overwatering, and if necessary, remove the affected leaves to prevent spread.

Prevention

Regarding prevention, practices such as good air circulation between plants, suitable soil, adequate fertilisation, appropriate watering, a horsetail spray, help reduce the risk of fungal diseases in grasses.

Other cryptogamic diseases affect lawn or forage grasses, but not ornamental grasses.