Crown Rust in Lawns

Crown Rust thrives in conditions which are warm (20 degrees C +) and humid, and the infection is carried from plant to plant by windborne spores. The spores land on new grass leaves and if there is sufficient surface moisture, will start to germinate and infect the leaf. Much more troublesome in Oat and Barley crops than in grasses, the fungus will grow through without killing the grass plant in most cases. The only exception to this would be when a whole lawn has become overwhelmed by Crown Rust.

Crown Rust is characterised by small orange, powdery pustules, on both sides of the leaf. The orangey rusty spores come away readily, and will cling to any boots, clothing or machinery brushing against, so it is easy to accidentally spread the spores across the lawn. As the name implies, the fungus only affects the tips or crowns of the grass leaves, leaving the roots untouched. Lawns that are left to grow too long become at greater risk of rust, with more regular mowing often cutting off any infected leaves before they have a chance to spore.

Fungicides have been suggested as a solution to Crown Rust. However, as with many other fungal conditions, our view is that they are of limited use on this type of adversary. Our experience is that the pustules will disappear once the grass has grown out. Grass which is low on nutrients will be particularly vulnerable to Crown Rust attack, so an application of a High-Nitrogen fertiliser will help the grass plants grow the fungus out.

Farmers have been encouraged to grow White Clover in the areas of grass they grow for silage, as it will fix the Nitrogen from the fertiliser into the soil. This Nitrogen is then absorbed by the grass plants, making them less susceptible to the Crown Rust spores. This is obviously less than attractive as a solution for domestic lawns though!

Scientists have been crossbreeding new grass varieties which are resistant to Crown Rust, which will eventually filter through into the marketplace, but our advice is to not panic at any cost because the problem is never too severe in UK lawns and is unlikely to be long lasting. Avoid the temptation to spray your lawn with ineffective fungicides and try feeding your lawn with a high-nitrogen fertiliser instead. Ride out the storm and let nature do the rest.