Epidemiology and Control of Heuchera Rust

Heuchera rust, caused by Puccinia heucherae, was first identified within the UK in 2004. Since then, the incidence of the disease on nurseries has increased significantly on a range of species and varieties and it has been proving extremely difficult to control using a combination of fungicides and cultural control methods.

A range of species (H. americana, micrantha, sanguinea and villosa) are susceptible, as are individual varieties, including 'Marmalade', 'Lime Marmalade', 'Peach Flambe', 'Obsidian', 'Midnight Rose', 'Plum Royale', 'Plum Pudding', 'Southern Comfort', 'Chocolate Ruffles', 'Melting Fire', 'Palace Purple', 'Lime Rickey', 'Sugar Plum', 'Beauty Colour', 'Ginger Ale', 'Mocha', Key Lime Pie', 'Silver Scrolls'). In addition, it appears that micropropagated hybrids can be particularly problematic for growers. Heuchera rust is mainly seen on older stock, although symptoms can be seen on younger plants of more susceptible varieties.

A number of research and knowledge transfer priorities have been identified and the HDC intends to fund a two-year research programme to address these. The programme should focus on a balance of research and knowledge transfer activities. Work should build on current knowledge and not duplicate effort

Aims:

To investigate and improve the understanding of heuchera rust and its epidemiology, specifically;

• Determine the origin of the infection by heuchera rust
• Elucidate the conditions when heuchera rust is most likely to occur

Objectives:

Objective 1: Survey and review for further information relevant to heuchera rust incidence

 1.1 Survey heuchera growers to understand the pathway of disease introduction and conditions in which the disease is most likely to occur, including plant susceptibility, to guide investigations into the situations in which heuchera rust may appear.
1.2 Review global knowledge of heuchera rust and relevant epidemiological information from rusts on other hosts to guide investigations into conditions favourable to heuchera rust.

Objective 2: Determine if latent rust infection can be detected in heuchera from nurseries

2.1 Refine and apply a molecular test to confirm if the infection is due to Puccinia heucherae, or another rust species, and to detect the fungus on symptomless heuchera plants.
2.2 Apply the molecular test and collect and grow on heuchera plants to determine whether plants arriving at nurseries are infected.

Objective 3: Determine how differing irrigation periods may affect infection from rust pustules and if water demand affects symptom expression from latent infection

3.1 Study the effects of leaf wetness period and timing in the day on plant infection by rust.
3.2 Study the effect of different water regimes on expression of rust symptoms in heuchera.

Objective 4: Knowledge transfer

4.1 Prepare annual and final reports, an article for HDC News and updates to growers.

4.2 Present findings to growers and discuss outcomes at suitable HDC events.