| Disease (causal agent) | Symptoms | Survival of pathogen and effect of environment | Comments on control |
|---|---|---|---|
| Armillaria root rot * (Armillaria mellea) |
Symptoms are similar to crown rot but distribution in the field is different. Examination of affected plants reveals white fungus plaques beneath the bark at or below soil line on main stem. Erica canaliculata and E. hirtiflora have been infected. | Fungus survives for long periods in infected roots buried in soil. Infection is favored by the same conditions that are favorable for plant growth. | Avoid fields just cleared of oaks or other susceptible woody plants. This is not a common disease of heather. |
| Chlorosis (Iron deficiency) |
Foliage turns yellow and some turns almost white, especially new growth. Terminal growth may die and plants are stunted. Occurs if soil pH is too high. | Soils that are too basic as a result of too much calcium. | Spray plants with ferrous sulfate using 6 to 8 pounds/100 gal water. Thoroughly wet the plants using 100 to 150 gal/acre. Apply once a month starting in early spring as growth commences. If stems turn black, reduce dosage and frequency of treatment. Acidify soil. |
| Powdery mildew * (Erysiphe azaleae, Golovinomyces orontii) |
Shoot tips are reddened, then yellow and turn brown and fall off. A side bud develops into the new terminal and successive killing of the tips causes crooked, twisted growth. The white powdery mildew growth is often difficult to find. Affected plants are stunted and bushy. Erica persoluta is damaged. | On living heather foliage. Fungus is favored by moderate temperatures, partial shade, and dry foliage. | Several fungicides are available to protect foliage from infection. Start applications in spring and after each irrigation. During very hot periods, sulfur may damage foliage and flowers; avoid excessive rates of application. |
| Root and crown rot (Pythium spp. *, Phytophthora cinnamomi *) |
Plants are stunted or may suddenly wilt and collapse. Roots are killed and the base of the stem (crown) is attacked, causing a complete or partial girdling. Erica hirtiflora (=E. regerminans) and E. hyemalis are very susceptible. Erica canaliculata (E. melanthera) is moderately resistant and E. persoluta is resistant. | Soilborne pathogens with wide host range. These organisms also survive in infected plants. Favored by excessive soil moisture, poor drainage, and warm temperatures. | Avoid introduction into new areas by growing or obtaining disease-free plants. Take cuttings from high on the plant and use heat-treated or fumigated propagative and growing medium. Prevent infection in the nursery by periodic treatments with an oomycete (water mold) specific fungicide. Careful water management will provide some relief in field plantings. Oomycete (water mold) specific fungicides applied as a drench also helps. |
| Rust * (Uredo ericae) |
Small pustules of powdery orange spores occur on leaves. Infected leaves usually turn yellow and abscise. Erica hirtiflora and E. persoluta var. alba are infected. | On foliage. Spores are airborne and may be carried by the wind for many miles. Pathogen is favored by moderately low temperature and dew or rain. | Protect foliage with sulfur applied as a dust or spray. Start applications in late March and continue at 10- to 14-day intervals until rains stop. During very hot periods sulfur may cause damage to foliage and flowers; avoid excessive rates of application. Also avoid overhead watering. |
| Verticillium wilt * (Verticillium dahliae) |
Wilting, yellowing, and defoliation occur frequently on only one side of the plant. Examination of crown and roots, which appear healthy, helps differentiate this disease from root and crown rot. Symptoms usually first appear in early summer. Erica australis and E. persoluta are affected. | Fungus is soilborne and has a wide host range. Fungus invades plant in the cool spring plugging the water-conducting tissues. Symptoms occur when plant is stressed for water, particularly during warm periods. | Avoid fields that have been in susceptible crops or weeds such as tomato, chrysanthemum, strawflowers, nightshade, and others. Propagate plants, using heat or chemically-treated medium. The fungus can be eliminated from field soil by fumigation with chloropicrin or a chloropicrin combination. |
| * For additional information, see section on Key Diseases. | |||