Dahlias in Oregon: Planted to show off late-season blooms

Dahlias in Oregon: Planted to show off late-season blooms

Diseases and pests of dahlia

Diseases

Dahlias are susceptible to bacterial, viral and fungal diseases. Most diseases appear when a pathogen is present and the plant is stressed due to environmental factors or care.

If the dahlias you grow are infected with a bacterial or viral disease, discard the plant and tubers. To avoid spreading these diseases to other dahlia plants, do not fertilize affected plants or tubers. Sterilize all tools by dipping them in bleach.

One of the most common bacterial diseases is crown gall, which is identified by a cluster-like extra growth or multiple growths on the crown of the tuber. You can find pictures of this disease in the Pacific Northwest Management Guide. Coronary gallbladder is not treatable and spreads easily. If you suspect that the tuber is infected with crown gall, discard it. Sterilize all tools used on the affected plant before using them on other dahlia tubers.

Stunted growth, yellow streaks or spots on the leaves often indicate viral diseases. Both the plant and tuber can host viruses. There is no cure for dahlia viruses. If you notice symptoms of the virus on your plant, remove the plant, as viruses can also spread. Dahlia mosaic virus is one of the most common viral diseases of dahlias. Learn more about how to diagnose and treat this virus in Dahlia Mosaic Virus: An Illustrated Guide to Symptoms and Diagnosis.

Powdery mildew is a common fungal disease that affects dahlia plants and can be identified by a gray powdery substance on the leaves. You can often prevent fungal diseases such as powdery mildew with proper plant maintenance. To prevent fungal diseases, water at the base of the plant rather than above it. Air circulation is also important to control fungal diseases. If part of the plant is infested with fungi, remove any infected leaves and reduce overcrowding to increase airflow to the plant.

Insects and predators

Aphids, cucumber beetles, earwigs, and slugs are some of the common insects that may affect your dahlias. Several comprehensive resources for identifying and managing these insects are listed below.

  • Aphids are common on plants. You can treat them with insecticidal soap. Spray dahlia buds and leaves during cool times of the day.
  • Cucumber beetles are light green with black spots. The cucumber beetle chews the leaves, flowers and stems of dahlia plants. Cucumber beetles can be difficult to control, but some gardeners have success using trap crops as well as some insecticides.
  • Earwigs come out at night and harm flower blossoms. Organic and conventional traps help eliminate earwigs.
  • Slugs and European garden snails attack young dahlia plants at night. Apply the graft two weeks after planting or when the first shoots appear.
  • Voles, mice and gophers will eat dahlias. Voles can use mole runways to access tubers. Gophers create their own tunnels. Baiting is the best control.
    (Tags for translation)Dahlia

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