Identifying Hosta Diseases and Pests

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Hostas are remarkably resilient plants that have become a mainstay of the shade garden. When the basic needs of the plant are met: protection from direct sun (most varieties), ample watering, regular fertilization and division of mature stands, hostas are, for the most part, worry free. However, a few issues do exist that affect the health and aesthetics of the plant.

hosta pair

The hosta on the left is considerably smaller than its neighbor. Last year, both hostas were the size of the hosta on the right.

What we know about this situation:

  • Last year both hostas developed brown edges on their leaves by the end of the summer
  • The smaller hosta has wilted looking leaves
  • No moles or voles are present in the garden
  • The crown of the smaller hosta is firm
  • Watering is done by a bubbler that waters both hostas, but the gardener has not started watering the garden (as of late May)
  • The hostas are not fertilized

It is impossible to identify for certain what is causing this hosta distress from a photo. However, we can review these common hosta afflictions to narrow down the possibilities.

Common Hosta Diseases and Pests

Caused by a host of diseases occurring at once, anthracnose thrives in damp, still, part-to-full shade areas of the garden.

Signs: Tan or brown spots in the leaves that enlarge and develop dark borders. The spots drop out of the plant and the leaves take on a tattered look.

Action: Remove infected leaves, water with soaker hoses rather from above, replace mulch and ensure there is room for air circulation between the plants and treat with a fungicide to protect the remaining healthy leaves.

Petiole Rot
Formerly known as hosta crown rot, petiole rot is a serious fungal disease.

Signs: Yellowing and browning of the leaves around the margins, leaves become limp and mushy at the base of the petiole. The leaves are easily pulled from the main plant. White fungal threads (mycelium) may be visible. The disease fungus produces very small, round fungal seeds of sorts called sclerotia at the base of the petiole. Sclerotia can remain inactive in cold weather and are activated when the environment becomes warm and humid.

Action: Do not mound mulch around the base of the plant. Do not transplant any obviously infected plants or those you suspect may be infected. Remove infected tissue; taking care not to spread the fungus.

Helpful Hint: Have a container handy for immediate disposal and isolation of infected plant material.

Bacterial Soft Rot
Bacterial soft rot is caused by several types of bacteria and usually occurs where there is a wound caused from division or planting. Wounds may also be caused by ice or a colder than average winter that caused the ground to heave and thaw. Heaving and thawing is typical in clay soils.

Signs: Your nose will tell you that your hostas are suffering from bacterial soft rot. You will smell an offensive odor caused by the state of decay of the petioles and lower leaves.

Leaves will turn yellow in color.

Action: Remove and dispose of infected plants. Thoroughly clean any tools that came in contact with the plant as well as your hands and gloves.

Hosta Virus X

Hosta virus X is a vigorous spreader that may go undetected for years. The virus is often transmitted when cutting plants during which time the infected sap of one plant comes in contact with a new plant.

Signs: Mosaic, yellowing, tissue that looks thin and wrinkled. The colors of variegated leaves tend to blur together and lose their crisp definition.

Action: Use a discerning eye when selecting hostas. Destroy infected plants, thoroughly clean your tools and never divide an infected plant.

Foliar Nematodes

Signs: Older leaves develop light green to yellow stripes parallel to the major leaf vein. Affected leaves have a dry, tattered appearance.

Action: If you suspect foliar nematodes do not water plants from above. Splattering water spreads foliar nematodes. Remove and destroy leaves with dead areas. Burn or bury infected plant material.