Chapter 7

Pests & Disease

Most hosta troubles in Ohio come from four animals and two pathogens. Knowing what does what makes diagnosis simple and the cures cheap.

The four animals

Slugs and snails

Far and away the most common hosta pest. They feed at night and hide under mulch and pots during the day. Damage shows as irregular ragged holes in the middle of leaves (not on the edges — that's a beetle), with a silvery slime trail visible in morning light. Thin-leaved cultivars get destroyed; thick-leaved blue cultivars are largely ignored.

Controls, in order of effectiveness:

• Iron phosphate pellets (Sluggo, Escar-Go). Pet-safe, rain-resistant, broadcast a thin layer around plants in early spring as noses emerge and re-apply every 3 weeks through May. By far the best modern option.
• Beer traps — shallow dish of cheap beer sunk to the rim, emptied every morning. Works, smells terrible, fills with dead slugs.
• Hand picking by flashlight an hour after dark. Effective for a small bed, tedious for a large one.
• Diatomaceous earth — only works dry; useless after dew or rain.
• Copper tape around individual pots — works, expensive at bed scale.

Avoid metaldehyde-based baits (older blue pellets). They are toxic to pets and wildlife and unnecessary now that iron phosphate exists.

Deer

Deer think hostas are salad. A herd that finds your bed will mow every plant to a 2-inch stub in one night and come back the next. The only reliable controls are physical barriers and rotation of scent repellents.

• An 8-foot fence is the textbook answer. Almost no one does this.
• Rotating two or three different scent repellents (Liquid Fence, Bobbex, Plantskydd) sprayed every 2–3 weeks — and after every rain — keeps damage to acceptable levels in most Ohio neighborhoods. The rotation matters; deer habituate to a single product within a season.
• Motion-activated sprinklers (Orbit Yard Enforcer is the well-known one) work surprisingly well, especially the first season.
• "Deer-resistant" cultivars don't exist. Tags that say so are aspirational.

Voles

Small rodents that tunnel under mulch and eat hosta roots and crowns from below. Symptoms: a healthy-looking plant suddenly wilts, and when you tug it, the whole top of the plant lifts off because the roots are gone. Damage peaks in late winter under snow cover.

Controls:

• Avoid deep mulch (over 4 inches) right against the crown — voles use it as a highway.
• Pull mulch back 6 inches from the crown in late fall.
• Mouse-style snap traps under a piece of bent-over hardware cloth, set in active runs, baited with peanut butter and oats. Cheap and effective.
• For prized specimens: plant the rootball inside a "vole cage" of 1/4-inch hardware cloth folded into a basket.

Rabbits

Mostly a problem on new growth in spring. Damage looks like a clean 45-degree slice through stems and leaves (rabbit teeth leave a knife cut; deer leave a torn shred). Liquid Fence works on rabbits too; a 2-foot chicken-wire ring around emerging plants works better.

The two pathogens that matter

Hosta Virus X (HVX)

An incurable, infectious viral disease that spreads via sap on cutting tools, dividing knives, even on contaminated soil. It is the single biggest disease threat to hosta collections. Symptoms vary by cultivar but include:

• Ink-bleed pattern — dark green pigment streaking along veins, looking like spilled ink that ran out from the midrib
• Lumpy, deformed, or oddly-twisted leaves
• Stunted, unthrifty growth that worsens each year

There is no cure. An infected plant must be dug up — roots and all — and bagged for the trash. Do not compost. Sterilize any tool that touched the plant with a 10% bleach solution before touching another hosta. Wash your hands and gloves.

Prevention: buy from reputable nurseries that test their stock, inspect new plants closely before planting, and never accept divisions from a friend's garden if you've ever seen ink-bleed there.

Crown rot (Sclerotium rolfsii / Petiole rot)

A soil-borne fungus that hits in hot, humid weather. Symptoms: petioles soften and collapse, leaves yellow and fall outward from the crown like an opened umbrella, and a white cottony mycelium with small tan "mustard seed" sclerotia appears at the soil line.

If caught early, dig the plant, cut away all affected tissue with a clean knife, dust the cuts with sulfur or cinnamon, and replant in a different, drier spot. If the crown is gone, the plant is gone — discard, do not compost, and avoid replanting hostas in that exact spot for at least two years.

Prevention is drainage, drainage, drainage. Crown rot lives in soggy soil. A raised bed and a 2-inch mulch gap from the crown will prevent almost every case.

Foliar nematodes — the minor menace

Microscopic worms that live in leaf tissue and produce angular brown lesions bounded by leaf veins — the damage looks geometric, almost like brown stained glass. They spread in water splash. Manage by removing affected leaves and avoiding overhead watering. Severely-infested plants should be discarded.