Dahlia: holes eaten in leaves

What it is likely to be on dahlia

1. Slugs and snails

   Candidate 1very common on this plant

   ·source

   Sourced guidancehigh confidence

   • Royal Horticultural Society: Slugs and snails

   Checked 2026-08-13

   The most destructive garden pest in a wet British spring, and the one surrounded by the most confidently repeated advice that does not work. They shred seedlings overnight and leave irregular holes with slime trails nearby.

   Points towards it

   • · a dried slime trail is conclusive and nothing else leaves one
   • · damage starts on the lowest leaves, nearest the ground the slugs come from
   • · an outdoor problem almost entirely

   Argues against it

   • · slugs are not an indoor problem in any normal circumstance — this rules it out entirely.

   Check this next

   Go out after dark with a torch and look at the underside of the leaves and the soil around the crown. Slugs feed at night, so an inspection at midday finds the damage and never the animal.

   What to do now

   Check at night and remove what you find, and clear the leaf litter and pot bases they shelter under during the day. On hostas, moving the plant into a container raised off the ground removes most of the pressure without any treatment at all.

   ·source

   Sourced guidancehigh confidence

   • Royal Horticultural Society: Slugs and snails — control

   Checked 2026-08-13

2. Capsid bug

   Candidate 2common on this plant

   ·source

   Sourced guidancehigh confidence

   • Royal Horticultural Society: Capsid bugs
   • Agriculture and Horticulture Development Board — AHDB: Capsid bugs on ornamentals

   Checked 2026-08-13

   A fast-moving green or brown bug, 6mm long, which feeds on shoot tips and is almost never seen doing it. What it leaves is unmistakable once the sequence is understood: it kills small patches of tissue in a leaf still folded in the bud, and as the leaf expands those patches tear into ragged holes with brown edges, so the finished leaf looks chewed and distorted while the plant never had a caterpillar on it.

   Points towards it

   • · the feeding happens in the bud, so only leaves that were unfurling at the time are marked — the older leaves below are clean
   • · the holes have brown papery rims and irregular torn edges, because they are expanded dead patches rather than bites
   • · finding nothing is genuine evidence here — the insect leaves before the damage shows, and every competing explanation leaves something to find

   Argues against it

   • · damage confined to mature leaves cannot be capsid, which can only mark a leaf that has not yet expanded — this rules it out entirely.
   • · a visible chewer or a slime trail is a simpler explanation for a hole

   Check this next

   Look at the edge of one hole with a hand lens. A capsid hole has a dry brown rim and a torn outline because the leaf grew apart around dead tissue; anything eaten has a clean green edge where the tissue was cut.

   What to do now

   Leave it alone on an established plant, or pinch out the worst shoot tips. The insects have almost always gone by the time the damage is noticed, so treatment lands on damage that has already finished, and the growth behind the ruined tips is unaffected.

   ·source

   Sourced guidancehigh confidence

   • Royal Horticultural Society: Capsid bugs — control

   Checked 2026-08-13

Narrow it down

This page lists everything at once, which is the right shape for reading and the wrong shape for deciding. The interactive tool asks one question at a time, starting with whichever would separate these causes fastest, and stops as soon as further answers would not help.

Opens with the plant and the symptom already set. Nothing you answer is stored or sent anywhere — the answers live in the address bar and nowhere else.

What this does not cover

These are the causes GrowingHQ holds rules for on dahlia — not every cause there is. Where several problems look alike, the honest answer is often that they cannot be told apart by eye, and a page that named one would be guessing. If none of the above fits, the general holes eaten in leaves page lists causes across all plants, and the Dahlia profile lists the problems it is prone to.