Zonal geranium pests, webbing or sticky leaves: causes and what to do
6 results in the diagnosis tree begin with pests, 5 of them marked likely when the answers fit. They are ordered here for Zonal geranium (Pelargonium zonale), using what its sources say about pests and diseases and humidity and 6 problems recorded for it.
Sources last read 18 September 2026.
Pelargonium zonale is a species of Pelargonium native to southern Africa in the western regions of the Cape Provinces, in the geranium family. It is one of the parents of the widely cultivated plant Pelargonium × hortorum, often called "geranium", "horseshoe geranium", "zonal geranium" or "zonal pelargonium". Wikipedia, CC BY-SA 4.0
Native range: Cape Prov. to KwaZulu-Natal (subtropical). Also sold as horseshoe geranium and zonal pelargonium.
What Zonal geranium’s sources say that bears on this
- Pests and diseases
- Aphids, fungus gnats, thrips, caterpillars, leafhoppers and vine weevil can attack it. Disease risks: a virus, Pelargonium rust, grey moulds, and root and foot rots where soil is wet.RHS · read 13 September 2026
- Humidity
- ASHRAE recommends indoor relative humidity between 30% and 60%Penn State Extension · read 13 September 2026
How this shows up on a Zonal geranium
Holes chewed in the leaves, with droppings: a caterpillar pest
Holes and ragged edges appear on the leaves of the zonal geranium, with small dark droppings on the leaves below. Some leaves may be rolled or tied with silk.
RHS lists caterpillars among the pests it may attract. They grow fast and eat more as they grow, so damage accelerates.
Telling it apart: Whether tissue is missing. Chewing pests remove it; sap-feeders only discolor it.
RHS · read 13 September 2026Irregular notches bitten from leaf edges by an insect pest
The plant rocks loose in its pot and droops, and the root ball holds curled white grubs among chewed roots.
RHS lists vine weevil among the pests it may attract. Grubs hatch in the potting mix and eat the roots out of sight, so a plant in a pot can collapse with little warning.
Telling it apart: Whether the plant is loose. Grub damage leaves a plant that lifts from its pot with few roots.
RHS · read 13 September 2026Silvery streaks with black specks on the leaves: thrips
Silvery flecks and streaks spread over the leaves of the zonal geranium, peppered with tiny black dots. Flowers may open marked or misshapen.
RHS lists thrips among the pests it may attract. They feed on leaves and in flowers, and hide in buds, which makes them hard to spot.
Telling it apart: Whether the marks are silver. Thrips leave a sheen; sun scorch leaves dry, bleached tissue.
RHS · read 13 September 2026Small insects that jump when the leaves are disturbed
Pale mottling spreads across the leaves of the zonal geranium, heaviest near the veins.
RHS lists leafhoppers among the pests it may attract. They suck sap from the undersides, which leaves pale dead cells on the surface above.
Telling it apart: Whether the insects jump. Leafhoppers leap; whitefly flies up in a cloud.
RHS · read 13 September 2026Sticky buds and shoot tips crowded with small insects
Green, black or pale insects crowd the soft tips and buds of the zonal geranium. New leaves curl, and white cast skins collect below.
RHS lists aphids among the pests it may attract. Colonies build within days on young shoots, and the honeydew they shed makes the leaves sticky.
Telling it apart: What the white bits are. Aphids leave papery cast skins; mealybugs leave wax with an insect inside.
RHS · read 13 September 2026Tiny dark gnats rising from the potting mix
Small dark flies hover around the zonal geranium and run over the surface of the potting mix. The larvae, thin and white with black heads, live in its top layer.
RHS lists fungus gnats among the pests it may attract. They breed in the top layer of wet potting mix; on an established plant they are mostly a nuisance, on cuttings and seedlings they damage roots.
Telling it apart: Whether the leaves are sticky. Gnats leave none; sap-feeding insects do.
RHS · read 13 September 2026Possible causes, likeliest first for a Zonal geranium
Most likely aphids
Ranked higher because Zonal geranium's recorded problems point this way.
- Sticky buds and shoot tips crowded with small insects RHS
Why: Aphids cluster on soft new growth and flower buds, where the sap is easiest to reach.
What to try:
- Rub them off with fingers, or rinse them off in a sink or shower.
- Repeat every few days while new ones appear.
What would settle it: Look for the pale shed skins among the insects. Aphids molt as they grow, and the skins are left behind in the colony.
Most likely fungus gnats, which point at wet potting mix
Ranked higher because Zonal geranium's recorded problems point this way.
- Tiny dark gnats rising from the potting mix RHS
Why: Fungus gnats lay their eggs in moist potting mix, and their larvae feed on organic matter and fungi in it.
What to try:
- Let the top two inches of potting mix dry between waterings; the larvae need it wet.Useful: moisture meter
- Yellow sticky traps near the soil catch the adults and show whether the numbers fall.Useful: sticky traps
What would settle it: Put a slice of raw potato on the soil for a day. Tiny translucent larvae on the underside confirm them.
Most likely spider mites
Why: Spider mites feed on individual leaf cells, and each emptied cell shows as a pale speck.
What to try:
- Move the zonal geranium away from other plants.
- Wash the leaves, top and underside, with a strong spray of water in a shower or sink.
What would settle it: Hold a sheet of white paper under a leaf and tap the leaf. Tiny specks that move across the paper are mites.
Less likely for a Zonal geranium, still possible
Questions
- What usually causes pests on a Zonal geranium?
- For Zonal geranium: aphids, fungus gnats and spider mites.
- How can I tell which one it is on my Zonal geranium?
- What can you see? Fine webbing, and tiny pale speckles on the leaves; White, cottony tufts in the leaf joints; Small brown or pale bumps on stems and leaves that do not move; Clusters of small, soft insects on the new growth; Tiny dark flies around the soil; Sticky, shiny residue, but no insect I can see.
- What do Zonal geranium's sources say about its pests and diseases?
- RHS: Aphids, fungus gnats, thrips, caterpillars, leafhoppers and vine weevil can attack it. Disease risks: a virus, Pelargonium rust, grey moulds, and root and foot rots where soil is wet.
- What does this look like on a Zonal geranium?
- Holes and ragged edges appear on the leaves of the zonal geranium, with small dark droppings on the leaves below. Some leaves may be rolled or tied with silk. Telling it apart: Whether tissue is missing. Chewing pests remove it; sap-feeders only discolor it.
- Is Zonal geranium safe to handle while I check it?
- Its sources list it as toxic to cats and dogs. Wash your hands after handling the roots or sap, and keep trimmings away from pets.
Other plants that show pests
African violetIrregular notches bitten from leaf edges by an insect pest
Barberton daisyCurled, sticky new leaves with green or black insects: aphids
Bearded irisRagged holes and slime trails: a slug or snail pest
Bigleaf hydrangeaClusters of small soft insects on the shoot tips and buds: aphids
Bird of paradiseDull, finely mottled leaves and faint webs: spider mites
Blue passion flowerPale stippled leaves and tiny moving dots underneath: a mite pest
Something else wrong with the Zonal geranium?
What this does not cover
This page orders a decision tree's results using a plant's sourced care. It has not seen your plant, its pot or its window, and two problems at once are common: that is the usual reason a confident answer turns out wrong. The questions in the diagnosis tool narrow it further than a list can.