Pest identification
What's eating my ageratum houstonianum 'blue horizon'?
Spider mites (two-spotted)
Signs: Yellow-bronze stippling on upper leaf surfaces; fine webbing on undersides; flower quality drops as infestation worsens.
Control: Spray neem oil or miticide on leaf undersides; water consistently; remove and bag the most affected stems.
Whitefly
Signs: White clouds when plants disturbed; nymphs on leaf undersides cause yellowing and sticky honeydew deposits.
Control: Yellow sticky traps; insecticidal soap or pyrethrin sprays; inspect undersides weekly.
Aphids
Signs: Dense colonies on tender shoot tips and flower clusters; sooty mould and distorted growth follow heavy infestations.
Control: Water jet; insecticidal soap spray; encourage ladybirds and hoverflies in the garden.
Caterpillars
Signs: Ragged holes in leaves; flower clusters damaged; caterpillars hide among the dense, fuzzy flower heads.
Control: Hand-pick at night; Bt spray applied to all plant surfaces; remove debris where moths might lay eggs.
Keep ageratum houstonianum 'blue horizon' pest-free
Healthy plants resist pests best. Get the basics right:
- What eats hawaii blue flossflower — the species this cultivar belongs to
- What's wrong with my plant? — the diagnosis apps compared
- Common ageratum houstonianum 'blue horizon' problems & fixes
- Ageratum houstonianum 'Blue Horizon' watering schedule
- Ageratum houstonianum 'Blue Horizon' light requirements
- Full ageratum houstonianum 'blue horizon' care guide
Ageratum houstonianum 'Blue Horizon' pests — FAQ
What is eating my ageratum houstonianum 'blue horizon'?
Ageratum 'Blue Horizon' is troubled mainly by spider mites and whitefly in warm summers, with aphids attacking new growth. Caterpillars occasionally chew leaves and flower clusters. Two-spotted spider mite is the worst offender, causing rapid bronzing of foliage and decline of the fluffy blue flowers that are this variety's hallmark.
How do I get rid of spider mites (two-spotted) on ageratum houstonianum 'blue horizon'?
Yellow-bronze stippling on upper leaf surfaces; fine webbing on undersides; flower quality drops as infestation worsens. Spray neem oil or miticide on leaf undersides; water consistently; remove and bag the most affected stems.
How do I get rid of whitefly on ageratum houstonianum 'blue horizon'?
White clouds when plants disturbed; nymphs on leaf undersides cause yellowing and sticky honeydew deposits. Yellow sticky traps; insecticidal soap or pyrethrin sprays; inspect undersides weekly.
How do I get rid of aphids on ageratum houstonianum 'blue horizon'?
Dense colonies on tender shoot tips and flower clusters; sooty mould and distorted growth follow heavy infestations. Water jet; insecticidal soap spray; encourage ladybirds and hoverflies in the garden.
How do I get rid of caterpillars on ageratum houstonianum 'blue horizon'?
Ragged holes in leaves; flower clusters damaged; caterpillars hide among the dense, fuzzy flower heads. Hand-pick at night; Bt spray applied to all plant surfaces; remove debris where moths might lay eggs.