Lupins are stars of summer borders, with their upright spires adding height and drama. But if you’ve noticed yellowing leaves or flutters of tiny insects when you brush past, whitefly may be to blame. Don’t worry, there are safe, proven ways to tackle them and keep your lupins looking their best.
Understanding Whitefly on Lupins
The main culprit in UK gardens is the glasshouse whitefly (Trialeurodes vaporariorum). Although more common in greenhouses, they can become a nuisance outdoors in warm, dry summers, especially on soft-leaved perennials.
These insects:
- Suck sap, weakening plants and stunting flowers.
- Excrete sticky honeydew, which encourages black sooty mould.
- Multiply fast. Up to 12 generations in a single season in sheltered spots.
Symptoms on Lupins
Look out for:
- Yellowing, curling, or mottled leaves.
- A sticky residue on foliage.
- Clouds of tiny white insects flying up when disturbed.
- Black sooty mould forming on upper leaf surfaces.
Whitefly Control – Proven Methods for Lupins
1 – Biological Controls – Natural Predators
- Encarsia formosa: A parasitic wasp that lays eggs inside whitefly pupae. Used widely in RHS greenhouses.
- Effective when temperatures are consistently above 17°C.
- Ladybirds and lacewings: Feed on both adult whiteflies and their larvae. Attract them with pollinator-friendly planting nearby (e.g. dill, yarrow, cosmos).
2 – Insecticidal Soaps
- Insecticidal soap sprays: Break down the insect’s waxy coating, causing dehydration.
- Target the undersides of leaves where whiteflies lay eggs.
- Use soft water (hard water reduces efficacy) or rainwater if possible.
3 – Sticky Yellow Traps
- Yellow mimics leaf colour, attracting whitefly.
- Place above or near lupins. Particularly useful in greenhouses or sheltered patios.
- Replace weekly; traps become ineffective once coated.
4 – Physical Barriers
- Use fine insect mesh if growing lupins in raised beds or containers.
- Remove infested leaves – especially older lower leaves.
- Jet blast with water in the early morning to dislodge whitefly, followed by soap spray.
5 – Cultural Practices
- Avoid overfeeding with nitrogen: It produces soft, sappy growth that attracts whitefly.
- Rotate lupin locations annually in beds and borders.
- Encourage air circulation – whitefly thrive in still, warm air pockets.
6 – Companion Planting
- Marigolds (Tagetes) – Emit limonene, which repels whitefly.
- Nasturtiums – Work as sacrificial plants, drawing whitefly away from lupins.
- Basil or mint – Their strong scents can interfere with whitefly detection mechanisms.
Professional Tip: Biological Synchronisation
If using Encarsia, apply before infestations peak. These parasitoids need a host population to thrive, but can’t catch up if whiteflies are already widespread.
What Not to Use
- General pyrethroids: While effective short term, they kill beneficial insects, and whitefly often develop resistance.
- Homemade vinegar sprays: Often touted online, but can burn foliage and disrupt leaf pH.
Long-Term Resilience: Boost Lupin Health
Healthy lupins resist pests better. Ensure:
- Well-drained, slightly acidic soil.
- Full sun exposure.
- A spring mulch of compost to boost microbiota and fungal resistance.
Summary
| Method | Application | Best For |
|---|---|---|
| Encarsa formosa | Parasitic release | Greenhouses or warm, sheltered gardens |
| Sticky Traps | Passive monitoring | Early detection |
| Companion Planting | Intercropping | Repellence and distraction |
| Jet-washing and Pruning | Immediate control | Heavy infestations |
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Frequently Asked Question
1- How do I know if whitefly is affecting my lupins?
Look for yellowing or curling leaves, sticky residue on foliage, or tiny white insects flying up when disturbed. Black sooty mould on leaves is another common sign.
2 – What is the best way to get rid of whitefly on lupins?
Use a combination of methods:
- Biological controls like Encarsia formosa.
- Insecticidal soaps targeting leaf undersides.
- Sticky yellow traps for monitoring.
- Water jets and pruning for immediate removal
3 – Can companion planting help reduce whitefly on lupins?
Yes. Marigolds, nasturtiums, basil, and mint deter whitefly or act as sacrificial plants. Plant them near lupins to help confuse, distract, or repel pests naturally.
4 – Why are sticky yellow traps effective against whitefly?
Whiteflies are attracted to yellow because it mimics foliage. Sticky traps catch adults, helping reduce populations, especially in greenhouses or sheltered spots. Replace traps weekly for best results.
5 – How can I prevent whitefly on lupins in the future?
Promote strong, resilient plants by:
- Avoiding high nitrogen feeds.
- Improving air circulation.
- Practising crop rotation.
- Mulching in spring to boost soil health. Healthy lupins are less attractive and more resistant to pests.
David Domoney is a Chartered Horticulturalist, Broadcaster, and Author. David has worked with a number of the UK’s leading garden retailers as a plant buyer and strategic consultant. With more than 30 years experience, in horticulture, David is as passionate about plants now as he was when he bought his first plant at a village fete.
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