# Nasturtiums — Blackfly & Caterpillar Control (bee-safe)
Steve's nasturtiums get wiped out every August by two pests. This page captures the diagnosis and the annual control plan. Context: nasturtiums grown in pots, soil reused yearly, watered via drip irrigation only in dry spells. Growth/flowering is fine — pests are the problem.
## The two attackers
### 1. Blackfly (black bean aphid, *Aphis fabae*) Tiny black insects clustered on stems, flower buds and undersides of leaves. Not butterfly eggs — butterfly eggs are laid singly or in pale/yellow clusters and don't crawl. Blackfly suck sap and coat the plant in honeydew → sooty mould, smothering and killing it.
Overwintering: black bean aphids lay eggs on spindle (*Euonymus europaeus*) and viburnum shrubs — NOT on nasturtiums and NOT in soil. Winged females fly in every spring. Steve has a viburnum (laurustinus, *V. tinus*) on the property — blue-black berry clusters, opposite evergreen leaves, reddish stems. That is the egg factory.
### 2. Caterpillars (cabbage white, *Pieris brassicae*/small white) Nasturtiums are a trap crop for cabbage whites too. Larvae peak in August. Eggs are clusters of tiny yellow eggs on leaf undersides.
## Annual control loop (all bee-safe)
| Enemy | Weapon | When |
| ——- | ——– | —— |
| Blackfly eggs on viburnum | Horticultural/plant-oil winter wash (Bug Clear Winter Wash / Vitax) | Jan–Feb |
| Blackfly founders | Squash first cluster + soap spray + ant barrier | June |
| Cabbage white eggs | Squash yellow clusters under leaves | July (weekly) |
| Caterpillars | Bt spray (XenTari) — repeat after rain / every 7–10 days | July–Aug |
| End of season | Rip out + bin infested growth (not compost), scrub pots | October |
### Key notes - Winter wash kills blackfly eggs on the viburnum twigs before hatch. Bee-safe (no bees in winter). - Ant barrier (grease band/sticky ring on pot rim or stem base) stops ants farming/protecting
blackfly — big lever everyone misses.
- Early colony squashing is the biggest single lever — stop the first generation in June and
the year collapses.
- Herbicide is the wrong tool for aphids — kills plants not insects, leaves residue. Don't use. - Soil reuse is fine — blackfly don't overwinter in soil. Tip out old roots, check for
vine weevil grubs (creamy-white C-shaped, brown head), top up but **don't fertilise** (nasturtiums flower best in poor soil).
## Bee-safe soap spray (recipe)
- 1 tsp (5 ml) pure liquid soap — castile (Dr Bronner's) or horticultural soap (Safers).
NOT Fairy/washing-up liquid (detergents strip leaf wax).
- 1 litre water (warm helps mixing). - Optional: 1 tsp vegetable oil for knockdown/sticking.
Use: spray at dusk (bees gone; dry+harmless by morning, no residual). Soak undersides, growing tips, flower buds. Repeat every 3–5 days for two weeks, then weekly while colonies active. Avoid open flowers (petal spotting, not bee harm).
## Soap vs XenTari — don't mix, alternate - Soap = blackfly (aphids), every few days while colonies active. - XenTari (Bt) = caterpillars only, every 7–10 days, after rain. Harmless to bees/adult
butterflies/birds.
- Avoid “Bug Clear Ultra” — acetamiprid (neonic), harms bees.