Aphids on Chrysanthemums: Why Pyrethrum Doesn't Protect Your Plants

Finding black, sesame-seed-shaped aphids on your garden chrysanthemums? They're unaffected by the plant's natural chemistry because you're not growing the pyrethrum source species. Garden mums are Chrysanthemum coccineum, while commercial pyrethrin comes from Chrysanthemum cinerariaefolium, grown in Kenya, Tanzania, and Ecuador.

The insecticide is made by harvesting and drying flowers, then grinding petals into a fast-acting but short-lived powder. For your aphid problem, a strong blast from the garden hose knocks most off effectively.