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Aphids (Order: Hemiptera) are among the most damaging agricultural pests worldwide. In Southern Africa, key pest species include the green peach aphid (Myzus persicae), cabbage aphid (Brevicoryne brassicae), cotton aphid (Aphis gossypii), and Russian wheat aphid (Diuraphis noxia).
Beyond direct feeding damage, aphids transmit numerous plant viruses including Potato Virus Y (PVY), Cucumber Mosaic Virus (CMV), and Barley Yellow Dwarf Virus (BYDV). A small aphid population can cause disproportionate yield loss through virus transmission.
Aphids are soft-bodied, pear-shaped insects 1–3 mm long. They cluster on growing tips, undersides of leaves, and flower heads. Watch for:
Inspect at least 25 plants per field, checking growing tips and leaf undersides. Note the presence of natural enemies (ladybirds, lacewing larvae, parasitised mummies) before deciding to treat.
| Active Ingredient | IRAC Group | Notes |
|---|---|---|
| Imidacloprid | 4A (Neonicotinoid) | Systemic; excellent for aphid colonies; soil/foliar |
| Thiamethoxam | 4A (Neonicotinoid) | Fast knockdown + systemic activity |
| Dimethoate | 1B (Organophosphate) | Broad-spectrum; good contact + systemic |
| Pirimicarb | 1A (Carbamate) | Selective aphicide; spares beneficials |
| Lambda-cyhalothrin | 3A (Pyrethroid) | Contact only; quick knockdown |
| Spirotetramat | 23 | Systemic; moves in phloem; good for buried colonies |
Neonicotinoid resistance is a growing concern in many aphid populations. Avoid consecutive applications of Group 4A products. Rotate with organophosphates, pyrethroids, and selective aphicides.
Conserve natural enemies by selecting selective products (pirimicarb) where populations are sustainable. Preserve beneficial insect habitats around fields.
