Potato Aphid Control Comes Down to a Countable Threshold

Winged aphids move into potato fields first, ahead of the wingless colonies that build up once they've settled. UNPT (France) identifies three species as the ones to watch in potato crops: Myzus persicae, Aphis nasturtii, and Macrosiphum euphorbiae. The advisory frames close field monitoring as the prerequisite for any spray decision — not a calendar-driven routine, but a response to what scouting actually finds.

Ladybugs and hoverfly eggs are already present and active in fields, providing what the material describes as significant natural regulation of aphid populations. The guidance treats insecticide application as a fallback, triggered only once nuisance thresholds are actually reached, rather than a default response to any aphid sighting. Where treatment does become necessary, product choice still matters — TEPPEKI is named as a preferred option because it's compatible with beneficial insects, with use limited to BBCH stage 15 or earlier.

The threshold itself is specific: 5 to 10 aphids per leaf, or 50% of leaflets carrying at least one aphid, based on 40 leaflets sampled diagonally across the field. That precision matters — it replaces a subjective read on infestation pressure with a number any scout can reproduce, and it sets the bar high enough that isolated aphid sightings shouldn't trigger a spray on their own.

The recommended method is straightforward: on a leaf from the lower half of the plant, choose one of the two lateral leaflets next to the terminal leaflet, and check it for aphids. That single check is repeated 40 times across different plants in the field. If more than 20 of those 40 sampled leaflets turn up carrying aphids, the guidance calls for intervention with an appropriate insecticide.