Most pest advice tells you to look for the insect itself, which is exactly the wrong approach for tomato-potato psyllid in its first week. The nymphs are tiny, flat, pale and sit motionless on the underside of leaves, genuinely easy to miss even when you're looking directly at them. What's much easier to spot, and what almost nobody tells a beginner to actually look for, is what the nymphs leave behind: psyllid sugar.
Psyllid sugar is a real, specific term used by New Zealand growers and garden centres, not a cute nickname invented for this article. As nymphs feed on sap, they excrete honeydew coated in a waxy layer, and it comes out as small white, granular crystals rather than a wet, sticky film the way aphid honeydew does. Scattered across the underside of a leaf, or on the leaf below where nymphs are feeding above, it genuinely looks like somebody spilled a few grains of caster sugar. Once you've seen it once, it's hard to miss again.
Psyllid sugar is a real, specific term used by New Zealand growers and garden centres, not a cute nickname invented for this article.
This matters because it shows up before the damage does. Yellowing, stunted growth and the leaf curl TPP is known for are all later-stage signs, and by the time they're visible, a colony has usually been established for a while. Psyllid sugar, by contrast, can appear while numbers are still low, which is exactly the window where mesh, a hose, or an early Tamarixia release actually gets ahead of the problem instead of playing catch-up.
The habit worth building is simple: when checking a tomato, capsicum or potato plant, tip the leaves over and look at the undersides specifically, not just glance at the top of the plant from standing height. Sooty mould, a black fungal growth that colonises honeydew, is a related but later sign, since it needs a build-up of sugar to grow on in the first place; catching the sugar itself means never getting to the sooty mould stage at all.
It's a small habit that pays off disproportionately, since a psyllid population that's caught while it's still just a scattering of sugar granules is a five-minute fix, and a population caught after it's built up for a month is a much bigger job. This site's premium check-ins prompt exactly this kind of leaf-underside look at the point in a plant's growth when it actually matters, rather than leaving it to be noticed only once the sugar has turned into sooty mould and curled leaves.