Tomato-potato psyllid isn't just another sap-sucker to tolerate the way you might aphids or whitefly. First found in New Zealand in 2006, it carries a bacterium that causes real, sometimes serious damage to tomatoes, potatoes, capsicums and tamarillos, all in the same plant family, which makes early detection worth more effort than it would be for a purely cosmetic pest.
The adult is small, about 3mm, and easy to mistake for a tiny cicada or leafhopper at a glance: pale to dark brown with clear wings held roof-like over its body. The nymphs are the stage most people actually notice first, flat, scale-like, greenish-yellow discs stuck to the undersides of leaves, often surrounded by small white granules that look faintly like sugar or salt. That waxy granular residue is one of the more reliable early signs, visible before any real leaf damage shows.
The bacterium the psyllid can carry, not the feeding itself, is what does the real harm. In potatoes it causes zebra chip, dark striping inside the tuber that shows up clearly when fried and makes the crop unsellable, though a home gardener growing for the table rather than the market is affected differently: yield drops and the plant's overall vigour suffers. In tomatoes, infected plants show yellowing or purpling leaves, stunted new growth and poor fruit set, symptoms that look similar enough to a nutrient problem that psyllid is often ruled out too late.
The bacterium the psyllid can carry, not the feeding itself, is what does the real harm.
Check the undersides of leaves regularly through the warmer months, particularly on tomatoes and potatoes, rather than waiting for obvious plant-wide symptoms. Yellow sticky traps hung near susceptible plants catch adults early and give a genuine warning sign before nymphs establish in numbers. Once numbers are high, insecticidal soap or a targeted spray applied to leaf undersides is the standard home-garden response, but by that point some yield loss for the season is usually already locked in.
That's really the core problem with tomato-potato psyllid: by the time it's obvious, some of the damage is already done. Premium check-ins on this site are timed to a plant's actual growth stage rather than a fixed schedule, precisely so a pest like this gets flagged while it's still a few scattered nymphs on a leaf underside, not a season's yield already compromised.