Psyllids are often overlooked insects that cause a plant condition known as psyllid yellows, the result of toxic saliva injected by the insect. Be on the lookout for these insects on your tomatoes and potatoes.
Watch for the eggs and nymphs on the backs of leaves of tomatoes and potatoes. Eggs are small (one-thirty second of an inch), orange-yellow and supported by small stalks. Beneficial lacewings have similar eggs but are larger, white and on longer stalks. Psyllid eggs take 6 to 10 days to hatch into nymphs.
The nymphs look like flat plastic discs attached to stems or the backs of leaves. They are yellow at first but become green and well camouflaged as they mature. The nymphs don’t move once they settle down to suck plant juices. They excrete small, waxy beads of white “psyllid sugar” as they feed for 2 to 3 weeks. The presence of “sugar” on plants is a good indicator of psyllids.
The adults are rarely seen and are green at first but rapidly turn dark. Adults fly to new plants to lay eggs. Four to seven generations are produced in a growing season.
Symptoms on potato and tomato plants are similar. Yellowing or purpling along leaf midribs and leaf edges is concentrated in top leaves. As the disease progresses, the yellow-green or purple-red color spreads to the entire top growth and growth slows. New top leaves often remain small and tend to stand upright giving the top an almost feathery appearance.
When psyllids attack tomato plants early, effects can be so severe that little fruit is set. Infestations later in the growing season on larger plants cause only a small yield loss. If psyllids attack potatoes before tuber set, many small tubers form. Later attacks reduce growth and cause irregularly-shaped potatoes that may sprout prematurely underground before harvest.
Because the psyllid insects are small, stationary and camouflaged, they go unnoticed until the damage is well underway. Watch for psyllid sugar and turn leaves over to look for nymph “discs.” If found, take action right away.
If your plant is affected, do all you can to get plants growing vigorously and put on size early (fertilize as recommended). If pesticide control is desired, permethrin or esfenvalerate (two synthetic pyrethroid-products) and pyrethrum (organic) are insecticides labeled for and available to homeowners. An alternative is sulfur dust if leaf undersides can be coated. Two percent insecticidal soaps (ex. Safer® brand) provide useful if more erratic control.
Psyllids may infest but cause insignificant damage to eggplant, peppers, and other vegetables in this same family.