BOULDER COUNTY – There’s a pest that shows up now and again that does so much damage to tomatoes and potatoes that gardeners shudder whenever you mention its name. Like ghost stories around a campfire, we tell tales of the last time the insect showed up in high numbers, and scare each other with dire predictions of when it will next arrive.
Sadly, that ghost story has come to life. Potato/tomato psyllids are back and ready to wreak havoc on our love apples. Tomatoes top the list for most kitchen gardeners, and with thousands of them blanketing the area, it’s no wonder the Front Range is a hot place for psyllids to take their summer vacation.
These tiny tomato boogeymen have begun assaulting plants this season in what may be the vanguard of thousands of migrating psyllids (Bactericera cockereli). Dr. Whitney Cranshaw, Professor of Entomology at Colorado State University, has seen large numbers of these insects several parts of the state, including Larimer County. Sightings of the insect have also been reported in Longmont, Louisville and Boulder gardens.
The aphid-sized adults are lovely little things, with jewel-toned eyes and dark abdomens banded in white. Their young, yellow at hatching, gradually turn green with each molt; being flat and elliptical they look like scale. Though adults move about actively and fly in migration, the young are sedentary, content to sit quietly, feed, and excrete white, waxy frass that resembles sugar. This is their waste, called lerps, and is an easy to see clue that your plant is being attacked.
With their arrival in our area, gardeners are prepping for battle; these small, winged sap-feeding insects have toxic saliva that causes tomatoes and potatoes to grow oddly. Stunting, color changes, and strangely shaped fruit or spuds are a calling card of the insect.
Start scouting your plants, carefully checking them for insects or their signature sugar-like droppings every three days until you spot signs of trouble. Psyllids can mean big problems for tomatoes, so at the first sign of them begin spraying plants with spinosad or insecticidal soap to keep them at bay. Coverage of both upper and lower leaf surfaces is crucial to control, and may not be enough.
Several diseases show up in gardens at this time. Green plants turning blonde by yellowing from the lower leaves upward should be closely examined. If they have brown spots with concentric rings, suspect early blight (Alternaria solani).
Water, insects, and gardeners spread this fungus. Pick off diseased leaves and keep the ground free of debris. Dust healthy leaves with sulfur to shield them from infection. Once the plants have gotten three feet tall, pluck off leaves in the lower foot to prevent the spreading climb of the fungus. Give plants room to grow without crowding them, and use drip irrigation to prevent splashing water.
Black, sunken, rotten spots on the bottom of fruit are blossom end rot, a disorder caused by poor uptake of calcium. Though calcium is plentiful in our soil, irregular watering and excessive heat prevent the plant from using it. The key to control is watering consistently, so use a timer to automatically turn on and off the irrigation. Mulch plants to keep the soil from drying out too rapidly. Colorado State University Extension, together with Boulder County Parks and Open Space, provides unbiased, research-based information about consumer and family issues, horticulture, natural resources, agriculture and 4-H youth development. For more information contact Extension at the Boulder County Fairgrounds, 9595 Nelson Rd., Box B, Longmont, 303.678.6238, or visit the CSU Extension web site at