Potato Psyllid

Potato psyllids look like small cicadas, about 0.08 inch (2 mm) long. They are related to aphids and leafhoppers. The adult has clear wings that rest rooflike over the body. Although predominantly black, the potato psyllid possesses white markings. The first abdominal segment shows a broad white band, the last segment has an inverted white "V". Psyllids jump quite readily when disturbed.

The football-shaped eggs are extremely small, slightly larger than leaf hairs, and on a short stalk. Although they can be found all over the leaves, they are easiest to see on the underside of the leaf along the edge and in the upper plant canopy. A 10X hand lens is required to see them.

Psyllid nymphs look like immature soft scale or whiteflies. Unlike whiteflies, when disturbed, they move quite readily. They are flat and green with a fringe of short spines around the edge. The immatures go through five instars in as little as 13 days depending on temperature.

Psyllids used to be an occasional problem on potatoes, peppers, tomatoes, and other solanaceous crops in California in certain years when they would migrate into the state from Mexico. In recent years however, a more invasive form of the species has been found in California that has the ability to overwinter. Potato psyllid now occurs on a yearly basis and has become a chronic problem for potatoes.

Potato psyllid can cause the damage to the crop in more than one way. Psyllids transmit a bacterium Candidatus Liberibacter solanacearum (LSO) which is responsible for a condition known as zebra chip. This disease severally affects potato plant growth and yield. The bacterium causes sugars to accumulate in areas of the tuber instead of starch. These areas turn black and more pronounced when infected tubers are processed into fried chips or fries, creating a characteristic pattern that gives rise to the name "zebra chip" and makes potato chips and French fries unmarketable. Whole crops might be rejected, leading to abandonment of entire fields.

While zebra chip is the characteristic symptom of an infection with the LSO bacterium, other above ground symptoms can include aerial tuber formation, plant stunting, and chlorosis resembling psyllid yellows diseases. Infection is irreversible, and symptoms continue to increase in severity over the time. Potato plants affected by the disease early in the development can die in less than 3 weeks. Plants exposed to LSO-infected psyllids less than three weeks before harvest usually produce tubers without zebra chip symptoms. It is not known how extensively or how rapidly symptomless but infected tubers develop zebra chips symptoms in storage.

Feeding by potato psyllid nymphs, and sometimes adults, can also result in psyllid yellows. Symptoms include an upward curling of leaflets nearest the stem on the top part of the plant. As the disease establishes itself, this symptom becomes more evident. Plant yellowing is the most common symptom. The yellowing (in some varieties, purpling) is initially found on the leaf edges. Severe symptoms include overall yellowing with enlarged nodes, development of clusters of small leaves in the axillary buds that appear rosetted. Internodes are shortened, and the plant eventually is dwarfed and appears pyramid shaped. Below-ground symptoms include setting of excessive numbers of tiny misshaped potato tubers, production of chain tubers, and early breaking of tuber dormancy If the immature psyllids are removed from the plant, the progression of the disease will stop. As few as three or four nymphs per plant can produce symptoms but more are needed for severe symptoms.  Psyllid yellows is suspected to be caused by a currently unidentified toxin that immature psyllids produce when they feed.

Third, feeding by potato psyllids results in substantial honeydew accumulation and can lead to fungal infestations.

While various predators and parasites including spiders, lacewings, and the parasitoid Tamarixia triozae, may attack psyllids, most parasites attack too late in the psyllid life cycle to stop crop loss. However, conservation of existing natural enemies, especially predators, provides additional control and therefore it is critical to use pesticides that maximize the effects on the psyllids while minimizing the effects on natural enemies.

Use sprays of the Entrust formulation of spinosad on an organically certified crop.

It is increasingly important that management of the potato psyllid take an area-wide approach that considers all potential host crops, particularly tomatoes. Psyllid movement between crops, timing of crop planting, and which crops are adjacent to others all need to be considered.

Use yellow sticky traps placed at the field margins near the tops of plants early in the season to detect the movement of the first potato psyllids invading the crop. If psyllids are caught in the traps, examine foliage of potato plants. Because potatoes are highly susceptible to the zebra chip pathogen, sampling must consider all life-stages. Nymphs are most easily identified and occur in greater numbers than adults in California. Plants should be sampled from multiple locations in the field. However, the field margins are a good place to start sampling because these insects colonize the edges of fields first. Very early in the season, examine whole plants; later concentrate on leaves in the top two-thirds of the plant. Nymphs and eggs are typically located on the underside of leaves. Sample and examine with field hand lens 12 to 50 plants, with 20 being optimal. Inverted lead blowers can be used for adult sampling. Keep records of your sampling results (example form—PDF).

In southern states (e.g. Texas), where potato psyllids are known to affect potato plants since plant emergence, it is recommended that potato and tomato fields in areas where the psyllid is known to occur should be treated at planting with neonicotinoid insecticides, such as imidacloprid. Be aware that at some locations potato psyllid appears to have developed resistance to imidacloprid. There are no reports of resistance to imidacloprid in California or the Pacific Northwest. In the Pacific Northwest insecticides at planting are not recommended for psyllids control since psyllids arrive in potato fields late June, early July.

Currently, there is no economic threshold for psyllid in any North American crop, including potatoes. Most growers treat immediately when first potato psyllids are detected in the field due to the risk of zebra chip. Do not let a generation complete its life cycle in the field and reproduce, as the LSO pathogen will spread rapidly with the help of its psyllid vector. Rotate insecticides with different mode of action to minimize resistance development.

If psyllids are present in the field, it is very important not to use carbamates (e.g., Sevin-foliar applications, Lannate, Vydate) for the control of other pests as these materials actually promote the increase of psyllid numbers.

• Surveying foliage pests form (PDF).