How to Manage Pests
UC Pest Management Guidelines
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 does possess 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. They are usually 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.
Psyllids used to be an occasional problem 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 in parts of southern California. Potato psyllid now occurs on a yearly basis in these areas and has become a chronic problem.
Damage is caused by a toxin that the immatures produce when they feed. The toxin causes a plant response known as 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, and the formation of aerial tubers. Internodes are shortened and the plant eventually is dwarfed and appears pyramid shaped. The nature of psyllid yellows is unlike a virus. (Do not confuse psyllid yellows with the symptoms of calico virus. Symptoms of calico virus are not uniformly distributed and leaf rosetting is not present.) 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.
Psyllids also vector an organism that is responsible for a condition known as zebra chip. The organism causes sugars to accumulate in areas of the tuber instead of starch; affected tubers have dark lines throughout the entire length. In chipping varieties, these areas turn black when the chips are fried, creating a black, striped effect that gives rise to the name "zebra chip". Infested plants produce fewer tubers. Yield losses from 20 to 50% have been reported. Tubers that are produced on plants attacked early in development will prematurely sprout in storage.
Use yellow sticky traps to detect the presence of potato psyllid and initiate leaf sampling. Currently leaf sampling methods and thresholds are still being developed for this pest. It is recommended that the undersides of leaves be examined for nymphal stages. Because potato psyllid nymphs can be difficult to see on a potato leaf, planting a few pepper or bean plants in the field can provide an easier way to detect the nymphs. Bean, and especially pepper, plants have smooth leaves and are readily infested by the psyllids, making it easier to detect them on these crops than on potato plants. Keep records of your sampling results (example form.
Potato fields in areas where the psyllid is known to occur should be treated at planting with imidacloprid. During the growing season, if monitoring indicates that populations are present and there is an average of 1 to 2 psyllids/leaf or 10/plant, additional treatment may be warranted.
UC IPM Pest Management Guidelines: Potato
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