It is potato season in Idaho and plants are at the stage prone to invasion by a tiny insect known as the potato psyllid, scientifically identified as Bactericera cockerelli. Indeed, reports show that, as of this writing in mid-June, the tiny beast is already sneaking in this year!
WHAT IS A POTATO PSYLLID?
Potato psyllids are sap-feeding insects related to aphids and leafhoppers. Adult potato psyllids are about the size of an aphid, with transparent wings and a dark body that is shaped like a miniature cicada. There are distinct white markings visible on dorsal side of the abdomen. In addition to wing characteristics, markings on the head and abdomen are used to identify the species. Eggs are oval-shaped and orange in color and placed at the end of a short stalk.
Immature psyllids go through five nymphal stages before they molt into the adult stage. Nymphs are yellowish green in color and can be found on both sides of the leaf and on the stem of the infested plant.
WHY SHOULD WE BE CONCERNED ABOUT POTATO PSYLLID PRESENCE?
It has been known for decades that potato psyllids can inflict direct damage by feeding on foliage of a wide range of cultivated and wild solanaceous plants.
Prominent examples of vegetable hosts include potatoes, peppers, eggplants and tomatoes. Yellowing, leaf curling, shortened internodes and aerial tubers are some of the damages caused by direct feeding. However, potato psyllid association with zebra chip disease of potatoes has become a major concern in recent years. Zebra chip is a condition caused by a bacterial pathogen (Candidatus Liberibacter solanacearum, Lso), that is transmitted by the potato psyllid. In addition to the above-mentioned foliar symptoms, the infected potato tubers show brown stripes when sliced and fried. In the U.S., the disease was first discovered in Texas in 2000. Since then, it has been detected in several other potato-producing states. In 2011, the disease was reported in the Pacific Northwest, a region that accounts for more than half of all U.S. potato production.
It is generally believed that potato psyllid populations start to build up in warmer regions such as northern Mexico and southern Texas earlier in the season; increased temperatures in overwintering/ breeding sites trigger their northward movement, which can extend as far as the Canadian border. However, in addition to reports on cold tolerance of potato psyllids, the presence of overwintering populations in the Pacific Northwest region has triggered further investigations on psyllid movement patterns, the presence of local overwintering populations, and potential associations between local populations and zebra chip incidence.
To date, insecticide application has been the only way to minimize Lso spread by suppressing psyllid numbers. For the past several years, national and statewide monitoring programs have been in place to track and report psyllid presence across potato growing regions of the U.S. to assist scheduling chemical applications. Due to the wide host range of the psyllids, some monitoring efforts have been extended to natural vegetation in and around production areas to determine potential pathogen/ insect reservoirs in the absence of a potato crop. Monitoring efforts, however, can also benefit from help from local communities, small-scale producers, and even individual home gardeners. Inspecting garden plants and plants obtained from local nurseries would be an important step to identify and subsequently limit potential sources of vector and pathogen spread across production areas.
More information on potato psyllids and zebra chip can be found in a paper published by J. Munyaneza in the 2012 American Journal of Potato Research.
Becoming a member of the Potato Association of America gains interested parties free access to that article and others.