Utah Pests News Winter 2015

A New Disease of Potato and Other Solanecous Plants Reported in Utah

The non-culturable bacterium 'Candidatus Liberibacter solanacearum' is a pathogen that causes zebra chip disease of potato.  The bacterium is transmitted by potato psyllids (Bactericera cockerelli).  These insects are very small and look like black, winged aphids.  They have characteristic white bands on their backs that can be seen with a hand lens or dissecting microscope.  In the field, a hand lens is also required to see the eggs and nymphs.  The potato psyllids have been present in Utah for a long time, but the bacterium was detected for the first time in a potato sample in 2013, and again in 2014.

army cutworm caught in trap
Diseased pepper plants will have small, deformed fruit and pale yellow-green leaves.

The exterior of potato tubers affected with zebra chip appear perfectly healthy.  It is not until the tubers are sliced for cooking that the typical brown striations can be seen.  They are even more pronounced when fried, giving this disease its name.

Aboveground symptoms can be more noticeable.  Foliage will become chlorotic (yellow) and sometimes takes on a pink-reddish discoloration that could be mistaken for nutrient problems.  The reddish foliar discoloration is caused by a toxin produced by the potato psyllids.

In the last few years, this same bacterium has been found in tomatoes and peppers in New Zealand and in some states in the U.S.  In summer 2014, the disease was confirmed on commercial pepper plants from one field in northern Utah. 

army cutworm caught in trap
  Foliage of infected tomato plants will be chlorotic, especially toward the top of the plant.

Symptoms on peppers include stunted plants, small fruit, and pale yellow-green leaves.  On tomatoes, foliage can become deformed while the fruit may have a “strawberry” shape and the terminal growth will be chlorotic.  In some cases, interveinal chlorosis is observed.  Some of these symptoms are caused by potato psyllid feeding.

Control of the disease is through control of the potato psyllids early on in the season with application at planting of imidacloprid.  Later in the season, products containing abamectin can help.

I will be conducting a survey next summer.  If you have any suspicious plants, please contact me via email:  claudia.nischwitz@usu.edu.

-Claudia Nischwitz, Plant Pathologist

Featured Picture of the Quarter

featured pic

Females of the European wool carder bee (Anthidium manicatum) scrape or "card" fuzz from plants like lambs' ears (or even from wool socks or sweaters) for their nests, which are built in rotting wood or pre-existing tunnels.  Male carder bees are very territorial and will aggressively defend patches of flowering plants from other insects or pollinators, almost to the death.  This solitary bee has newly colonized Utah in the last 10 years, and in fact, now occurs throughout North America, North Africa, South America,  Asia, the Canary Islands, and New Zealand. 

-Image by Marion Murray, IPM Project Leader