The number of potato psyllids found in North Dakota and Minnesota continues to grow, albeit at a slow pace.

Between July 16-23, eight more psyllids were found in North Dakota and one more in Minnesota, according to a North Dakota State University pest report.

Since the initial finds in mid-June, a total of 21 have been found in North Dakota and five in Minnesota.

Potato psyllids can carry Candidatus liberibacter, which causes zebra chip.

Zebra chip, which is harmless to humans, causes the potato tubers to store sugars rather than starch.

When the potato is heated, such as during frying, the sugars caramelize, causing dark stripes.

Even in the absence of the bacteria, feeding by psyllids may cause leaf yellowing and poorly formed tubers, a problem known as psyllid yellows.