Net necrosis is defined as tiny areas of dead cells found inside potato tubers. It is a general term used to describe a symptom. Net necrosis appears as slightly off-color specks or streaks in raw tubers. For instance, the areas appear slightly more white than the surrounding flesh or meat (inside of tuber) in white potatoes regardless of the skin color. These specks or streak areas appear brown when the tubers are sliced and fried thereby resulting discolored potato chips and fries. There are primarily three causes associated with net necrosis: chilling, potato leaf roll virus infection and, recently, zebra chip.
Chilling of tubers results from the potato tubers being exposed to near freezing temperatures but not so below freezing that the tubers undergo freeze damage. Net necrosis appears as specks scattered the portion of the tuber that has been exposed to the low temperature, and therefore, the specks occur from the skin inward, usually on one side of the tuber as normally the whole tuber would not be chilled. See Physiological Disorders / Internal Disorders / Chilling for details.
Infection of plants by Potato Leaf Roll Virus (PLRV) is the most common cause for net necrosis. The net necrosis normally appears in a star burst pattern eminating from the center of the tuber. This virus is seed-borne and is a major criteria for certifying seed potatoes. See Diseases / Viruses / Leaf Roll. Potato Leaf Roll Virus is spread from infected to plants to healthy plants by way of an insect vector, certain aphids. The most problematic of these aphids is the Green Peach Aphid. So, if there are infected plants growing from infected seed or infected weed hosts such as nightshades, PLRV will spread if the vector aphids are present. Control, then, involves treating the field with an appropriate insecticide. This is especially important in seed production fields where extra care is needed. See Insects / Vectors / Green Peach Aphid.
Infection with the Zebra Chip - causing pathogenic agent will cause a distinctive net necrosis. The net necrosis resulting from zebra chip, and which gives the disease its name, appears either as specks or streaks throughout the potato tuber. See Diseases / Tuber Blemishes / Zebra Chip. Much is still not known about the causal agent(s) of zebra chip nor of how it is carried and spread. A roll of potato psyllids in its spread has begun to be verified. See Insects / Vectors / Potato Psyllids.