Source: Michigan State University Extension
Volunteer potatoes are potato plants that emerge from potato tubers that were left in the field in the previous growing season. Many potatoes are left in the field after harvest simply because they are not picked up by the harvester or they are too small to make it up and through the harvester. More remain intermingled with stones that were collected by the harvesters and subsequently removed with the stones. Still more come from the disposal of cull potatoes that are removed on grading lines when potatoes are sorted at the warehouse or packing shed and are taken back to the field as a means of disposal.
When harvesting, a few potatoes are often spilled or left behind in the field.
If these tubers do not freeze over winter, they may survive to produce sprouts that become volunteer potato plants in the following season. They can be a difficult weed to control in many crops due to limited herbicide options and volunteer potatoes often emerge from the soil for extended periods of time through spring. They are an important weed to control, especially for potato growers. While like other weeds, volunteer potatoes sap nutrients and water from the crop they are growing in and also pose an additional threat—being a source of disease for a nearby potato crop.
Many diseases require live potato tissue to survive even for short periods of time, most notable among these are late blight Phytophthora infestans and potato virus Y (PVY). If these diseases are present, even at low levels in a growing crop, any volunteer potatoes that grow from that crop can carry that infection over winter. In spring as these volunteers grow they will likely not be receiving protective fungicide applications and they may already be harboring disease that can spread into the nearby potato crop.
Controlling volunteer potatoes
Potatoes left on the surface will likely freeze during the winter months.
To effectively control volunteer potatoes, begin efforts in the fall at harvest. Keep tubers on or near the soil surface in the fall to maximize tuber freezing. Avoid tillage that will bury tubers deep in the soil where they may not freeze toughly during winter. Avoid spreading large amounts of organic materials such as manure with livestock bedding on top of tubers in the fall and winter and manage crop residue and cover crops to minimize areas where tubers may survive freezing temperatures by being insulated.
Manage stone piles and disposal of cull potatoes. Pile stones that are removed from the field or the grading area to areas that are accessible and can be monitored for the emergence of volunteers next spring and summer. Cull potatoes that are spread on fields should be spread thinly on the surface where they will be exposed to freezing temperatures or composted.