Technical Information Bulletin 5: Roguing Potatoes

Roguing is a critical factor in potato production, as systemic infections, especially those caused by viruses, can establish a serious disease cycle, leading to complete degeneration of formerly healthy seed. Diseased plants can spread disease to healthy plants through insect vectors or mechanical contact. If the disease is not controlled, a nearby potato crop can become completely infected within a few years. Systemic infections within the potato plant move easily into the potato tubers. When infected tubers are used as seed, the resulting plant also becomes infected, establishing a serious disease cycle. Control components to break this disease cycle include reducing insect vectors, such as aphids, by proper caution in leaf and stem management, and roguing. The type of plants to be rogued fall into three categories: diseased plants, atypical plants, and volunteer plants. Diseased plants exhibit symptoms such as systemic viral, bacterial, and fungal infections, which can lead to leaf deformations and atypical plant growth. Atypical plants are those that do not conform to the variety's characteristics, such as flowering, stem shape, and color. Volunteer plants are those that remain in the field from previous seasons and are not part of the planted variety. To be effective, roguing should begin immediately after infected or undesirable plants are detected, usually a few days after emergence. The sooner the infected plants are removed, the less chance there is of disease being spread to healthy plants. Roguing consists of four basic steps: identifying plants to be rogued, digging up plants, removing plants from the field, and destroying plants. When identifying plants to be rogued, familiarize yourself with the characteristics that a variety displays under your particular field conditions. Stay at least one row away to compare differences within groups of three to five plants. Once you detect differences, move closer to verify the specific symptoms. Also, avoid changing the staff responsible for roguing, as individuals who frequently check the fields will not easily notice subtle changes in a plant. Once a plant is infected, the disease spreads to all its vegetative parts. Therefore, all parts of the plant should be removed, including the smallest tubers and stolons, as well as the mother tuber. If not, rogue shoots from these plant parts may become a new source of infection. Use a fork when digging up the plant, do not remove the plant by hand, as parts may break off and remain in the soil. To avoid disseminating infective (virulent) plants, place rogue plants in aphid-proof bags to be removed from the field. This prevents aphid vectors from reinfesting the crop. Destroy plants by burning or burying infected plants. Crop uniformity is a critical factor in roguing. Uniform crops are easier to roguing, while irregular-growing crops make it difficult. To achieve a uniform crop, group the tubers and plant them in a uniform pattern. Certain factors, such as crop density and soil conditions, can also affect roguing.