Many of the resources provided here are not aimed at organic producers, but they do contain valuable information about potato production. If you are in doubt about suggested practices, please contact your organic certifier for advice.
Organic Potato Production Guide – Cornell University Cooperative Extension (pdf)
Potato Production Systems (University of Idaho).
Potato variety descriptions
Selecting and handling seed potatoes
Selecting, Cutting and Handling Potato Seed – University of Maine Extension publication (pdf)
Seed Selection and Handling (Alberta Department of Agriculture and Rural Development)
Potato handling, cutting and sanitation (Oregon State University)
Pests and diseases affecting potatoes
Compendium of Potato Diseases. Edited by Walter R. Stevenson, Rosemary Loria, Gary D. Franc, D. P. Weingartner. Available through APS Press and Amazon. This is a comprehensive guide to potato diseases and disorders, containing detailed descriptions and color photographs to aid in disease identification.
Common scab – caused by a soil bacterium, Streptomyces scabies. Scabby lesions on tuber surface. Lesions may be deep (“pitted scab”) or superficial (“russet scab”). Some potato varieties have moderate to good resistance to common scab. Common scab can affect root crops such as beets and carrots, so consider this when planning rotations. Consistent soil moisture, a soil pH at or below 5.2, and planting clean seed assist in controlling common scab. Fact sheet (Cornell University).
Silver scurf – caused by a soil-dwelling fungus, Helminthosporium solani. Grey lesions on tuber surface appear silvery when wet. Lesions can increase in storage, and spores can spread to other stored tubers. There is little to no resistance to silver scurf in cultivated potato varieties. Harvest tubers soon after skin set, since the fungus will grow and produce lesions on tubers as long as they remain in the soil. Use clean seed, practice crop rotation, and control volunteer potatoes to reduce silver scurf inoculum in fields. Fact sheet (Cornell University).
Black scurf – caused by a soil-dwelling fungus, Rhizoctonia solani. Black raised masses (sclerotia) on tuber surface – “the dirt that won’t wash off”. Underground sprouts and stolons are attacked and can be girdled and killed. Plant clean seed into warm soil, and practice crop rotation. Harvest tubers soon after skin set, since sclerotia form as vines begin to senesce. Fact sheet (Cornell University).
Early blight – caused by a fungal pathogen, Alternaria solani. Early blight infects tomatoes, potatoes, and other nightshades. Spreading lesions on leaves have a ‘target-spot’ appearance due to faint concentric rings. Spores are wind-dispersed, and can be deposited from infected vines onto tubers at harvest. Externally, tuber infections are small, irregular and sunken lesions, and internal lesions are discolored, firm and corky. Some potato varieties have moderate resistance to early blight. To control early blight, practice crop rotation, plant disease-free seed, orient rows to lessen canopy moisture, and dig tubers when vines are dry, not wet. Copper-based fungicides are quite effective against early blight, and several formulations are acceptable in organic production. Fact sheet (Cornell University).
Late blight – caused by an oomycete (water mold) pathogen, Phytophthora infestans. Late blight infects tomatoes, potatoes and other nightshades. Spores are spread aerially and by water splash, and lesions develop on leaves, stems and fruits. Tuber infection can occur when spores are washed into soil. Disease development is favored by moderate temperatures and wet conditions, and disease progress can be very rapid. Some tomato and potato varieties have resistance to late blight. Plant disease-free seed, orient rows to reduce canopy moisture, and scout the crop for disease symptoms. Copper-based fungicides are quite effective against early blight, and several formulations are acceptable in organic production. Fact sheet (Cornell University).
Colorado potato beetles (Leptinotarsa decemlineata) are voracious consumers of potato foliage as larvae and adults. The black-and-yellow striped beetles overwinter in the soil as adults, and will travel ¼ to ½ miles to potato fields when they emerge in spring. Females lay clusters of bright yellow-orange eggs on the undersides of leaves. Larvae have black heads, and are brick red when newly hatched and orange when older. Larvae have two rows of dark spots on their sides. Fourth instar larvae burrow into the soil to pupate. In the Midwest, Colorado potato beetles generally complete two generations per season. Physical control of eggs, larvae and adults can be quite effective for small fields. Some growers pull a child’s sled between rows and beat vines so that larvae drop into the sled. Mulching with straw can also reduce beetle numbers. Spinosad, a bacterial toxin, is effective for control of larvae, and is available in an organic formulation as Entrust. Note that spinosad is toxic to bees and other beneficial insects. Useful websites: Colorado Potato Beetle: Organic Control Options (ATTRA); Colorado Potato Beetles in Home Gardens (University of Minnesota Extension).
Potato leafhoppers (Empoasca fabae) cause damage to potatoes and other crops as they feed. The small yellow nymphs and bright green adults pierce cells and disrupt plant vascular tissue, leading to symptoms known as ‘hopperburn’ – browning or bronzing of leaves, followed by death of leaf margins. Some potato varieties show resistance or tolerance to leafhoppers. Natural enemies including predatory insects and fungal pathogens may provide some control. Pyganic, an organic formulation of pyrethrum, provides some control of potato leafhoppers when applied correctly. Useful websites: Potato Leafhopper on Vegetables (Penn State); Potato Leafhopper Garden Facts (pdf).