KEYSTONE RUSSET

Prepared by Susie Thompson, Ph.D. and Robert D. Davidson, Ph.D., Department of Horticulture & Landscape Architecture, San Luis Valley Research Center, Colorado State University.

This profile was developed for production in the San Luis Valley. While some guidelines may be appropriate regardless of growing area, fine-tuning for specific production locales is recommended.

Keystone Russet is a very high yielding, medium russet-skinned, fresh market cultivar. Release is scheduled for 1999, by the Colorado and Idaho Agricultural Experiment Stations and the USDA. Keystone was tested as AC83064-1 and is the result of a cross between CalWhite (A76147-2) x A7875-5. It has low specific gravity and attractive tuber type. Plant variety protection is being pursued.

Plants/roots: Emergence is uniform, with a medium-sized, somewhat spreading vine and white flowers. It has a determinate growth habit and a moderate to shallow root system. Tuber initiation and bulking rate are medium.

Tubers: Tubers have white flesh, are oblong to long, with medium russet skin. Eyes are shallow and most prevalent on the bud end. Specific gravity is low (1.078).

Yield potential: Yield potential may exceed 500 cwt. per acre, with a high percentage of US No. 1 tubers produced.

GROWING SEASON MANAGEMENT

Pre-planting considerations: Tubers have a medium dormancy. Whole or cut seed is acceptable. Monitor size of seed, as sparse eye distribution on larger seed may result in "blind" seed pieces and stand problems. A seed spacing of 10 to 12 inches may optimize yield and desired tuber size for the commercial market. Plant this cultivar at about a 5-5.5 inch depth, which will reduce the potential for green tubers.

Fertility: Apply total fertilizer in the following range N(120-140#), P(80-190#), K (0-100#). Fertility needs are very minimal compared to other major russet cultivars. Pre-plant N applications should be in the range of 60-80#. Timing of tuberization is not affected by N applications. Spoon-feed remaining N at the rate of 7-10# per application (do not exceed 20# per application). Skin set may be difficult to achieve if nitrogen levels are high prior to vine desiccation. This may perpetuate skinning and tuber early blight problems in storage. Keystone's performance on alkali soils has been diminished.

Irrigation: Interval at the maximum ET is 3 days. Drought tolerance is moderate.

Pest Control

Weeds: Keystone Russet competes well with weeds. It is sensitive to metribuzin (Sencor, Lexone) applications.

Insects: Standard insect control measures generally are effective but timing and rotation of appropriate control is important due to high aphid preference and virus spread.

Fungicides: Begin application of appropriate fungicides for foliar early blight control when plants are 8 to 10 inches tall, and/or growing degree thresholds are met. This will result in 2 to 5 applications per season. Keystone is susceptible to late blight, thus if the pathogen is present, utilize an appropriately timed preventative program.

Tuberization/bulking: Keystone sets about 7 tubers per plant, and tubers are set in the middle of the hill. Tuber initiation and bulking rate are medium. Heat sprouts may occur when growing temperatures are high. Tubers are moderately resistant to blackspot bruise. Few internal or external defects have been noted during evaluation of this cultivar.

Vine Kill: Average days from planting to vine kill are 115 to 120. Vine killing is required, particularly if nitrogen applications have exceeded requirements. Adequate skin set occurs within 21 to 28 days.

STORAGE MANAGEMENT

Keystone Russet stores well with few problems, however, if tubers are immature or bruised during harvest and handling operations, Fusarium dry rot and early blight tuber decay may quickly become problems in storage.

DISEASE REACTION

Overall, disease problems are minimal. Bacterial ring rot foliar expression is adequate with typical symptoms and occurs within 90 days after planting.

Field

Foliar early blight Susceptible*

Verticillium wilt Unknown

Blackleg Susceptible

Seedpiece decay Susceptible

Leafroll virus Susceptible

Leafroll net necrosis Unknown

PVY Susceptible

PVX Susceptible

Common scab Unknown

Bacterial ring rot Susceptible

Storage

Tuber early blight Susceptible

Bacterial soft rot Susceptible

Fusarium dry rot Susceptible

Pythium leak Unknown

Pink rot (Phytophthora) Unknown

Silver scurf Unknown

Rhizoctonia scurf Unknown

*Disease reaction ratings = susceptible, moderately susceptible, moderate, moderately resistant and resistant.

12/99, revised 3/2000