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The Garden Plot for May 16, 2008
3:55 PM - 4:00 PM
[Program Website]
Today's Highlight: “Potatoes”
Our average last spring frost date is May 25th to June 4th, so now is a good time to plant potatoes. Potato foliage is susceptible to freeze injury, but you can plant tubers a few weeks prior to the last frost date since it takes time for tubers to sprout and form leaves.
Potatoes are heavy feeders and require a loose, fertile soil amended with high nitrogen and phosphorus fertilizer. They do best planted in raised beds or hills with drip irrigation. Sprinkler irrigation encourages fungal leaf diseases, such as early blight. Because potatoes are shallow rooting, they are prone to drought stress. Keep potatoes well and evenly irrigated to avoid disease and misshapen potatoes at harvest.
The biggest problem potatoes have in Montana is a disease called scab. Potato scab causes tuber surfaces to develop brown, roughened, raised or pitted, and warty-looking areas.
Potato scab bacteria survives in the soil; it can attack the roots of weeds and other root crops. The bacteria is inhibited at a soil pH higher than 7.4 and lower than 6.0. Optimum soil pH for scab is 7.0. The bacteria invades when potato tubers are developing during the first 5 weeks after planting. If potato tubers dry out during this period, they are much more susceptible to scab.
Be careful not to let potato soil dry out during early tuber development. Good moisture from one week before first shoots emerge until eight weeks after emergence can greatly reduce scab severity. Research has shown that the microorganisms surrounding potato tubers are antagonistic to the scab bacterium under high, but NOT under low, soil moisture conditions. Mulching with straw (as long as your soil has good drainage) may help to maintain higher moisture levels and discourage scab. Resistant cultivars include: 'Superior', 'Russet Burbank', 'Pungo', 'Rhinered', 'Onoway', 'Russian Banana', 'Beltville', 'Norland' and ‘Dark Red Norland’. Other red scab resistant cultivars include ‘Chieftan’, ‘French Fingerling,’‘La Rouge’, ‘Red Cloud’, ‘Reddale’, and ‘Rose Finn’. ‘Purple Viking’ has purple skin color and excellent scab resistance. Unfortunately, most of the red and purple fleshed potato cultivars are only moderately resistant to potato scab. ‘All Red’ and ‘Huckleberry’ are red-skinned cultivars with pinkish-red flesh and good potato scab resistance.
For more information on growing potatoes and potato scab resistant cultivars, contact your local county extension office.
Helen Atthowe's new short program of gardening tips
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