In the Garden:
Southern California Coastal & Inland Valleys
November, 2007
Regional Report

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All those potatoes from just one; now that's magic!

Harvesting Your Very Own Potatoes

You cut the potatoes last May, making sure each piece had a couple of eyes. Then you snugged them into the soil or compost and watered them in. The sprouts may or may not have appeared, and then the plants either developed lushly, or they didn't. When you harvested your crop, they were either beautiful duplicates of the whole ones you'd chosen, or they weren't nearly as attractive. Now that you're considering your world of potatoes, you're wondering what happened. Here are some possibilities, and what to do next time around.

Problem: Potatoes that fail to emerge after being planted in cold wet soil may have rotted. If the potatoes were purchased at the grocery store, they may have been sprayed with a sprout retardant.
Solution: Plant certified seed when the soil has warmed. Incorporate compost to lighten the soil and provide better drainage.

Problem: Potato tuberworm eats tunnels in the tubers, and the shoots wilt and die.
Solution: Keep potato plants deeply hilled with soil. Don't allow soil to crack. Destroy infested vines and tubers.

Problem: Leafroll virus causes plants to be stunted and markedly yellow, and leaves to uniformly roll upward. Cut tubers have brown netting.
Solution: Plant only certified seed pieces. Spray peach trees for overwintering green peach aphid, which transmits the disease.

Problem: Stunted growth and leaves that turn yellow and brown between the veins and become brittle may be suffering from magnesium deficiency.
Solution: Incorporate dolomitic limestone or a handful of Epsom salts.

Problem: Rhizoctonia, also called black scurf, causes vines to suddenly wilt, stems to have brown lesions, and tubers to have irregular raised, black, hard bodies and be roughened in a cross-patched pattern. It is more prevalent in wet, cold, heavy, and poorly drained soil.
Solution: Plant clean certified seed of resistant varieties. Rotate the crop to a new area with cereal or corn crops on a five-year basis. Incorporate compost to lighten the soil and provide better drainage. Plant as late as possible in the season.

Problem: Tubers crack from sudden growth resulting from heavy irrigation after long drought conditions.
Solution: Water deeply and more frequently in dry weather.

Problem: Tubers are knobby-shaped or have cavities in their centers after undergoing alternately wet and dry conditions.
Solution: Irrigate more evenly. Incorporate compost to lighten the soil and maintain a more even moisture.

Problem: Tubers with corky scabs on the skin are likely to be infected with common scab that is most frequently a problem in dry, sandy, or gravelly soils that are alkaline and lacking in organic matter, and that have a high level of fresh manure.
Solution: Plant resistant varieties. Avoid using wood ashes, lime, or fresh manure. Incorporate compost to improve the soil texture and its ability to remain moist but not wet. Grow and turn under a green manure crop; the rapidly decaying matter will encourage beneficial organisms that compete with scab. Rotate crops on five-year basis.

Problem: Stored tubers become soft and rotten from infection that gained entrance through wounds inflicted during harvest and storage.
Solution: Be gentle with tubers during harvest and storage.


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