Answer: Common scab is most prevalent and severe in neutral (pH 7) or slightly alkaline soils. The optimum pH for scab development is from pH 6.0 to 7.5. In general, scab is not a serious problem in soils with a pH of 5.5 or lower. The scab organism is very sensitive to soil moisture, pH, and temperature. The incidence of the disease is generally greater in sandy or gravelly soils than in heavier soils. The amount of soil moisture at the time of tuber development is very important.
Several practices can limit the severity of scab.
1. Planting resistant varieties is the most feasible and practical control. Varieties showing some level of scab tolerance include: Norchip, Norgold Russet, Reliance, Russet Burbank, Shurchip, Norland, Hi-Plains, Pungo, Redskin, Russet Sebago, Shoshoni, and Superior.
2. Avoid planting seed exhibiting scab lesions.
3. Crop rotation in which potatoes will be planted in the same area only once every 3 or 4 years. Avoid rotating with root crops; instead plant grains, grasses, or legumes.
4. Maintain good moisture levels in the soil while tubers are developing.
5. Avoid the use of fresh manure just preceding the potato crop.
6. Chemically treating seed pieces before planting with the fungicide Captan will effectively reduce seedborne scab inoculum.
You may want to avoid the problem altogether by planting your potatoes above ground. You can purchase "potato barrels", or simply create your own. Use a piece of chicken wire or hardware cloth to create cylinders about 3
feet tall and 2 feet in diameter. Loosen the soil underneath for good drainage, and set the cylinder in place. Place a layer of hay in the bottom of the cylinder, and add a few inches of soil. Then plant your seed potatoes, about 4 per cylinder. Cover with another few inches of soil. Once the potato stalks have grown 4-6", add a layer of hay, then more soil, to cover the stalks, leaving the top leaves showing. Continue in this fashion until you reach the top of the cylinder.
You can begin harvesting when the first flowers appear, for those small, thin-skinned "new potatoes". Or wait until just before the first frost for full-sized potatoes. To harvest, simply remove the chicken wire and the potatoes will be easy to find!
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