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Jeff Green | May 28, 2009

by Helen Halpenny, Lanark County Master Gardeners

Potato varieties are classified as early maturing, such as Superior, and Eramosa, or late maturing, such as Russet Burbank, Chieftan, and Kennebec. Yukon Gold is yellow–fleshed, and Caribe is blue. Banana is a gourmet favorite fingerling. The choices are numerous.

After you have planted your sets there will be a few weeks until the sprouts appear above ground. Soon thereafter you may encounter the Colorado Potato Beetle. The adult beetles, which are striped yellow and black and about 10mm long, over winter in the soil and when the soil warms, they emerge and seek host plants such as potatoes, tomatoes, and eggplant. The females lay orange egg masses on the undersides of the leaves. If you can locate these egg masses and squish them before they hatch and start feeding on the potato leaves you will control them. The hatched larvae are brick red with rows of black dots. They feed continuously and can defoliate a plant in short order. I take a bucket and a shingle to the potato patch and tap the plant branches, knocking the little beetles into the bucket. They are then given a boiling water bath.

Another problem with potatoes can be late blight. This may happen under wet, cool conditions during late August and September. It is usually worse on low-lying, wetland and heavier soil. Brownish black blotches on the lower leaves are the first symptoms. If late blight has infected the foliage in late summer, cut the stems at ground level and wait two weeks before digging. If dug right away, the tubers become infected by the fungus spores on the ground or freshly cut foliage and many will rot in storage.

Common scab is a disease caused by soil dwelling, bacteria-like organisms. Roughened, discoloured patches occur on the surface of the potato tubers. Avoid fresh manure applications, and alkaline soil. Always plant certified seed. Changing the location of your potato patch each year is helpful, too.

Potato crops need adequate moisture during the growing season. When the little potatoes start forming, the plants demand good amounts of nitrogen, phosphorus and potassium. Irregular watering disrupts the normal growth process. Knobby, misshapen potatoes or hollow hearts can result.

Potatoes need to be weeded at least once to let them compete for moisture and nutrients. If they are planted in the ground, they will need to be ‘hilled up’ to ensure that the developing tubers are covered by soil to exclude the sunlight.

New potatoes can be dug anytime, but storage potatoes should be left in the ground for at least two weeks after the tops have died down. This underground rest toughens the skins and allows the potatoes to convert sugars into starches, making them better for baking and frying. A garden fork is the best potato-digging tool. Try not to spear the tubers. Any injured tubers should be used right away. Leave the tubers outdoors for several hours to dry off. They must be stored in a cool, moist environment away from light.

For gardening information call Renai Rennick at 613-267-7272.

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