Once the plants blossom, stop hilling up the soil, and apply a thick mulch to conserve moisture and keep down weeds. Water deeply during dry spells.
Climate and growing conditions can create a number of problems. Speckle leaf, a disorder that appears as dark splotches on leaves with sunken areas on the leaf undersides, is apparently caused by too much ozone in the atmosphere. Breeders are developing resistant cultivars. Keeping plants healthy and well cultivated is the best prevention.
Hollow areas in tuber centers are caused by rapid and uneven growth. To prevent this, plant seed potatoes closer together, cut down on watering and fertilizer, and avoid susceptible cultivars.
Other possible pests include blister beetles, leafhoppers, and wireworms. Blister beetles are ¾ inch long, slender, dark-colored insects that feed on leaves; reduce damage by hand picking (be sure to wear gloves to avoid blisters). Thin, wedge-shaped, ¼-inch-long leafhoppers cause 493leaves to curl and yellow; apply soap spray for control. Wireworms are ½- to ¾-inch-long larvae of the click beetle; these orange “worms” feed on and damage developing tubers. They are more prevalent in newly cultivated areas, so wait a few years after converting a lawn area into garden to plant potatoes there; crop rotation and frequent cultivation can also help.
An intriguing development in pest control is varieties such as ‘Prince Hairy’ and ‘King Harry.’ These varieties discourage leafhopper and Colorado potato beetles from feeding by virtue of their hairy leaves. The hairs contain sticky fluid that leaks out when hairs are touched, coating the insects with goo.
Avoid most potato diseases by rotating crops, providing good air circulation, keeping the garden clean, selecting resistant cultivars, and planting disease-free seed potatoes. If disease does strike, remove and destroy affected plants. Here are some diseases that might occur:
Blossoming plants are a sign that the first “new” potatoes are ready to harvest. Pull aside the earth around the base of plants and gently pick off cooking-sized tubers, which are delicious boiled with the skins on.
Once the foliage starts to wither and die back, the tubers will be fully grown. If the weather is not too warm or wet, they will keep in the ground for several weeks. Dig them up with a spading fork before the first frost. Potatoes that are nicked or bruised during harvesting won’t store well, so eat them as soon as you can. Clean and dry the crop as quickly as possible, but never expose it to sunlight. Store tubers in a dark place at around 40°F.
Note that potatoes with colored flesh often lose that color when cooked in water. To keep red and purple potatoes colorful, try roasting them instead of boiling.