Leptinotarsa decemlineata This insect pest, also known as the potato bug, often devastates potato, tomato, eggplant, and pepper plantings. Both adults and larvae damage plants by devouring leaves and stems, damaging small plants most severely. The beetle was originally native to the Rocky Mountains and spread eastward in the late 1800s as potato plantings increased. It is now found in all states except California and Nevada. In some areas of the country, the beetle population may reach epidemic proportions. The beetles lay their yellow-orange eggs on the undersides of leaves as the first potatoes emerge from the ground in the spring. The larvae that hatch from these eggs feed for 2 to 3 weeks, pupate in the soil, and emerge 1 to 2 weeks later as adults, which lay more eggs. One generation is completed in a month. Depending on the area, there are one to three generations per year.

This plant disease is caused by a bacterium (Streptomyces scabies) that persists in the soil for long periods of time. Besides potatoes, scab also infects beets, carrots, and parsnips. The disease affects only the tubers, not the leaves or stems. Bacteria spend winter in the soil and in infected tubers left in the garden. Infection enters through wounds and through the breathing pores in tuber skins when the young tubers are growing rapidly. Scab is most severe in warm (75° to 85°F), dry soil with a pH of 5.7 to 8.0. The severity of scab often increases when the pH is raised with lime or wood ashes; it is not a problem in acid soils with a pH of 5.5 or less. Poorly fertilized soil also encourages scab. The bacteria withstand temperature and moisture extremes, even passing intact through the digestive tracts of animals-manure can spread the disease. Tubers infected with scab are edible, but much may be wasted as the blemishes are removed.

This plant disease is caused by a fungus (Alternaria solani) that attacks both vines and tubers. The same fungus causes early blight of tomatoes. It is most severe toward the end of the growing season when the vines approach maturity and after tubers are formed. Many leaves may be killed. The potato yield is reduced, but the plant seldom dies. Tubers are frequently infected through wounds inflicted during harvest. Early blight is favored by alternating periods of wet and dry weather and by temperatures from 65° to 85°F. The fungal spores spend the winter in plant debris left in the garden. Infected tubers are inedible.

These beetles jump like fleas but are not related to fleas. Both adult and immature flea beetles feed on a wide variety of garden vegetables, including potatoes. The immature beetle, a legless gray grub, injures plants by feeding on the roots and the lower surfaces of leaves. Adults chew holes in leaves, feeding for up to two months. Flea beetles damage young plants most. Adult beetles survive the winter in soil and garden debris. They emerge in early spring to feed on weeds until potatoes sprout. Grubs hatch from eggs laid in the soil and feed for 2 to 3 weeks, damaging the tubers. After pupating in the soil, they emerge as adults to repeat the cycle. One to four generations occur per year.

This plant disease is caused by a fungus (Phytophthora infestans) that seriously injures potatoes and tomatoes. The disease was responsible for the great potato famine in Ireland from 1845 to 1850 and is the most important disease of potatoes worldwide. The fungus spreads very rapidly, killing an entire planting in a few days. Infected tubers are inedible. Tubers are infected when spores wash off the leaves and into the soil, or they may be attacked during harvest and rot in storage. A soft rot often invades the damaged tubers. Late blight is prevalent in moist, humid weather with cool nights and warm days. Foggy, misty weather and heavy dew provide enough moisture for infection. Spores survive the winter in infected tubers in the garden or compost pile.

Empoasca fabae This insect feeds on potatoes and beans and on some fruit and ornamental trees. It sucks plant sap from the undersides of leaves, causing leaf stippling. This leafhopper is responsible for hopperburn and the browning and curling of the edges of potato leaves. The leafhopper injects toxic saliva into the nutrient-conducting tissue, interrupting the flow of food within the plant. Potato yields may be reduced drastically by hopperburn. Leafhoppers at all stages of maturity are active during the growing season. Both early and late varieties of potatoes are infested. Leafhoppers live year-round in the Gulf states and migrate northward on warm spring winds-even areas that have winters so cold that the eggs cannot survive may be infested.