While potatoes can be very easy to grow in most places, there are many diseases, pests and other issues that can arise. Identifying these problems is the first step to solving them. Not all conditions can be reversed and some plants may need to be destroyed, but catching the problem early can make all the difference. Pay close attention to the health and vigor of your potato plants and inspect them closely at the first signs of sickness. Here is a list of common problems when growing potatoes.
Early blight is a fungus characterized by dark brown spots that take over the leaves, eventually killing them. It is most common in warm, wet environments. Planting only certified resistant potato seeds helps reduce the risk of early blight. Mulching with hay also helps. Remove infected plants from the garden.
Late blight is a fungus that usually hits plants during cool, wet weather and spreads as temperatures rise. The leaves turn brown and then black and die. Severe outbreaks will kill the plant. Remove all infected plants from the garden.
Mosaic virus causes potato leaves to curl with shades of light green and dark green at the same time. Spread by aphids, most outbreaks won’t destroy plants but will reduce yields. Disease resistant potatoes can be sown to prevent mosaic virus. Keep aphids under control with insecticidal spray.
Potato Yellow Dwarf Virus
Transmitted by leafhoppers, potato yellow dwarf virus causes potato plants to dwarf. The leaves turn yellow and tubers may crack and disfigure. Diseased plants should be destroyed and not composted. Disease resistant varieties can be planted to eliminate the risk of this disease.
Common during wet growing seasons, potato blackleg causes leaves to turn pale green or yellow. The stems become dark brown and black just above the soil. The plants usually wilt and die. Tubers may be rotten upon harvest or rot in storage later on. Avoid planting potatoes in extremely wet conditions with poor drainage.
Potato scab is a soilborne bacterium. It causes scabby spots to appear on the tubers. Slightly acidic soil (4.8 – 5.2) helps reduce the risk of this disease. Resistant varieties are also available. Scab is usually just a cosmetic problem and tubers can still be harvested.
Bacterial Ring Rot
Bacterial ring rot causes potato leaves to yellow and curl upward. The tips may stunt. Stems may contain white ooze when cut and tubers contain yellow or light brown rot rings. Plants infected with ring rot should be discarded, tubers and all. Crop rotation and planting resistant varieties is the only good way to prevent this condition.
Colorado Potato Beetle
Adults are yellow with black stripes, a humped back and an orange head. The larvae are dark red or orange with black spots. They both feed on potato plant leaves and can devastate a crop. They should be picked off on site and sprayed if they start to become abundant. Try a basil and water mixture. Look for their orange egg clusters on the undersides of leaves. Companion planting potatoes with eggplant, flax and green beans can help prevent this bug.
Tiny, round holes found in potato leaves is likely a sign of flea beetles. They are brown or black and very small. More a danger to seedlings, adult potato plants can usually withstand flea beetles. Healthy, fast growers will be less susceptible. Good crop rotation and row covers when seedlings are young can help prevent them from making a home in your potato patch.
Yellowing, slightly curled leaves with tiny specks is usually a sign of aphid infestation. Aphids are tiny, oval insects that suck the life out of plant leaves and stems leaving a sticky residue called honeydew behind. They are usually pink or green and live on the undersides of the leaves. While most can be blasted off with water, you may need to use insecticidal soap if they get out of hand.
These are the larvae of the click beetle. They’re thin, brownish-yellow and about ½ – 1½ inches long. They may appear in areas that with fresh sod. They work in the soil and infest your potato tubers before they are ripe. If wireworms are a problem in your soil, you may need to grow potatoes in a pot as there’s not great way to get rid of them. Be sure to cultivate your soil deeply prior to planting, which can help disturb them if they are present.
Cutworms cut young seedlings off at soil level. They are gray grubs less than an inch long, live under the soil and attack at night. Mature plants are less susceptible. Protect seedlings with cardboard boarders until they grow large enough to fend for themselves. Oak leaf mulch, spread around the base of the plants, also helps.
Holes in your potato tubers may be a sign of slug damage. If harvested before the weather gets too wet, you should be able to avoid slug problems. Beer traps are also helpful if they appear before you’re ready to harvest.
Spider mites suck plant juice and cause the leaves to turn pale green, yellow or brown. They are usually accompanied by a silver, dusty web on the underside of the leaves and between the vines. Spider mites can usually be blasted off with water or sprayed with insecticidal soap. Ladybugs also feast on spider mites.
Psyllids are usually gray-green, brown or black. They are small, winged insects that inject toxin into the plant when they bite into it causing the leaves to curl up and turn yellow then brown. Young leaves may also have purple margins. Yellow sticky traps are good for catching psyllids.
Leafhoppers cause brown margins, white speckles and a scorched and wilted look. They are usually green, brown or yellow and about a third of an inch long. They have wedge-shaped wings and hop sideways from leaf to leaf sucking juice from potato plants and spreading disease. Young plants should be protected with row covers if leafhoppers are bad in your areas. Use insecticidal soap if they become a nuisance.
ENVIRONMENTAL STRESS & OTHER COMMON PROBLEMS
Too little moisture will cause leaf tips and margins to turn yellow and then brown and eventually die. Tubers may have brown spots in random places and grow in irregular shapes and sizes. Inconsistent watering during dry weather can also cause these symptoms. Water deeply, regularly and evenly throughout the growing season. Pay attention to long, hot, dry spells. Add mulch around your potato plants to help preserve soil moisture.
Too Much Water or Too Much Fertilizer
While deficiencies are a common problem growing potatoes, too much of a good thing can also be harmful. When potatoes grow to fast it may cause hollow tubers with cavities at the center. This is usually due to too much fertilizer and too much water. Potatoes should only be watered when the soil has dried to about 4 inches deep. Fertilize with compost tea or dilute commercial fertilizers before use.
Potatoes are commonly grown from pieces of mature tubers but they will not always sprout. Store-bought potatoes are usually treated with chemicals to prevent sprouting. Purchase organic or certified potatoes for planting. Be sure to plant a cutting that has at least two eyes and wait until the soil is 45° F or warmer.
If your plants are green and healthy but no tubers have developed, temperatures may be too warm. Potatoes need nighttime temperatures to be 55° F or cooler for tubers to form. In most areas, this mean they need to form in the cool of fall or before summer temperature get too hot.
If your tubers are green or become green after harvest they have likely been exposed to the sun. Sometimes there will just be green spots, caused by chlorophyll. Cut away the green parts of any affected tubers or discard the potato entirely. Potatoes should be grown under complete soil and stored in darkness.
Frost can cause young potato sprouts to stunt or die. They can also damage mature plants. Do not plant too early and harvest before the first frost in the fall.
Only plant certified potato tubers or seeds with at least two eyes to avoid disease and guarantee a good sprout.
Only plant potatoes in fertile soil. Getting a fast, healthy start to your potato plants is one of the most important preventative measures. Till deeply to disturb any pests that may be living in your garden. Add lots of mature compost to add nutrients and help with drainage.
Plant potatoes at the right time. Don’t plant too early or seedlings may be shocked and stunted and more vulnerable to pests and disease. Plant too late and tubers will mature when it’s too hot.
Water wisely. Too much or too little water can inhibit the growth of the potato plant and rot your roots and tubers. Use mulch to help maintain moisture in the soil. This will also help with pests. Avoid getting the foliage wet as this can foster fungal diseases.
Weed carefully. Good garden cultivation will help keep bugs at bay.
Handpick pests on site. Most bugs can be kept under control with some simple daily handpicking.
Harvest before tubers get over ripe and rot. For most areas this will be in September after nighttime temperatures have begun to drop.
Practice strict, smart crop rotation.
Keep your garden clean of debris, including dead leaves. A messy garden gives bugs a place to hide and disease places to breed.
Plant disease resistant varieties. Not all potatoes are created equal and this can really save you a headache in the long run.