Checklist of Potato Emergence Problems

This bacterium is found in all agricultural soils and in surface water. Soft rot is favored by free water and high temperatures.

Soft rot bacteria are present in tuber lenticels and penetrate tubers through wounds or bruises. Fusarium infection of seed can predispose seed to bacterial decay. This can happen when seed potatoes are left in a truck on warm days for 24 hours or longer or planted in warm and wet soil.

Rotted tissue is brown, mushy, slimy, water soaked and surrounded by a black margin. Infected seed often has a foul odor and seed rots quickly in the field, leaving gaps in rows.

Photo Credit:

Eugenia Banks, Ontario Potato Board

Tuber soft rot.

This pathogen is primarily seed borne. Rot starts at the stem end and extends into the tuber. Infected flesh first appears cream-colored but turns darker, grayish black and mushy with time.

Secondary bacteria that invade affected tubers give off a fishy smell. Planting infected tubers may result in seed rot and pre-emergence or postemergence stem rot called blackleg.

Photo Credit:

Eugenia Banks, Ontario Potato Board

Blackleg of potato seed tubers.

Photo Credit:

Andy Robinson, NDSU/University of Minnesota

Potato stem blackleg.

The symptoms of Dickeya tuber rot are very similar to blackleg; however, Dickeya tuber rot often looks “cheesy” and it is usually not as smelly as blackleg. Healthy-looking seed tubers may carry the Dickeya bacterium in a dormant state; such tubers usually rot and plants wilt when spring temperatures are close to 77 F (25 C.)

Photo Credit:

Eugenia Banks, Ontario Potato Board

Dickeya in seed tuber.

Tuber infection occurs at wound sites. External tuber lesions are sunken and shriveled with concentric wrinkles. Rotting flesh may be brown or gray to black, dry and crumbly.

Cracks often form in the lesions and cavities often are lined with white, pink, yellow or blue mold that develops on the rotted tissue. Infected seed pieces may be partially or completely destroyed in the soil, resulting in uneven stands.

Photo Credit:

Eugenia Banks, Ontario Potato Board

Fusarium seed piece decay in tubers.

External tuber lesions are slightly sunken brown to purplish areas of variable size. The internal symptom is a tan to brown granular dry rot. No clear separation occurs between infected and healthy tissue.

Often, soft rot bacteria invade infected tubers. Infected seed may rot in the field or weak, sick plants may emerge. Later, lesions that develop on these plants produce thousands of spores that can start an epidemic if the weather is cool and wet.

Photo Credit:

Eugenia Banks, Ontario Potato Board

Late blight seed infection.

This fungus produces light brown blemishes with microsclerotia on the tuber skin. Later, unsightly dark brown patches can develop.

Lesions tend to be irregularly shaped and often without a defined outline. The black dots (microsclerotia), which differentiate this disease from silver scurf, are easily seen under a hand lens (10x magnification).

In very susceptible varieties, the lesions are black and cover larger areas of the tuber. Eyes within affected areas produce weak sprouts, resulting in poor stands if severely infected seed is planted.

Photo Credit:

Eugenia Banks, Ontario Potato Board

Black dot infection on seed tubers.

Photo Credit:

Eugenia Banks, Ontario Potato Board

Black dot infection in seed tubers.

A symptom of this disease is the formation of brown cankers on sprouts. Brown cankers may pinch off sprouts, resulting in poor emergence.

Photo Credit:

Steve Johnson, University of Maine Cooperative Extension

Rhizoctonia on sprouts.

Photo Credit:

Andy Robinson, NDSU/University of Minnesota

Rhizoctonia on stem.

This is most often seen in potato virus Y (PVY)-infected plants that emerge and die prematurely, which results in poor stands. Infected plants exhibit a necrotic leaf drop symptom of lower leaves.

Photo Credit:

Eugenia Banks, Ontario Potato Board

PVY-infected plant.

Tubers infected by C. Liberibacter solanacearum, the cause of zebra chip, do not sprout or sprout with hair sprouts.

Photo Credit:

Gary Secor, NDSU

Tubers infected by C. Liberibacter solanacearum.

This can occur by tuber exposure to temperatures between 31 and 34 F (minus 0.5 to 1.1 C). This may occur while the crop is still in the ground before harvest, in transit or in storage.

Chilling injury is not visible on the tuber surface but causes pinkish-red to reddish-brown or gray discoloration of the flesh. (The reddish-brown discoloration symptom is called mahogany browning).

The vascular tissue is very sensitive to chilling injury. Chilled cells are not frozen, and tissues do not break down rapidly. Chilled potatoes should not be used for seed.

Cut surfaces do not heal properly, and seed-piece decay is likely. Sprouts from chilled potatoes usually die off.

Photo Credit:

Eugenia Banks, Ontario Potato Board

Chilling injury to tuber.

Soil temperatures below 28 F (minus 2 C) for several hours kill the tuber tissue closer to the soil surface. Symptoms become visible as the tubers begin to thaw, resulting in free moisture (weeping) on the tuber surface.

Later, cellular breakdown causes the tissue to turn brown, gray or black. A distinct line is visible between healthy and frozen tissue.

Photo Credit:

Troy Fishler, University of Wisconsin

Freezing injury on part of tuber.

Photo Credit:

John Nordgaard, Black Gold Farms

Freezing injury effects on tuber.

Photo Credit:

John Nordgaard, Black Gold Farms

Freezing injury.

Freezing temperatures kill emerging sprouts. New sprouts regrow from healthy tissue, emerging at a 90-degree angle to the stem. This delays emergence for at least a week and the stand is not uniform.

Photo Credit:

Eugenia Banks, Ontario Potato Board

Frozen sprout damage.

Photo Credit:

John Nordgaard, Black Gold Farms

Frozen sprout damage.

Pressure bruising in storage or bruising seed potatoes before planting increases seed piece decay by providing entry points for bacteria or pathogens such as bacterial soft rots and Fusarium spp. or may reduce sprouting due to eye damage.

Photo Credit:

Andy Robinson, NDSU/University of Minnesota

Pressure bruise.

Seed that accumulated many growing degree days or was stressed in the field prior to harvest, was not properly stored or was stressed by excessive handling can produce recognizable symptoms. It has sprouts, or second growth, and/or it can be spongy or dehydrated.

Planting seed with these symptoms can result in missing plants, slow emergence, multiple stems and a nonuniform stand in the field. In the field, hot soil temperature is the main cause of seed aging.

• Little potato disorder or no top: New tubers are produced directly from the sprouts, without emergence. (Figure 13a)
• Hair sprouts: High soil temperature toward the end of the growing season causes this disorder. Hair sprout disorder may develop on physiologically old tubers along with the formation of little potatoes resulting in poor stands. Hair sprouting is also a symptom of infection with the black dot fungus. (Figure 13b).

Photo Credit:

Andy Robinson, NDSU/University of Minnesota

Little potato tuber disorder or no top.

Photo Credit:

Steve Johnson, University of Maine Cooperative Extension

Hair sprouts.

This can occur during tuber development and/or storage by the lack of oxygen, leading to dark, necrotic cavities. Increased temperature can intensify blackheart, especially after vine kill and when soils are saturated. Seed with severe blackheart disorder often rots before emergence.

Photo Credit:

John Nordgaard, Black Gold Farms

Blackheart of potato tuber.

• Chlorpropham (CIPC) contamination in storage: The sprouts of seed contaminated by residues of CIPC in storages are cauliflower-shaped and will not produce plants.
• Maleic Hydrazide (MH-30) residues in seed from contact during previous growing season: MH-30 suppresses sprouting, and suppression of emergence depends on the residue level and size of the tubers. The larger the tubers, the higher the concentration of residues. Residues decline with time and sprout development occurs, but growth is substantially delayed.
• If accumulated in sufficient quantities, sprout-inhibiting compounds may cause delayed emergence of seed tubers.

Sprouts inhibited by CIPC.

Herbicide carryover in soil: Patterns of soil carryover will have consistent injury symptoms in the areas of the field or where the herbicide carryover is a problem. Issues can be in the entire field or specific areas with higher herbicide carryover based on soil characteristics or previous herbicide application.

Photo Credit:

Andy Robinson, NDSU/University of Minnesota

Herbicide carryover in soil.

Photo Credit:

Andy Robinson, NDSU/University of Minnesota

Disrupted plant growth caused by herbicide carryover in soil.

Herbicide residue in seed: Seed may not sprout or have cauliflowerlike sprouts and/or candelabralike stems caused by herbicides, causing a loss of apical dominance. That is most commonly caused by glyphosate.

Emergence most often will appear as scattered injury throughout the seed lot. Some plants will look normal; others will show varying levels of herbicide injury symptoms.

Photo Credit:

Andy Robinson, NDSU/University of Minnesota

Erratic stand from glyphosate residue in seed.

Photo Credit:

Andy Robinson, NDSU/University of Minnesota

Multiple sprouts from glyphosate residue in seed.

Herbicide damage by soil type: Soils with low organic matter and high pH can cause herbicides to be more active and increase injury symptoms. Some varieties are more susceptible to herbicides such as metribuzin.

Photo Credit:

Andy Robinson, NDSU/University of Minnesota

Metribuzin damage to CalWhite potato plant.

Chloroacetamide herbicide injury: Cool and wet conditions will increase plant uptake and prolong plant metabolism, causing slow growth and malformed leaves. The active ingredients metolachlor and dimethenamid can cause slowed emergence.

Photo Credit:

Andy Robinson, NDSU/University of Minnesota

Chloroacetamide herbicide injury.

This refers to tubers with eyes concentrated at the bud end (e.g. ‘Ambra’) or that have a low number of eyes (e.g. ‘Bannock Russet’). This results in blind seed pieces when the seed is cut. Blind seed pieces will not sprout, resulting in poor emergence.

Photo Credit:

Steve Johnson, University of Maine Cooperative Extension

Eyes concentrated at bud end.

Varieties with low dry matter such as ‘Colomba’ or ‘Red Norland’ are prone to tuber rot if the seed is treated with a liquid seed treatment. The cut surface stays wet and does not suberize but rots. Tubers that are cut wet are more difficult to suberize and more prone to rot.

Photo Credit:

Eugenia Banks, Ontario Potato Board

Tuber wet surface after cut.

Photo Credit:

Eugenia Banks, Ontario Potato Board

Cut seed prone to tuber rot.

The varieties ‘Waneta’ and ‘Bannock Russet’ are prone to these problems. Emergence and stands are often nonuniform due to differential sprouting of bud-end and lateral eyes.

Photo Credit:

Steve Johnson, University of Maine Cooperative Extension

Late or erratic dormancy.

Extremely high soil temperature can burn the sprouts. This often is seen in sandy, hot soil when potatoes are emerging. The sprout number increases and new sprouts re-grow, but emergence is delayed and not uniform. Leaves can become malformed and appear to have herbicidelike injury.

Anaerobic conditions due to field flooding induce seed rotting usually caused by soft rot (see tuber soft rot).

Planting warm, freshly cut seed into cold soils can lead to poor stands, as can planting cut seed into cold, wet soils. The temperature difference between soil and seed pulp should be no more than 10 F (5 to 6 C).

Planting wet, pre-cut seed kept in storage with poor ventilation and high humidity can result in poor stands.

Seed cutters not calibrated properly can increase wedge and sliver pieces that are blind. Seed cutters not properly sharpened do not cut cleanly, making suberization difficult.

Dried vs. suberized cut seed: Cut seed that is not properly suberized but kept too dry can have dried skin (not suberized) and be prone to cracking and allowing disease entry and rot.

Photo Credit:

Steve Johnson, University of Maine Cooperative Extension

Burned sprouts from high temperatures.

Photo Credit:

Andy Robinson, NDSU/University of Minnesota

Malformed leaves from sprout heat stress.

Photo Credit:

Andy Robinson, NDSU/University of Minnesota

Seed rot from anaerobic conditions.

Photo Credit:

Andy Robinson, NDSU/University of Minnesota

Seed rot.

Photo Credit:

Steve Johnson, University of Maine Cooperative Extension

Poor stand because of seed rot.

Photo Credit:

Steve Johnson, University of Maine Cooperative Extension

Temperature shock on seed.

Photo Credit:

Steve Johnson, University of Maine Cooperative Extension

Poor seed storage can affect stand.

Photo Credit:

Steve Johnson, University of Maine Cooperative Extension

Poorly cut seed.