Before Black Dot Hits

Tips for preserving potato yield and quality

Published online: May 28, 2018 Fungicide
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This article appears in the June 2018 issue of Potato Grower.

While black dot disease may not receive as much attention as white mold or early blight, for some growers, black dot can be a persistent problem in their fields. The impact of black dot can be equally as detrimental to potato yield and quality as diseases that are brought up more often in disease control conversations.

“Black dot is not a disease that is as widespread as others,” says Curtis Rainbolt, BASF technical representative. “But for growers who do have it in their fields, it tends to show up year after year. If growers know their fields have a history of the disease, they should work with a chemical representative or crop consultant in their area to help control it.”

By working with a representative or crop consultant, growers can determine a plan that works best for their operation while reducing the damaging effects on their crop.

Protecting Yield and Quality

Controlling black dot can be more challenging due to its latent period. Infection in the potato plant can happen early, but signs of the disease don’t show up until much later in the growing season. By the time disease symptoms shows up, yield and quality are already at risk.

“There are two main parts to what can happen to a potato plant when this disease hits. The first part is a yield problem,” says Rainbolt. “This disease can cause the vine of a potato crop to die early, reducing the photosynthetic capability of the plant and the amount of nutrients delivered to the crop, ultimately reducing yield.”

Rainbolt also points out the second part of potato production affected by this disease: quality reduction. When black dots appear on the tuber, the quality of a grower’s crop is downgraded, meaning the grower has to sell it at a lower price point.

In addition to affecting yield and quality, black dot disease can also cause problems during storage. When placed in storage, potatoes infected by black dot can be more vulnerable to rotting, further reducing a grower’s yield. With so many risks associated with uncontrolled black dot, growers should develop a disease management plan for their crop early.

Know Your Field and Manage It Well

Since signs of black dot disease are delayed from the time of infection, potato growers must be diligent about disease management practices as well as have a thorough knowledge of their fields’ susceptibility to this disease.

“One of the best ways to control this disease is to know the field’s history,” says Rainbolt. “From there, growers can select varieties and make other management decisions to lessen the risk of black dot.”

These decisions should be implemented as part of a disease management plan that is determined well in advance of the growing season. This way, growers can stay ahead of the disease rather than acting when the damage to a crop’s quality may be irreversible.

Part of this disease management plan should be working during the growing season to reduce stress on a crop. The more stress there is on a crop, the more susceptible it is to disease.

“There are always things growers can do to reduce stress in their fields during the growing season, such as watering and nutrient management,” says Rainbolt. “However, there are some decisions growers need to make far in advance of the growing season to manage black dot.”

Rainbolt mentions crop rotation as a long-term consideration for growers. Although black dot disease can be transferred through seeds or the air, it’s typically a soil-borne disease. This makes crop rotation an important consideration for growers whose fields have a history of the disease.

“Crop rotation helps reduce the risk of black dot,” says Rainbolt. “The longer your rotation is, the more you can reduce the fungus or inoculum in the soil, but it doesn’t totally eliminate it.”

Rainbolt also recommends growers consider using fungicides as a part of their disease management plan. Fungicides, when applied prior to disease development, can be an effective tool for controlling black dot.

“University recommendations for control of black dot include use of a strobilurin fungicide early in the season,” says Rainbolt. “Strobilurin products are recommended because they have good efficacy. Priaxor Xemium brand fungicide is a product we recommend growers use to control black dot because it has the strobilurin product in it, and it has good activity on the disease.”

Rainbolt says the fungicide application should occur at the 10-inch rosette stage of the growing season, if conditions are favorable for disease development, in accordance with the label.

The use of fungicides to control black dot should exist within an integrated disease management plan. Growers can work with a BASF representative or crop consultant in their area to determine a plan that best fits their needs and preserves their potato crop’s yield and quality.

For more information, growers can contact a local BASF representative or visit


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