Features Production Research
Keeping potato dry rot away from your field and storage

Every year, dry rot rears its head
in potato storages across the country. But some years, the infection
rate can be worse than others.

Dr. Rick Peters, a plant pathologist with Agriculture and Agri-Food Canada based in Charlottetown, P.E.I., says quality crop management, including excellent storage practices, can stop the spread of Fusarium spores and resulting dry rot outbreaks. Photo by Allison Finnamore

Every year, dry rot rears its head in potato storages across the country. But some years, the infection rate can be worse than others.

What causes the fluctuations year-to-year? The level of tuber damage going into storage, explains Dr. Rick Peters, a plant pathologist with Agriculture and Agri Food Canada based in Charlottetown, Prince Edward Island.

Dry rot in potatoes is caused by Fusarium spores, which are either already present in the soil of the potato field or introduced through infected seed pieces. These spores adhere to the tubers while they are growing in the soil and ultimately contaminate equipment and spread to other tubers during harvest, says Dr. Peters.

External symptoms of the disease include shrinking and shriveling of the tuber’s skin, usually around a central lesion. Internal symptoms appear as light- to dark-brown rot inside the tuber.

The key to a dry rot infection flaring up is whether the fungus
actually has an opportunity to enter the potato tuber through wounds on
the surface. According to Dr. Peters, there is no direct relationship
between the amount of dry rot in seed potatoes and the incidence of the
disease in storage. It’s possible for a grower to have a high incidence
of infection in his seed tubers but still have a low incidence of dry
rot in storage if tubers are not wounded during harvest and handling
operations, he explains. However, high levels of dry rot in seed can
lead to seed piece decay, poor emergence and reduced plant vigour
during the growing season.

Some examples of the kind of damage possible through an infestation of dry rot. External symptoms of the disease include shrinking and shriveling of the tuber’s skin, usually around a central lesion. Internal symptoms appear as light- to dark-brown rot inside the tuber. Photos courtesy of Dr. Rick Peters

Quality crop management, including excellent storage practices, can stop the spread of Fusarium spores and resulting dry rot outbreaks, says Dr. Peters. He recommends growers start with the cleanest seed potato stock possible, adding clean seed is critical to managing dry rot. Seed pieces should also be planted into quality soil and under suitable temperature conditions since they need to sprout rapidly, not decay, he advises.

The three main Fusarium species responsible for potato tuber dry rot are sambucinum (proven resistant to thiabendazole and thiophanate methyl), coeruleum and avenaceum. “The dominant Fusarium species you find in your field; you will find in your storage,” Dr. Peters says. “What you have in your seed; you will have in your storage.”

Besides infected seed potatoes, forages and cereal crops may also spread Fusarium to potatoes, says Dr. Peters. Research scientists with AAFC based in Charlottetown have been testing forages and cereals from across Canada for the presence of Fusarium species that can cause disease in potatoes.

Since cereals and forages are commonly used in rotation with potato crops. Dr. Peters says this issue is of utmost concern.

He recommends growers use a fungicide seed treatment and a seed diagnosis test to determine the main Fusarium species present in the seed, if available. He also suggests:
•     Reducing tuber injury during harvesting and handling.
•     Providing suitable temperature conditions to promote rapid wound healing in storage and then dropping the storage temperature.
•     Closely monitoring storage conditions.
•     Applying a post-harvest thiabendazole treatment, only if the main species of concern are those other than sambucinum, which is resistant to this chemical.