March 2012
Protecting tuber quality: Potato seed treatments set solid foundation for successful season By Bill Schaefer

Seed treatments help protect your investment, while laying a solid foundation for the remainder of the growing season.

Willie Kirk, plant pathologist at Michigan State University, said growers in Michigan must be vigilant against three main diseases: seedborne late blight, rhizoctonia and fusarium seed-piece decay.

“What we recommend are products with mancozeb components,” Kirk said. “Maxim 4FS, followed by a mancozeb dust treatment. We don’t like dust treatments from a health standpoint, but they enhance suberization and prevent seed-to-seed spread of disease at cutting.”

The Maxim 4FS treats silver scurf, rhizoctonia and fusarium immediately, followed by some treatment containing mancozeb to prevent the transmission of late blight.

“The reason I like mancozeb: It prevents the spread of late blight at cutting,” Kirk said. “When we do it in the lab, it takes 30 seconds of contact with the inocula to spread late blight.”

Kirk said the ideal seed treatment would be a broad-spectrum product effective against oomycetes, partnered with a product effective against true fungi that came in a liquid formulation.

The broad spectrum would fight the pathogens that cause late blight, pythium and pink rot, while the second product would fight rhizoctonia, fusarium and silver scurf.

Mancozeb treatments include Nubark Mancozeb by Wilbur-Ellis, Maxim MZ by Syngenta, Moncoat MZ by Gowan, Tops MZ Gaucho and Evolve by Bayer CropScience, and Curzate 60DF by DuPont.

Kirk said that a product like Revus Top is an option when looking for a broad-spectrum agent.

Idaho plant pathologist Phil Nolte advises Idaho growers to be “real careful about late blight again.”

Nolte recommended that growers not only use a seed-piece treatment active for late blight, but use a treatment effective for dry rot. He said conditions have been very conducive for rhizoctonia to thrive in the past three seasons.

“The last few seasons we’ve had cool, wet planting seasons and delayed emergence,” Nolte said. “It can make the rhizoc canker worse. A couple of things happen. Most of it is on the seed or in the soil. When it’s on the seed piece, it’s going to sit there. The black survival structures of the Rhizoc will thrive in the cool, moist soil, and the fungus will be activated. The fresh sprouts from the eyes of the tuber are vulnerable to the rhizoc canker.”

For rhizoctonia management, Nolte advises growers to plant shallower and hill up later. Rhizoctonia is extremely sensitive to UV light, and the sooner the plants emerge the stronger they become.

Delay your planting, Nolte said. You want warm soil temperatures: 50˚ F to 55˚ F is ideal. Seed is encouraged to emerge quickly.

“The other disease that is certainly a potential problem is silver scurf,” Nolte said. “If you’re growing red skin or white skin potatoes, you’re going to want to consider using something conducive for silver scurf.”

University of Wisconsin plant pathologist Amanda Gevens concurred with Kirk’s and Nolte’s recommendations to treat seed with fungicides containing mancozeb, but with the proviso to maintain seed under proper conditions to suberize prior to planting.

Gevens recommended a Curzate seed treatment to limit spread of late blight from seed to seedling. Gevens advised growers that proper sanitation of seed cutting equipment and properly sharpened knives are important components of an overall good management program.

Fungicide efficacy increases with proper handling of seed; limit the bruising and properly warm up seed prior to cutting.

In-furrow treatments for rhizoctonia, fusarium seed decay and silver scurf include Quadris combined with Maxim 4FS, Maxim, Maxim MZ, Moncoat MZ, Moncut, Tops MZ, Headline, Moncut and Dynasty.

75 Applewood Dr. Ste. A
P.O. Box 128
Sparta, MI 49345
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