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Downy mildew in sunflower fields
June 22, 2004

Source: Agronomy Update, Mycogen Seeds

"Downy mildew could be a serious problem this year in sunflower fields if conditions are favorable for its development," says Bruce Due, District Agronomist, Mycogen Seeds. "Sunflowers are most susceptible if moderate to heavy rain splashes soil up onto newly emerging plants prior to the four-leaf stage. Most areas have some potential to contract the disease, but the eastern part of the sunflower growing area is most likely to see the disease again."

Apron XL® seed treatment has provided nearly complete control in the past. But, downy mildew has developed several new strains that are resistant to Apron seed treatment, causing the disease to show up once again in commercial sunflower fields. Apron has no effect on the new strains, Due explains. Currently, there are few hybrids commercially produced that have complete resistance.

Downy mildew causes the plant to form a white, cottony growth on the underside of the leaves. These leaves have a light discoloration on the top of the leaf. Even though this disease is contracted very early in the growth stage, it may not show up until the four-leaf stage or later. "Most of these affected plants will die; however, a few survive to produce stunted plants that produce very little seed," Due explains. "Others will die at the seedling stage."

Secondary infection can also occur in plants. These plants tend to get the disease late in the season, and although some seed set may occur on these plants, yields will be reduced. Secondary infection can occur by spores being moved around in a field by animal movement, machinery and wind.

"If downy mildew is detected in a field, delay cultivation until the plants are dry," Due advises. "This will help avoid spore movement down the row by machinery. Rain, wind and running water can also spread downy mildew spores. Crop rotation helps control the disease, but virgin sunflower fields can still contract downy mildew because of its ability to move."

Mycogen Seeds has hybrids under development that will have resistance to all current strains of downy mildew. We anticipate availability in large numbers in the next two years, Due concludes. The search for a seed treatment to replace Apron is also underway, but to date, none have been identified as effective against all strains.

For more complete information on downy mildew, visit the North Dakota State University Extension Web site: http://www.ext.nodak.edu/extpubs/plantsci/rowcrops/eb25w-6d.htm.

Mycogen Seeds is an affiliate of Dow AgroSciences LLC.  Mycogen Seeds is the leader in Silage-SpecificTM corn, the largest sunflower seed producer, and a leading producer of seed corn, alfalfa, soybeans and sorghum.

®™Mycogen and the Mycogen M logo are trademarks of Mycogen Corporation.
®Apron XL is a trademark of Syngenta Group Company.

Agronomy Update, Mycogen Seeds

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