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.
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