ISSUE 16 AUGUST 26, 1999
SUGARBEET CROP UPDATE
Sugarbeet growers in Minnesota and North Dakota have planted a record acreage of 728,000 acres of sugarbeet in 1999. This includes 15,800 acres cultivated in western North Dakota to be processed at the Montana factory.
Growers have been successful in controlling Cercospora leaf spot to date. It is expected that we will be having another bumper sugarbeet crop. Harvesting will begin in some factory districts in late August. Best wishes to our growers for a successful, bountiful, and sweet, yes, high sugar content crop!
It is well known that Cercospora leaf spot is the most widespread and damaging disease of sugarbeet in Minnesota and North Dakota. Millions of dollars are lost each year because of Cercospora. Other sugarbeet diseases which are becoming more damaging and widespread are Aphanomyces root rot, Rhizoctonia root rot, and Rhizomania.
Aphanomyces root rot is spreading rapidly. It is estimated that about 10,000 acres of sugarbeet will be lost to Aphanomyces. The pathogen, Aphanomyces cochlioides is favored by warm, wet soils. To control Aphanomyces, plant tolerant varieties, use Tachigaren-pelleted seeds, plant early, improve drainage and cultivate when necessary to keep soil dry, increase length of rotation, control weeds since pigweed, lambsquarters, and kochia are alternate hosts, and avoid spreading contaminated soil.
Rhizoctonia root rot is caused by the fungus Rhizoctonia solani. Other hosts for this pathogen include crops such as soybean and edible beans, and weeds such as pigweed, lambsquarters, and kochia. The control measures for Rhizoctonia is similar in principle for Aphanomyces.
Rhizomania is caused by the beet necrotic yellow vein virus (BNYVV), which is spread by the fungus Polymyxa betae. The BNYVV survives in the soil for 15-20 years. There are no seed treatments to control this disease. Every effort should be made to prevent the spread of rhizomania contaminated soil. Until resistant varieties are available, sugarbeet should not be planted in contaminated fields.
Dr. Mohamed F. Khan
NDSU Extension Sugarbeet Specialist
FALL FERTILIZER SUGGESTIONS
Fall fertilizer will not be applied until late September at the earliest, but the following are guidelines on how to proceed given this is the last of 1999's Crop and Pest Reports.
Fall nitrogen should not be applied until calendar and soil temperature both indicate a better than average chance of low conversion of ammonia to nitrate following application. Having a large portion of the fall-N converted to nitrate in the fall sets up spring losses of N through leaching and early summer losses to denitrification. If ammonia/urea is applied before late September, there is a good chance like this year of a large proportion of N being converted to nitrate by freeze-up. Also, if soil temperatures are still warm (above 50 degrees F) after late September, conversion to nitrate is still relatively rapid. The best scenario is application after September 25 AND soil temperatures lower than 50 degrees taken from 6AM-8AM at the 4 inch level in a field representative of the acres to which N is be applied. As we saw this year, it does not take a flood to move N below the rooting zone, so preventing conversion is as important or more so than choosing the right rate.
Speaking of the right rate, soil testing is a must this fall. The wetter the year is, the more variability in the field. Consider breaking up the field into landscape zones to determine what different areas of the field test for N. Even if variable-rate N is not possible in your area, you will be able to interpret your soil test report much better and have more confidence in the results. Using the same N rate for all fields and all years is unreasonable and is a foundation for poor crop returns and fertilizer efficiency.
Urea application should be delayed one to two weeks at least following ammonia application. Urea converts to nitrate more rapidly than ammonia, so they should not begin together on the same date. The closer to freeze-up, the better it is. Of course, logistics of application and the ability to incorporate urea into the soil before bad weather must come into play, but realize that if urea is applied the end of September, the possibility that any ammonia will still be ammonia by November 1 if freeze-up does not occur is small.
Sulfur application is a tough problem in canola. Application of
elemental sulfur in the fall is not a solution to either sulfur leaching or elemental
sulfur breakdown. Since elemental sulfur to sulfate conversion (which is desirable and
necessary) is possible only when bacteria are active, conversion is slow in the fall and
stops during the winter. There is very little difference between spring and fall elemental
sulfur application effects on yield and neither is an option that is recommended.
Application of ammonium sulfate in the fall is an option only if you feel lucky. Although
sulfate is a little more strongly retained by soil than nitrate, sulfate can still leach
out of the root zone, and the areas of the field most in need (sandy areas, low organic
slopes) will be the areas leached out first.
The best option for sulfur is to apply a soluble sulfate form in the spring by a separate broadcast application or setting up a seeder to apply ammonium sulfate or another sulfate form with fertilizer and seed separated.
Dr. Dave Franzen
NDSU Extension Soil Specialist