ISSUE 14 August 26, 2010
SOYBEAN CYST NEMATODE SURVEY TO BEGIN IN SEPTEMBER
Soybean cyst nematode (SCN) is the most important soybean disease in the United States. In North Dakota, the disease is emerging, and has been confirmed in only three counties; Richland, Cass, and Dickey. However, the disease may be more widespread.
In an effort to determine how widespread SCN has moved we are collaborating with the National Agriculture Statistics Service (NASS) and the North Dakota Soybean Council (NDSC) to conduct a survey beginning next week. NASS enumerators will soil sample for SCN in approximately 120 soybean fields throughout the state. The soil will be processed at the plant diagnostic lab at NDSU, and the data will be presented at winter meetings. Only county wide data will be presented.
This information will help us understand where SCN is in the state and increase awareness of this critical disease.
SOYBEAN CYST SAMPLING
SCN is a threat to soybean producers in North Dakota. The disease can cause up to a 30% yield loss before above ground symptoms are present. Further, it is often hard to decipher those symptoms from other issues, such as IDC. The best way to detect the pathogen is through soil sampling, and the best time to soil sample for SCN is at the end of the season, including after harvest.
I would encourage soybean growers in ND, particularly those in the SE part of the state, to sample their fields for SCN. There are multiple labs that can process soil samples, commercial and University both. The most important aspect to management of SCN is early detection of the pathogen. IF SCN levels get high, successfully growing soybeans in the near future will be difficult. However, if SCN is detected before the population is high; the disease can be managed with resistant varieties and rotation.
For sampling instructions, many good resources are available. An excellent publication produced by the North Central Soybean Research Program is available at the Plant Health Initiative website www.planthealth.info/pdf_docs/SCN_Management.pdf
A video produced by Iowa State University is available at
Extension Plant Pathologist
NDSU IPM FIELD SURVEY WRAP-UP
The NDSU IPM field scouts have finished up their field scouting for the year, either going back to school or continuing with other jobs. Many thanks to Dixie Denis, Richard Glatt, Ryan Grieger, Suanne Kallis, and Asunga Manamperi for their scouting efforts this year. And thanks to James Walker, IPM mapper, and Roger Ashley, Greg Endres, Jan Knodel, Carrie Larson, Sam Markell, Lionel Olson, and Dan Waldstein for giving guidance to the scouts.
The scouts surveyed 810 wheat fields, 59 barley fields, 189 sunflower fields, 197 soybean fields and 56 canola fields during the growing season. Soybean and canola were surveyed primarily for insects. The scouts also put out insect traps in canola, sunflower and wheat fields. The following is a brief summary of the diseases the scouts found in wheat, barley and sunflower. Maps of the various pest occurrences each week and season summaries may be found at:
Wheat: Leaf rust: Only 3.4% of scouted fields showed symptoms of wheat leaf rust, and those fields had an average 3% leaf severity. Slightly more of the surveyed fields showed symptoms of stripe rust in 2010, with 4.7% of surveyed fields showing symptoms. Field severity of stripe rust was not measured, as it usually is a rarely observed disease.
Tan spot fungal leaf disease was by far the most common disease observed in wheat in 2010, with over 90% of fields showing symptoms, and an average severity of 3.4%, but a range of 1 to 45% leaf severity. Another fungal leaf spot, Septoria, was observed in 9% of surveyed fields with 1.9% average severity.
Barley yellow dwarf virus symptoms were observed in 2.7% of surveyed fields, while wheat streak mosaic virus symptoms were observed in 7.8% of surveyed fields. Bacterial leaf streak was observed in 6% of surveyed wheat fields.
Post-heading diseases observed included loose smut, found in 12.7% of post-heading fields, with an average of 6.5% of tillers infected - well above a seed treatment threshold in those infected fields. Head scab, or Fusarium head blight, was observed in 18.3% of post-flowering fields surveyed, with an average field severity of 4.1%. Glume blotch and/or bacterial black chaff were observed in 6% of post-heading fields.
Barley: The field scouts reported primarily fungal leaf spot diseases in barley. They observed net blotch, spot blotch, and/or Septoria in 64% of surveyed fields. Some fields had a combination of these leaf diseases present. The average severity of these leaf spot diseases was 8%.
Sunflower: Of the 189 sunflower fields surveyed, 30% showed symptoms of downy mildew. The average incidence of downy mildew infected plants in these fields was 4%. Sunflower rust was observed in about 21% of the surveyed fields with an average severity of about 1%.
NDSU Extension Plant Pathologist
UPDATE ON DISEASES OF SUGARBEET
Some of the common diseases that affect sugarbeet include Cercospora leaf spot, Fusarium, Rhizomania, and Rhizoctonia crown and root rot.
Cercospora leaf spot is the most damaging leaf disease of
sugarbeet in our area. It is caused
by the fungus Cercospora beticola
which does most damage in warm weather (80 to 90 degree days and over 60 degrees
in the night) and when it is rainy or when we have heavy dew. The fungus
destroys the leaves that are responsible for making the sugar in the plant
resulting in reduced tonnage and lower extractable sucrose.
Growers, over the years, have done a good job of managing Cercospora by using crop rotation, tolerant varieties, and fungicide applications. During the past five years, inoculum pressure in growers’ fields has been low and continues to be low in most areas. In a number of fields, there was no leaf spot. However, in several fields, individual plants with lots of disease are randomly distributed and serve as inoculum source. Some of these fields will need multiple applications at a minimum of 14 day intervals to control the disease. The fungicides which are currently most effective at controlling Cercospora leaf spot in fungicide trials at Foxhome are Proline, Inspire, Headline and a mixture of Topsin and Super Tin. Scouting of fields should continue – scouts should look for heavily infected plants scattered throughout the field.
The best way to control Cercospora leaf spot is to apply fungicides in a timely manner. For ground application, apply fungicides in 20 gallons of water per acre at 100 psi pressure; aerial applicators should use 5 to 7 gallons of water per acre for best results. Use the recommended rate of the fungicide; cutting rates will result in poor disease control and will quickly lead to the development of resistant isolates.
Fusarium yellows were first observed very early at the Moorhead research. Symptoms include interveinal yellowing and death of older leaves, sometime distinct death of half the leaf on one side of the midrib, followed by death of the younger leaves. When the roots of infected plants are cut in a cross section, there is a distinct darkening of the vascular system. Roots of infected plants will not store well in piles. The best way to manage Fusarium yellows is to plant tolerant varieties.
Plants infected by the Necrotic Yellow Vein Virus, which causes Rhizomania, are easy to observe in fields at this time. Plants infected with Rhizomania have distinctly fluorescent yellow-green leaves with hairy adventitious roots. The best way to manage Rhizomania is to plant resistant varieties. Therefore, in fields with a history of this disease, use resistant varieties approved for your factory district. Please note that all Roundup Ready varieties are resistant to Rhizomania. However, for fields with a known history of Rhizomania, check with your agriculturists, consultants, and seed company representatives for varieties that will perform well in heavy Rhizomania conditions.
Rhizoctonia solani causes Rhizoctonia crown and root rot of sugarbeet and root rot is becoming more prevalent, probably because of planting into warmer soils that have remained wet most of the season. Rhizoctonia solani can infect sugarbeet at all growth stages and results in wilting and death of plants. The fungus causes infection when soil moisture range from somewhat dry to wet and soil temperatures above 65 F. The fungus typically causes damping-off, and crown and root rot of sugarbeet. Damping-off occurs at the seedling stage when the fungus infects the hypocotyls resulting in rapid collapse of seedlings before soil emergence or post-emergence. Damping-off affects the plant population and ultimately reduces the yield. Crown and root rot infection occurs in older plants when the pathogen infects the petioles or the roots. Characteristic symptoms of Rhizoctonia include sudden wilting of leaves, and petioles of outer leaves may be blackened at the point of attachment to the crown. Crown and root rots, separately or collectively, are the most damaging phase of the disease and reduces yield significantly. The disease may also produce dry rot cankers on the root surface.
Fields with a known history of severe Rhizoctonia should be
planted to a tolerant variety. Crop
rotation with a non-host, namely wheat, early planting, proper drainage, and
avoidance of throwing soil into crowns of plants at cultivation will assist in
managing the disease. The use of
the fungicides Quadris or Proline at the 4 to 6 leaf stage or when the soil
temperature at the four inch depth is about 65 F will also help to control
Rhizoctonia crown and root rot.
There are also fields infected with Aphanomyces root rot. Warm and wet soils provide favorable conditions for infection by the fungus Aphanomyces cochlioides. In fields with a history of this disease, growers should use tolerant varieties treated with Tachigaren.
Growers need to plan management strategies early to manage diseases – planning should start with field and variety selection. Fields that has diseases at this time should be recorded so that appropriate varieties will be selected the next time these fields go into sugarbeet. Scout fields when necessary so that fungicides are applied in a timely manner, and when necessary, shorten the fungicide application intervals to prevent Cercospora leaf spot from causing an economic loss.
SUGARBEET CROP UPDATE
Early planting, adequate moisture, and favorable growing degree days have resulted in an excellent sugarbeet crop. Although the weather conditions were also favorable for many diseases of sugarbeet, the current sugarbeet crop will likely be the largest ever harvested. American Crystal Sugar Company and Minn-Dak Farmers Cooperative have their earliest start to harvest ever – August 17. Growers in southern Minnesota will start harvest on September 23. During pre-piling, about 15% of the crop will be harvested. The full harvest campaign will start on October 1. Please follow all safety rules at harvest and when transporting and piling beets.
Extension Sugarbeet Specialist
NDSU and University of Minnesota