ISSUE 15 August 14, 2003
NDSU IPM SURVEY RESULTS, 7/28-8/1
NDSU IPM scouts surveyed 89 wheat and 34 barley fields the last week of July. All fields were in the northeast, northcentral and northwest portions of the state, as southern and central areas were either too mature for survey detection, swathed or harvested. Of the surveyed fields, 39 of the wheat were in dough to ripening stages and 27 of the barley fields were in dough to ripening stages (see maps).
Leaf rust was commonly found in surveyed wheat fields, with 62% of fields showing leaf rust on the flag leaf. The severity of leaf rust on the flag leaves was < 15% for most fields, but 6 fields had severity from 16-30%, 1 had severity from 31-47% and 1 had severity greater than 50%.
Tan spot or Septoria leaf infections also were common in many of the fields surveyed, with a majority having flag leaf severities between 1-15%, but 6 fields had severities ranging between 16-30%.
Of the wheat fields surveyed that were past kernel watery ripe, 36% had some level of Fusarium head blight (scab) (see map). The majority of these had scab field severity index levels below 5%. In barley, 32% of the surveyed fields showed some level of scab. The vast majority of these had scab field index values of less than 1% (see map).
ND IPM SURVEY
NDSU IPM survey scouts are winding down their activities for the summer and soon will be back at college or in new jobs. Currently, they are finishing up the survey on small grains in the north, and looking for soybean aphids, sunflower seed weevil, late season diseases and flea beetles in canola, and diseases in flax.
A big thanks to Lorlie Atkinson, Nathan Carlson, Cindy Leisy, Tammy Link, Patrick Metzger, Cody VanderBusch, and Nikki Zahradka for the great job they did this summer.
Dr. Joel Ransom, NDSU Extension Agronomist, has provided a report on occurrence of ergot in wheat in the Plant Science section of this Crop and Pest Report. He observed varietal differences in spring wheat plots in Ransom Co. this year and reports those differences he observed.
The NDSU IPM field scouts are reporting scattered fields of both wheat and barley with levels of ergot from 1-15% of tillers infected. From Joel Ransom’s report, it appears that ergot is common this year. I received a call today from a private crop consultant with some questions about ergot that he observed in Granite spring wheat.
What does a producer do with the ergot in the grain? Most of the sclerotia can be removed with modern cleaning machinery, unless broken pieces are present or the ergot bodies are very close in size to the grain kernels. Ergot may affect the market grade. Wheat or durum is graded as ‘ergoty" when it contains more than 0.05% by weight of the ergot sclerotia.
What about use of the grain for seed or use of a seed treatment? No seed treatment is available that will kill the ergot sclerotia or prevent them from germinating. Seed with ergot may be a source of contamination into a non-infested field, if conditions are favorable for infection next year. The ergot sclerotia will not germinate if buried more than 1-2 inch deep.
What are other sources of ergot? Wild grasses along roadsides and in waterways may have been a source of the ergot bodies that produced spores for this year’s infections. These grasses should be mowed before flowering, to prevent ergot infections and prevent ergot bodies from falling to the ground.
Do insects spread the disease? Insects visiting wheat heads from other grass flowers can spread the disease into the open wheat florets. Insects are attracted to the honeydew or sticky substance exuding from infected flowers. The abundance of grain aphids this year may have accelerated spread of the ergot fungus.
Do fungicides used to control scab help control ergot? Chemical control of the ergot fungus (Claviceps purpurea) has been investigated in Europe, but with limited success. NDSU has no local information on the effect of fungicides such as Folicur or Tilt on the ergot fungus. It is not expected that these fungicides, which were used to suppress scab this year, would have much effect on the ergot fungus.
2003 FINAL CEREAL RUST BULLETIN, USDA, ST. PAUL, MN
The final edition of the 2003 Cereal Rust bulletins, published by the USDA Cereal Disease Laboratory, St. Paul, stated that:
a) Wheat leaf rust was widespread this year and severe in some areas of the US. The bulletin states that trace to 60% leaf rust severities were observed in spring wheat varietal plots in central and eastern ND plots, and up to 40% severities were observed in some ND commercial fields. The spring wheat cultivars currently grown have less effective resistance to leaf rust than those that were popular 10-15 years ago.
b) Wheat stripe rust developed early and was more severe than usual throughout the US. In late July, active stripe rust pustules were observed in wheat varietal plots throughout the state of ND. During the last week in June, winter wheat fields and plots in south central SD had stripe rust severities from trace to 60%.
c) Stem rust in various cereal crops was found throughout the northern Great Plains, but developed too late to cause any yield loss.
d) Oat stem and crown rust severities were light this year.
NDSU Extension Plant Pathologist
CRISIS EMERGENCY EXEMPTION FOR TILT ON DRY BEANS
The North Dakota Department of Agriculture declared a crisis emergency exemption for the use of Tilt (Syngenta) on dry beans for control of bean rust. The exemption is effective from August 7 to August 22, 2003. The recommended use rate is 4 fl. oz. per acre. No more than 12 fl. oz. of Tilt per acre may be applied in a season.
CHARCOAL ROT OF SOYBEAN
In August of last year (2002), a soybean disease new to North Dakota, known as charcoal rot, was observed in Richland County. Charcoal rot is caused by the fungus Macrophomina phaseoli. The disease generally develops under dry conditions. Diseased plants typically occur in patches, and symptoms include early maturing, wilting, and grayish to silver discoloration of the lower stem and root area. In the advanced stage, small black specks (microsclerotia) may be found on the outer stem and in the pith area. Recommendations for charcoal rot management include avoiding high seeding rates and growing soybeans once every 3 to 4 years in fields known to have charcoal rot.
FUSARIUM YELLOWS OF SUGARBEET
Fusarium yellows of sugarbeet, caused by the fungus Fusarium oxysporum, is a soilborne disease of growing importance in the Red River Valley. The disease was first verified as being in the area in August 2002; however, Fusarium yellows type symptoms had been observed in years prior. Symptoms first appear on older leaves as a yellowing between the larger veins. In some instances, only one-half of a leaf may be symptomatic. Wilting may occur during the day, but plants generally regain turgor overnight. Eventually, leaves may die and collapse in a heap around the crown. External root symptoms are not present, but discoloration of the vascular tissue may be observed if roots are sliced open. Because this disease is new to the area, resistant varieties are not available. Crop rotation will slow down the buildup of inoculum in the soil.
Carl A. Bradley
Extension Plant Pathologist