ISSUE 2 May 17, 2007
2006 WHEAT DISEASE SURVEY RESULTS - PREDICTOR OF 2007 DISEASE RISK?
The 2006 growing season in North Dakota was relatively dry and warm, and these conditions were reflected in the low level of most diseases observed during the 2006 wheat disease survey. NDSU IPM field scouts examined 1150 wheat fields across all ND counties during last year’s growing season. Some of the most common and least common diseases observed and their prevalence and severity were:
1. Wheat leaf rust: found in 11.9% of fields, average severity was 5.6%
2. Stripe rust: found in 1.7% of fields; low severity
3. Tan spot: found in 80.3% of fields; average severity only 5.4%
4. Septoria disease complex: found in 16.3% of fields; severity 12.9%
5. Fusarium head blight (scab): found in 7.3% of fields (lowest since 1993); average severity < 1%
6. Wheat streak mosaic virus (WSMV): observed only in 1.4% of all fields surveyed, but where it occurred it was fairly severe.
Low occurrences or severities of diseases such as tan spot and scab, diseases which are caused by fungi that carryover in residue, may indicate a lower potential risk for 2007. However, rainfall, soil moisture, and relative humidities at key growth stages will be the deciding factors, because the fungi causing these diseases have the potential to reproduce rapidly, even with low inoculum levels, under favorable, wet environmental conditions. In other words, last year’s occurrences are not very good predictors of this year’s disease levels. A dry, hot summer would be more favorable for wheat streak mosaic virus, as the wheat curl mite transmitting the virus would be more active.
CEREAL RUST INFORMATION
The USDA Cereal Disease Lab, located in St. Paul, MN, provides a bi–monthly update of cereal rust situations in the United States throughout the growing season. This information includes rusts on winter wheat, spring wheat, barley, oat, and rye. Contributing to this information are the USDA cereal rust scientists who do extensive field surveys in the spring and summer, and university cereal workers associated with the various states who grow cereals. The information is published on-line in The Cereal Rust Bulletins, which can be found at:
The latest bulletin (May 15) indicates that wheat leaf rust is widespread throughout the southern U.S. High levels of leaf rust were observed from central Oklahoma to central Kansas on susceptible varieties, and some observations have also been made in south central South Dakota. Levels in South Dakota were trace to less than 2% severity. Wheat stripe rust also has been reported in southern Plains states, but at low severities. North Dakota’s wheat survey begins next week, and scouts will be looking for occurrence of leaf rust in ND winter wheat fields.
The Cereal Rust Bulletin also indicated oat stem rust and oat crown rust were increasing in Texas, while barley rusts were not being observed in Plains states.
WINTER WHEAT AND EARLY SEASON FUNGICIDE
Winter wheat in the 4-5 leaf stage may benefit now from an early season fungicide application in combination with herbicides. Recent spring rains and moderate temperatures may activate the tan spot fungus in wheat residue and make these winter wheat crops vulnerable to tan spot infection.
Data from NDSU winter wheat studies show yield response to early season fungicide application in years when weather was favorable for wheat and disease development. Studies across winter wheat cultivars at Lisbon, ND over 3 years indicated yield responses to a single early season fungicide application ranged from 0 to 6 bushels, depending on year and cultivar.
Early season fungicides tested included half of the full label rates of Tilt (or other propiconazole products), Quilt, Stratego, and Headline. Subsequent applications at flowering provided additional yield and disease control.
Ext. Plant Pathologist
Area Extension Agronomist
North Central Research/Extension Center, Minot
North Dakota State University, Fargo
PLANTING SOYBEANS? CONSIDER A SEED TREATMENT
In North Dakota, the weather can turn wet and cold in a hurry. When soil is cool (60o F or less) and wet for prolonged periods of time soybeans germinate slowly, making them more vulnerable to seed and seedling diseases. Considering recent heavy rains in parts of the state, a seed treatment may be beneficial.
Other factors that may contribute to seed or seedling diseases of soybeans include tight rotations, heavy and/or poorly drained soil, no-till or reduced-till, and early planting. These can facilitate a buildup of pathogen populations or provide a favorable environment for disease development. A history of disease in the field is also an indication that you may be at greater risk for seedling infection, making a seed treatment profitable.
Even when conditions are less favorable to the pathogens, a seed treatment may not be a bad deal. Research conducted in North Dakota over multiple years and locations suggests that on average, the cost of the treatment was recovered. When data for the 14 environments in the study were averaged, soybean returns from plots with seed treatments were approximately $10-$20 an acre higher than plots planted with untreated seeds.
Numerous pathogens, including Rhizoctonia, Pythium, Phytophthora, and Fusarium species can damage soybeans, but most chemicals do not control all of the pathogens. Metalaxyl or mefenoxam will control Phytophthora and Pythium, while azoxystrobin, fludioxonil, and others control Fusarium and Rhizoctonia. A product that contains combinations of the chemicals will give you the broadest spectrum of control against the numerous pathogens.
For additional information about seed treatment products refer to the 2007 North Dakota Field Crop Fungicide Guide, available through the NDSU Extension Service. Always follow manufacturer’s labels.
Extension Plant Pathologist
PLANT POPULATION FOR HIGH SUGAR BEET YIELD AND QUALITY
It is sugar beet planting time again! Our research shows that maximum recoverable sucrose per acre correlates well with plant population. Research done at North Dakota State University and the University of Minnesota showed that a plant population of 175 to 200 plants per 100 foot of 22 inch wide rows was ideal for maximum recoverable sucrose per acre. It is important that the plants be evenly spaced within the rows.
At lower plant populations – say at 100 to 125 plants per 100 foot of row, roots tend to be somewhat larger but there is generally a reduction in yield because of the lower population, and sucrose concentration decreases resulting in higher processing costs. Lower plant populations take longer for the canopy to completely cover the soil resulting in a more costly weed control program.
Plant populations of more than 225 plants per 100 foot of row result in too much competition among the plants and consequently smaller sugarbeet roots and lower recoverable sucrose per acre compared to plant populations of 175 to 200 plants per 100 foot of row. Defoliation becomes very difficult at such high plant populations. Sugar beet fields with 225 plants per 100 foot of row planted at 22 inch row spacing should be thinned to about 175 to 200 plants per 100 foot of row.
Plan to have a good plant population of 175 to 200 plants evenly spaced per 100 foot of row for highest sugar beet yield and quality. Please note that growers who use 30 inch row spacing should aim for about 215 to 225 plants per 100 foot of row to get highest yield and quality.
Protect your plant stand from insects by using correct rates and proper placement of insecticides, and from wind by planting a cover crop of barley or oats seeded at half a bushel per acre. The cover crop should be controlled when the beets are at the 3 to 4 leaf stage.
What happens if pests, wind or crust reduces plant population in the middle of May to less than 100 plants per 100 foot of row? If beets are still emerging, it is possible that a few more may emerge from the ‘cracked’ planted row especially if there is a rain. Replanting may be an option if the population is about 75 plants per 100 foot of row. However, a dry spell after planting may also lead to a disaster. Weed control becomes even more crucial and important with low plant populations.
Extension Sugarbeet Specialist
NDSU & University of Minnesota