March 11, 2005, updated on March 18, 2005

Soybean rust as seen under a 14X hand lens.

Potential impact of soybean rust in Nebraska

USDA estimated favorable areas for soybean rust disease development based on temperature and moisture records over the last 30 years. A large portion of the soybean production area of Nebraska is in the 15- to 18-year range with a smaller area in the 12- to 15-year range, indicating that soybean rust would be likely in Nebraska about 50% of the time. (Map links to larger version.)

Nebraska is located on the western “fringe” of soybean production in the north central states. As a state on the edge, we see the extremes of growing conditions. For example, average precipitation ranges from over 30 inches in the southeast corner of the state to less than 16 inches in the Panhandle.

The very things that often complicate crop production in Nebraska, such as inconsistent precipitation and the need for irrigation, may make our crop less susceptible to soybean rust. Also, the extreme temperatures typical in late July and August could reduce our potential for soybean rust. As soybean rust does best at temperatures between 65^oF and 85^oF and requires moisture for development, the potential for rust to be a significant problem every year in Nebraska is low in our dryland fields.

However, irrigated fields would have more favorable conditions for disease development. As a result of our natural, year-to-year environmental variation, we will experience variable degrees of soybean rust each year. Based on the USDA soybean rust risk map, which includes ambient weather conditions, Nebraska has been predicted to have severe soybean rust problems about 50% of the time in most of the state. It is important to note that the risk map does not include irrigation and in 2004, 55% of the Nebraska soybean crop was irrigated.

My personal prediction is that soybean rust could possibly increase the profitability of Nebraska soybean producers. This is based on the following points:

1. Soybean rust will result in many U.S. acres being treated with fungicides one to two times per year and Nebraska should not have to do this all years.
2. Soybean rust is predicted to overwinter in the southern United States and will not occur at the same time each year in the upper Midwest.
3. All indications are that soybean prices will increase when rust arrives and fungicide applications become common. Prices will increase to reflect the increased production costs; however, Nebraska producers are not likely to have increased costs every year.

Backlit soybean leaf showing severe soybean rust. (Brazil February 2005)

Soybean rust, also referred to as Asian soybean rust, is caused by Phakopsora pachyrhizi and is an aggressive pathogen that has spread in the past 10 years from Asia to Zimbabwe, South Africa, Paraguay, Brazil, and now the United States. Yield losses can be severe and have ranged from 10% to 80% of a field. In the last few years, Brazilian soybean producers have been significantly affected by soybean rust. In 2002-2003 they spent $600 million for fungicide applications and in 2003-04 it’s estimated they spent more than $1 billion. USDA estimates U.S. losses could be in the range of $640 million to $1.3 billion in the first year and $240 million to $2 billion in subsequent years, depending on the severity and extent of spread. I want to make note of a key point: This disease is manageable. U.S. producers will adapt to the needed management and our soybean crop will continue to be strong.

• Different spray nozzle tips
• Different spray carrier volumes
• Different spray pressure
• Different orientation of the spray tips
• Slower travel speed

Many think that a fine spray particle size provides the best coverage and penetration. At this time, I recommend using a fine spray particle size that is almost in the medium category. While very small spray droplets can increase coverage, they are susceptible to off target movement and evaporation. For example, with a Spraying Systems XR11003 nozzle you would use 30 psi while if you use a XR11005 you would use 60 psi (see Table 1). If nozzle tips are available in ceramic, they probably are your best investment because of their superior wear life.

To increase penetration and coverage, angle the spray tips back 450 and ensure that the height of the spray boom provides 1000 overlap at the target height – the top of soybean plants (see Figure 1). Some may suggest using drops, but I would not recommend using drops.

If you have to use a higher boom height, reduce the angle to less than 450 so the pattern provides a 100% overlap. One hundred percent overlap is where the pattern from the nozzle tip ends up under the next nozzle (see Figure 2).

Since this will be the first year for this disease in Nebraska, we don’t know exactly how it will respond to our conditions. The following observations may be helpful in assessing your risk and determining whether a fungicide application is needed.

Loren Giesler, Extension Plant Pathologist, examines a fungicide trial in Brazil in February 2005. Researchers hope to learn from the experience of producers and researchers in Brazil when countering the expected onset of soybean rust in the United States. Brazilian field trial shows the effect of fungicides in nontreated and treated (right) fields.

• Irrigated fields will be at a greater risk as this is a moisture driven disease. In Brazil, outbreaks are associated with rain and rust is known to develop in the pivot irrigated fields used for winter seed production.
• Based on my recent discussions with Brazilians, night temperatures appear to affect disease development more than high temperatures during the day.
• The USDA predictive models do not include irrigation (55% of the Nebraska crop is irrigated).
• I would not recommend fungicide application to historically low-yielding fields. Do the math and determine what percentage yield savings you need to pay for the fungicide. This will quickly lead you to the higher yielding fields.
• Application timing is everything (especially when you miss the target): Experience has shown Brazilian producers that to stay ahead of this disease, the best return is a preventative treatment. Consider preventative treatments on high yielding fields (especially irrigated) when rust is an immediate threat based on the disease forecast for spore movement.
• While the Disease Forecasting Model has not been validated for the United States, it is the best chance we have at predicting where soybean rust will most likely appear next.
• If soybean rust is detected in the area, but is not present in the field, a preventative fungicide can be used.
• If soybean rust is detected in the field, a curative fungicide should be used if an application is made.
• In poor yielding, dryland fields, rust will most likely not be a significant problem, as conditions for poor yield generally don’t favor rust development.
• A range of planting dates will spread the time when plants are flowering, allowing more time for fungicide application.

At this time, the fully labeled products should be used as preventative treatments and should not be used once rust is established in the field. The Section 18 products are a result of a national request and can be used in Nebraska when rust has been identified in the United States. Rust does not need to be confirmed in Nebraska for the Section 18 to be in force. The applicator is required to have possession of the Section 18 label at the time of application.

In a future CropWatch article we will discuss the differences in these products, their modes of action, and why your selection may change depending on whether it’s a preventative application or rust is present in the field.

Loren Giesler
Extension Plant Pathologist

The southerly jet appears in late April or early May but is primarily limited to the area south of Nebraska (40°N) until June. From June to September, the jet intensifies and extends northward into Nebraska. Because the jet has strong wind near the surface level (Figure 1b), it can pick up rust spores from an infected area and carry them to northern states, where the spores can fall with the rain. This jet has two peaks, one in June-July and the other in September. The June-July peak occurs during a key growth stage for Nebraska soybeans, thus its potential for spreading soybean rust at that time is alarmingly large.

Although more than the jet flow will influence the potential for soybean rust in Nebraska, knowing the jet variation and prediction of jet intensity and northward extension can help producers determine the probability of rust arrival and develop plans to control rust infection. Growers should pay attention to this jet pattern during the season and combine jet variation with the rust monitoring report at the Nebraska Soybean Surveillance Network to make treatment decisions.

Steve Hu
Extension Climatologist

Figure 1a: Average 850mb (~0.7miles above the sea level) flow 1-15 July. Arrow length shows the wind speed and the scale is given in the lower right. Color shading indicates southerly wind speed greater than 4ms-1, increment is 1ms-1 (1ms-1=2.24miles/hour). Figure 1b: Average vertical cross section of summer southerly wind in meter per second along 30ºN latitude at the different longitudes. The ordinate shows height from 1000 to 500mb, roughly from the sea level to ~3miles above. The shaded area in the center of the figure shows the southerly jet, which has large southerly wind speed at the near surface levels. Figure. 2: Annual variation (development) of 850mb southerly wind across the latitude (shown in the vertical axis) averaged in the longitude channel of 97°-100°W (see Figure 1a for the longitude locations). Wind speed scale is given on the right of the figure, in meter per second (x2.24miles/hour). Red color indicates the southerly jet (both intensity and longitudinal stretch).

Meeting location changed Due to overwhelming response, the Soybean Rust First Responder training to be held March 30 at Norfolk has been moved to a larger facility -- the Northeast Community College (NECC) Ag Complex. The complex is near the junction of Benjamin Street and Hwy. 35. (A different meeting location was previously announced in CropWatch.)

The program will be offered March 29 from 8:30 a.m. to 1 p.m. at the University’s Agricultural Research and Development Center (ARDC) near Mead and March 30 from 9:30 a.m. to 2 p.m. at the Northeast Community College Ag Complex in Norfolk. This training is part of the University of Nebraska Cooperative Extension’s Crop Management Winter Programs. The program is designed for, but not limited to: crop consultants, certified crop advisors, growers, cooperative extension personnel, state and federal inspectors, master gardeners, and others involved in plant health management. Those attending will be able to enhance their pest identification skills, learn about exotic pest issues that may threaten Nebraska agriculture, and become a registered First Detector.

This class is limited to 65 participants so early registration is recommended and will help ensure that appropriate class materials are available. This training session, which costs $25, is available at a reduced rate courtesy of the Great Plains Diagnostic Network. Fees include lunch, refreshment breaks, and workshop and reference materials.

If no effective control measures are available or there are insufficient amounts of chemicals available for effective control, the resulting loss of production is covered. It will not be a covered loss if there are sufficient control measures available but the insured elects not to use them. Failure to purchase and apply recommended control measures will result in assessing uninsurable causes of loss. Producers are responsible to keep informed of soybean rust outbreaks in their area.

Insured producers should follow developments as to the identification and spread of Asian soybean rust and continue to stay informed and updated concerning appropriate treatments that may apply to their situation. Appropriate treatment may vary from timing of application (pre- or post-discovery of the disease), frequency, and choice of chemical or other determining factors. If crops become infected, discovery of the disease and any recommendations received regarding the application of appropriate control measures must be documented.

Doug Jose
Extension Farm Management Specialist

Many producers now apply most of their nitrogen in the spring. Depending on nitrogen source and timing, spring application offers some advantages, as well as some disadvantages.

Other nutrients?

Generally, spring fertilization means nitrogen fertilization. Phosphorus should have been applied in the soil or seed furrow last fall to benefit this spring’s crop. Most winter wheat is grown on fine textured soils where there is little evidence of yield increases from adding sulfur. If you grow irrigated wheat on sandy soils and the irrigation water contains less than 6 ppm SO₄-S, you may need 10-15 lb sulfur, depending on what was applied last fall. Recent Nebraska research has shown that chloride (usual source 0-0-60) may enhance yields in eastern Nebraska where soil chloride levels are low (less than 30-40 lb/a in a 2-foot soil sample). Research in western Nebraska has not shown consistent responses even at low chloride levels.

Spring nitrogen management

Forecasts call for above normal precipitation until about the end of next week, said Al Dutcher, state climatologist in the university's Institute of Agriculture and Natural Resources.

"We're likely to see an uptake in storm activity, but these storms need to drop significant precipitation along the Front Range of Colorado and Wyoming," Dutcher said. Snow pack levels in the central Rockies have dwindled from near normal conditions in January to less than 85% of normal as of March 14. Even a couple of big snow storms may not bring snowpack levels back up to normal.

"Levels have consistently decreased since January, and we're running out of season," he said. "Snowpack levels peak around April 15, so we only have about the next 30 days or so to bring that snowpack back up to normal."

In addition, Platte River basin runoff projections are currently pegged at 585,000 acre-feet of water, much of which will be held by Wyoming reservoirs. Some of this water will make its way toward Lake McConaughy, but not enough to offset expected irrigation delivery restrictions.

"Lake McConaughy will probably peak somewhere between 32% and 35% of normal," Dutcher said. "If normal to above normal temperatures materialize this growing season, Lake McConaughy will probably be very close to, or at, minimum pool level as we get to the end of this irrigation season."

Last year's unseasonably cool summer kept some of that water demand down, and Lake McConaughy levels ended up at the upper end of its spring projections.

"Although not impossible, it may be asking a lot to see two consecutive summers with temperatures ranked in the top five coolest on record," Dutcher said.

It also is expected that the Platte River again will go dry this summer unless it's an unusually wet season. Much of this will be the result of the Central Nebraska Public Power and Irrigation District conserving Platte River water by halting releases from Lake McConaughy to conserve a limited water resource, Dutcher said.

Harlan Reservoir looks to be in worse shape than Lake McConaughy -- unless the Republican River Basin has a significantly wet spring, there may not be any deliverable water coming out of that reservoir this summer, he said.

However, March and April are critical because more precipitation falls during those months than the December through February period. In addition, snowfall can be significant given the right conditions, and the snow typically has a significantly higher water equivalency.

"We also need timely precipitation for the state's winter wheat crop," Dutcher said. In addition, lack of moisture and high winds across the state have increased the risk of grassfires.

"We need moisture to offset these problems," he said.

Extreme ridging in the western United States during the last 30 days has been responsible for the region's dry weather. However, the 90-day forecast is showing wetter than normal patterns, Dutcher said.

"There are a lot of questions right now," Dutcher said.

Fortunately, a dry winter doesn't necessarily make a dry summer more likely. However, there is a slight tendency for a wet spring to be followed by a wet summer. However, even if Nebraskans do see a wet spring and summer, drought will continue to be a concern for agriculture, recreation, wildlife and water supplies.

The most common grasses interseeded into alfalfa are orchardgrass and smooth brome, but other grasses like endophyte-free tall fescue, meadow brome, wheatgrasses, and creeping foxtail also can be used. In addition, other legumes like red clover can be seeded for short-term pasture or birdsfoot trefoil can be used if you plan to graze the pasture more than three years. This will add diversity to your animals' diet and help assure good legume growth for several more years.

You must get these new seedlings off to an early start, so be sure to interseed as soon as soils thaw and conditions allow tractor and drills to operate properly. If your alfalfa still is relatively thick and vigorous, take an early hay cutting, probably during the first week of May, well before buds form. This will allow sunlight to continue to reach new seedlings below the alfalfa. Then use your good judgement regarding competition from the existing alfalfa for subsequent hay cuts. By mid- to late summer you should be able to start rotational grazing of the field.

Interseeding grass into existing alfalfa takes timely haying and planting, but both land and livestock will improve with your efforts.

Bruce Anderson
Extension Forage Specialist

If you don't need the grazing, make hay for young livestock by cutting when oats just begin to head out or increase yield by about one-third and cut oats in the milk stage for excellent stock cow hay. Another option is to plant a mixture of oats and Italian ryegrass. Oats comes on strong early while Italian ryegrass tends to wait until about June before it grows rapidly. Then it just keeps growing and growing high quality leaves the rest of the year as long as moisture is available.

For straight oats, drill at least three bushels per acre as soon as possible and oats will be 6 to 8 inches tall and ready to graze by early May. With good soil moisture and 40 to 60 pounds of nitrogen, oats can provide a couple months of grazing for one or two cows per acre. For extended grazing, drill only a couple bushels of oats plus around twenty pounds of Italian ryegrass per acre. Your stocking rate might need to be a little lighter at first, but with some timely moisture you can continue to get great grass all summer and fall.

Bruce Anderson
Extension Forage Specialist

USDA Nebraska Agricultural Statistics Service: Wheat condition rated 0% very poor, 2% poor, 38% fair, 48% good, and 12% excellent. This rating is above a month ago and well above the 36% good to excellent reported last year at this time. With soil temperatures above a year ago, greenup was evident in some southern fields.

Hay and forage supplies were mostly adequate statewide.

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