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Volume 11, Number 2 - February 2005

This Month in Ag Connection

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Soybean Rust - Special Edition

It is difficult to predict the impact soybean rust will have on Missouri producers. Soybean rust has the potential to reduce yields significantly, to increase production costs and to reduce profits. Weather conditions that promote introduction of rust spores from the southern states into Missouri and weather conditions that favor development of the disease during the growing season will determine how severe soybean rust is each year.

Lessons learned from Brazil

Soybean rust arrived in Brazil in 2001, therefore much of what we know comes from Embrapa Soybean, Brazil’s National Center for Soybean Research. Because this is a new disease to the US, no one can predict how soybean rust will affect the US in the 2005 growing season. However, it is best to understand various factors that affect the occurrence and impact of soybean rust.

Asian soybean rust – Phakopsora pachyrhizi – is a fungus spread by wind blown spores. The disease causes plant defoliation, poor pod set and pod fill, and ultimately low yields. Initially rust infection occurred only after plants reached the flowering stage. Now infection is occurring earlier in plant development. Fungicide is the only known control option available. When untreated or treated too late, losses can exceed 80 percent.

It is easy to misdiagnose the disease. It is very important to accurately identify the disease early. Plants infected with the rust pathogen look similar to those infected with other pathogens that cause brown spot, bacterial blight, downy mildew and bacterial pustule. Start spraying fungicides as soon as the disease is identified. From the moment that a field is blanketed by rust spores to the appearance of spore-filled pustules on leaves is about 9 – 12 days. By day 25, any infected crop untreated with fungicide is beyond help.

Embrapa research has developed the following information on fungicide application. The efficiency of fungicidal application is closely related to sprayer technology. Farmers typically use between 15 to 20 gallons per acre when applying with spray booms and about 3 to 4 gallons per acre when applying from aerial sprayers. For most Brazilian Soybean fields, two fungicide applications were sufficient to control rust. In some cases, additional applications were necessary.

(Author: Wayne Crook, Agronomy Specialist)

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Soybean Rust Fungicides

Fungicides will be a new experience for most soybean farmers. Among the fungicides that are currently approved or that we anticipate being approved, there are four different chemical groups. Each group represents a different mode of action. The advantage of having four different modes of action is to lessen the possibility of resistance developing. If only one mode of action was available, then development of resistance would be more likely.

There are two basic types of fungicides:

Two other issues will be different with fungicides than with herbicides. For herbicides, it is critical to get a lethal dose on the weed but complete coverage is not that critical. With fungicides, good coverage of the soybean leaves that are present at the time of application is very important.

There will be issues about the droplet size and the ability of the spray to penetrate the canopy. The other critical issue in using fungicides against soybean rust is to get an application on when the disease first appears.

Fungicides With Full Federal Labels
-Chlorothalonil (protectant) -Bravo Weather Stik
-Echo 720
-Echo 90DF
-Azosystrobin (systemic) -Quadris
-Pyraclostrobin (systemic) -Headline

Fungicides With Approved Emergency Exemption Labels
-Propiconazole (systemic) -Tilt
-Propimax EC
-Tebuconazole (systemic) -Folicur
-Myclobutanil (systemic) -Laredo EC
-Laredo EW

Fungicides Submitted But Emergency Labels Not Yet Approved
Trifloxystrobin (systemic) Stratego (trifloxystrobin + propiconazole)
Tetraconazole (systemic) Domark

Be prepared for an update on sprayer technology and the development of an alert system in the future.

Detection soybean plots on the periphery of soybean fields provide good monitoring for early rust detection. The plots must be destroyed as soon as infection sets in to prevent further spread of rust spores.

(Author: Wayne Crook, Agronomy Specialist)

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Managing Soybeans To Reduce Soybean Rust Potential

Under the present situation and with the unknowns associated with what soybean rust will do in 2005, one sound approach is to produce the best crop that you can without making any major changes in management practices, except to increase your scouting techniques, watch for the disease, and be ready to spray. The following are practices that may be considered as more information is discovered.

Variety selection -- Currently no resistant or tolerant varieties are available and it may take at least 5 to 8 years for one to be developed.

Planting early -- Planting early could get the crop development further along before the rust hits and yield reductions would be smaller. This may reduce the impact of soybean rust but yield could be reduced with earlier planting.

Planting early maturity varieties -- The theory is to have the soybean plants further into seed filling when the rust arrives. Early maturing varieties are shorter, have fewer branches, smaller leaf areas, and probably yield less than maturity groups 3 and 4 in central Missouri.

Tillage -- The purpose of tillage for disease control would be to destroy over-wintering sites for fungus or to bury sources of spring inoculum. Rust fungus is not expected to overwinter in Missouri in most years. Crop residue will not be a source of inoculum in Missouri. Rust fungi can survive for long periods of time (over 60 days) on living plant material.

Rotation -- Reduce rust inoculum by decreasing the number of times soybeans are planted in rotation. Again, since rust will not overwinter in most years in Missouri, this will not have much of an effect. Rotating between corn and soybeans and reducing the soybean acreage may be site specific and depends on current soybean/corn mix, yield potentials and changes in input costs. At present prices, the economics indicate that with one fungicide spraying, soybeans are still a better economic choice. With two applications of spraying, it is a toss up economically between corn and soybeans.

(Author: Wayne Crook, Agronomy Specialist)

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Scouting Techniques

Field scouting for rust is more intensive than for insects or seedling diseases. Initially target fields that are planted early, fields with early maturing varieties, low lying fields, fields with early canopy closure or fields where morning moisture would linger longest. Target fields should switch over from once a week scouting to at least twice a week scouting beginning in June or with R1 stage of growth, sooner if confirmed reports are received of rust outbreaks in the southern states.

A minimum of 5 locations per field should be scouted or 1 spot-check per 5-8 acres in field larger than 40 acres. At each location check twenty feet of row, paying special attention to the lower leaves. Check both the upper and lower leaf surface for abnormal symptoms. Use a 10x to 20x hand lens to help detect rust pustules. If uncertain about identification of suspected diseased leaves, collect 20 leaflets with suspect symptoms and submit for diagnosis.

Use a random scouting pattern, with additional attention to locations in high moisture areas. For example, the west-side of hills, fence rows, woods and buildings or any part of the field where dew periods are prolonged.

(Author: Wayne Crook, Agronomy Specialist)

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Risk Management

The USDA Risk Management Agency (RMA) that oversees crop insurance states that "losses to soybean production due to soybean rust disease is an insurable cause of loss provided the insured can verify that the cause was natural and available control measures were properly applied... The RMA will be...vigilant to monitor when outbreaks are detected in an area to determine if an insured could have applied recommended fungicides in a timely manner and did not." It will be imperative for "producers to keep informed of soybean rust outbreaks in their area and take recommended measures to control or prevent the disease impact if an outbreak is anticipated or already in the area."

There are two major categories of crop insurance products for soybeans in Missouri. Yield insurance contains the familiar catastrophic plan, the actual production history plan and the group risk plan. All pay indemnities when yields are lower than a level chosen by the farmer purchasing the insurance. Revenue insurance contains crop revenue coverage and revenue assurance. These plans are more complex with indemnities being paid when either revenue or yields fall below a level chosen by the purchasing farmer.

Seventy-five percent of soybean acres in Missouri were insured in 2003. For the last five years Missouri farmers have received more than $2 from insurance indemnities for every $1 paid in premiums (Note: 2004 crop insurance data are not yet published but I do not think it will pay as well, given the yields and prices seen in 2004).

With so many farmers purchasing and benefiting from crop insurance, considering the impact of Asian soybean rust on their crop insurance decision seems wise. Should the policy purchased this year be the same as last or does the added risk of soybean rust losses argue for a change? The answer lies, in part, on what you expect the impact of soybean rust to be in your area and in the nation.

Historically the catastrophic plan pays poorly. Farmers who purchase this plan rarely receive an indemnity because the yield must fall below 50 percent of their 10 year average. If you believe, should soybean rust hit, it will devastate your crop, catastrophic insurance may be worthwhile. Be warned the RMA is expecting farmers to take recommended measures to protect their crop from soybean rust.

If you believe that soybean rust, should it hit, will impact your entire county, Group Risk Plan (GRP) may be useful. GRP is not often purchased and pays only when the county yield is below a certain level. GRP is a good plan for those whose farm yields closely follow county yields. It is less expensive than other forms of insurance but rarely pays.

Most farmers purchase revenue assurance (RA) rather than crop revenue coverage (CRC). CRC differs from RA in that CRC purchases benefit from higher harvest time prices should prices increase throughout the growing season. If you think that soybean rust will significantly reduce US soybean production increasing soybean prices, CRC would allow you to benefit from that price increase.

As always, crop insurance decisions should be made in consultation with your financial advisor. The major impact of soybean rust may be that it causes you to rethink your crop insurance choices rather than just take the same level of coverage that you have had for the last several years.

Any crop insurance decision for soybeans grown in 2005 must be made by March 15, 2005.

(Author: Ray Massey, Ag Extension, Social Sciences)

Statements the risk management agency has made:

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Web Sites For Soybean Rust

(Author: Don Day, Natural Resource Engineer)

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Introducing Rich Hoormann

Rich Hoormann is our new region agronomy specialist as of January 3rd. Rich comes to us from St. Peters, Missouri where he had been working as a consulting agronomist.

Prior to working as a consultant, Rich worked for Agriliance LLC and Farmland Industries as a technical agronomist covering the Midwest. Rich got his first agronomy experience by working for Nebraska Cooperative Extension in the sand hills region of the state. After spending three years with Nebraska, Rich took a position with the University of Missouri as an Extension Region Agronomy Specialist in the East Central Region, where he spent 12 years.

Rich has a farm background having been raised on farms in southern Illinois and eastern Missouri. Rich got his formal education from Southern Illinois University-Carbondale, majoring in Plant & Soil Science. Rich is in the Morgan County Extension Center at Versailles. His phone is 573-378-5358. Email is

(Author: Don Day, Natural Resource Engineer)

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Publishing Information

Ag Connection is published monthly for Central Missouri Region producers and is supported by University of Missouri Extension, the Commercial Agriculture program, the Missouri Agricultural Experiment Station and the MU College of Agriculture, Food and Natural Resources. Managing Editor: Kent Shannon.