Soybean rust — where from here?

In November 2004, soybean production in the continental United States was forever changed when soybean rust was detected for the first time near Baton Rouge, La. Initial response statements suggested that the fungus that causes the disease was carried into the United States on Hurricane Ivan.

Historically speaking, prior to 2001, soybean rust had not been detected outside of the Eastern Hemisphere until it was reported in Paraguay during the 2001 season. Following that report, the disease moved through South America’s soybean producing areas quickly and was detected in the United States within three years.

Since 2004, soybean rust has been detected in 20 states. However, reports of extensive yield loss have not been reported in Mississippi or many of the other states that have detected soybean rust to date, except for an extremely isolated number of cases that have occurred in Alabama, Georgia, and Louisiana.

Over the past four years of scouting, we have learned a few things about soybean rust. Not only are we better at scouting for soybean rust at the field level, but we are positive that we have more soybean rust in the Mid-South today than we did four years ago. Additionally, soybean rust has tended to be detected later in the growing season, in regards to both calendar date and soybean growth stage, which has resulted in extremely low (if any) yield losses.

Published reports in 2005 estimated that on average, annual yield loss of 10 percent would be expected in almost all U.S. soybean-producing areas with as much as 50 percent yield loss in the Mississippi Delta, Mid-South, and other southeastern coastal states. However, these large yield loss estimates have been unrealized to date.

Collective yield losses in Mississippi over the past four seasons have been zero bushels specifically attributed to soybean rust. While this is a historical perspective on the disease from the Mississippi production area, this is not to suggest that yield losses will not occur in the future.

Although some fungicides have been applied in response to soybean rust detection in Mississippi, as a whole the overall number of acres that have received a fungicide following a county going “red” on the public Web site (, formerly has been extremely low in comparison to the state’s total acreage.

We make this statement with a simple purpose. We must not become complacent when it comes to the future threat from soybean rust.

This is even more important to consider when we reflect on the disease as it occurred in 2008. In Mississippi, a total of 79 counties were identified as containing either kudzu (three counties) or soybeans (76 counties) infected with soybean rust. This was a 300 percent increase in the number of counties reported as soybean rust positive when compared with 2007.

Chronologically, from the first identification in the Delta on Sept. 6, within three weeks the disease was detected in every Delta county. Over a period of three days, soybean rust was detected across a geographic area that stretched from Mars Hill, Miss., in Amite County, to Cub Lake, Miss., in DeSoto County; an approximate distance of 250 miles from south to north. Seven counties (Amite, Claiborne, DeSoto, Lincoln, Madison, Tate, and Tunica) were identified as containing soybean rust between Sept. 22 and Sept. 27.

The vast majority of the detections occurred in soybeans that were beyond growth stages where rust could have produced a damaging situation or triggered a fungicide application — generally considered to be R5.7. However, with the vast geographic area from where rust was detected, we cannot stress how important it is to not become complacent regarding the potential threat from this disease.

There is one important thing to note with the majority of the rust that we detected in Mississippi soybean fields in 2008. With the exception of a few locations in 2008, rust was detected at extremely low levels in late (post R5.7 soybeans). However, two specific fields had a heavy infection (two fields in particular in Sharkey County, Miss.), one with a fairly heavy infection at R5.8 and the other with an extremely heavy level of infection detected at R7.

As an interesting aside to this situation, there were several fields within the vicinity of these two particular fields at the R5 growth stage where soybean rust was not detected. In general, most of the fields where we detected rust in 2008 between R7 and R8 had very few leaves, and we tend to choose these fields to determine if the fungus is present within a particular county.

We will likely have a potential annual threat from soybean rust as long as we continue to grow soybeans in the Mid-South. Don’t be alarmed — we can effectively manage soybean rust if and when the threat could become real.

Sentinel plots have been used since 2005, and prior to 2008, soybean rust had always been detected on soybeans in a sentinel plot before commercial fields in Mississippi.

While almost 70 percent of Mississippi’s commercial soybean acres were planted in the Delta in 2008, soybeans were grown in 76 counties throughout the state. In addition, Mississippi has approximately 250,000 acres of kudzu. With 82 counties in the state, 80 counties are known to contain kudzu (based on scouting data collected over the past four years). Issaquena and Sharkey counties appear to be the only two without kudzu.

However, one of the biggest problems with monitoring kudzu for the presence of soybean rust is there are patches of kudzu resistant to and susceptible to infection from the fungus. Without scouting every kudzu patch, it is difficult to determine which locations are susceptible and have been infected in the past.

Most states in the southeastern United States have a “historically” infected kudzu location. These historically infected kudzu locations have become infected with soybean rust every year since 2004-05, usually by a certain date.

Alabama, Florida, Georgia, and Louisiana all have kudzu patches that have been found to be soybean rust positive for the past three, if not four, continuous years. In Mississippi, 42 kudzu locations have been identified as susceptible to the fungus over the past four years, but it was not until 2008 that two kudzu locations were found to be soybean rust positive two years in a row.

There are several things that we need to consider as we move forward in a “soybean rust world.”

• While it is possible that rust could cause severe yield losses, there is the potential (and a very real one at that) that we might never see yield losses that equal the initial estimates. However, it goes without saying, we can’t get complacent about this disease. The last four years are a good indication of what we can expect for 2009 and beyond. We will find soybean rust in Mississippi, it is only a question of where and when.

• Several agronomic issues contributed to what seems to have been a greater amount of rust on commercial soybeans in the 2008 Mississippi crop. Soybeans were planted a good bit later due to the weather conditions in the spring and the high number of wheat acres — we had approximately 400,000 acres of doublecrop soybeans. In addition, corn was planted later and many producers had to finish planting corn before they could get their soybeans in the ground. Producers, in some areas of the state also had to replant soybeans, due to a poor initial stand or spring floods.

Additionally, Mississippi normally plants approximately 70 percent Maturity Group 4 soybeans with the remainder being MG 5 soybeans. However, in 2008 we were approximately 50-50 MG 4 and MG 5 soybeans, and in some areas there were low numbers of acres planted with MG 6 soybeans (planted due to a shortage of available seed).

• Add in the six weeks of cooler-than-normal wet weather that we encountered during August and September and excellent conditions occurred for soybean rust to develop.

• Mississippi has one of the earliest-planted soybean crops in the United States. Early-planted soybeans and a production system tends to plant MG 4 soybeans (prior to 2008) may have been a reason we have avoided yield loss from soybean rust since the disease has normally been detected in September and October.

If we continue to have an early-planted, MG 4 soybean crop in Mississippi, we will likely limit the late-season soybean rust pressure.

Current funding situation

As of Dec. 31, 2008, federal funding for sentinel plot monitoring ended. Initially the sentinel monitoring program was funded by the USDA-Risk Management Association (RMA). Following the initial detection of rust in Louisiana in November 2004, a rapid, national response was necessary.

USDA-RMA funded the program in part because it was widely believed there would be insurance claims for losses from soybean rust. The USDA-RMA has traditionally funded “new and emerging” situations.

Since rust is no longer “new and emerging” and there hasn’t been a large number of insurance claims due to soybean rust losses, USDA-RMA dropped funding for sentinel plot monitoring.

However, funding has been provided for 2009 through the USDA for the maintenance of the IPM-PIPE Web site ( that has presented information on the presence of soybean rust since 2005. There is one caveat regarding this situation: none of the money provided (approximately $750,000) can be used for scouting or sentinel plot monitoring. The money is only available for maintaining the Web site and continued communications.

In addition to that funding situation, the North Central Soybean Research Program and the United Soybean Board have funded 25 states (approximately $360,000) that are loosely considered Tier 2 (Arkansas, Iowa, Illinois, Indiana, Kansas, Kentucky, Missouri, North Carolina, Nebraska, Ohio, Oklahoma, South Carolina, Tennessee, and Virginia) and Tier 3 (Delaware, Maryland, Michigan, Minnesota, New Jersey, North Dakota, New York, Pennsylvania, South Dakota, Wisconsin, and West Virginia) states by the soybean rust state coordinators.

To be more specific, none of the above money will be distributed to the Tier 1 states of Alabama, Florida, Georgia, Louisiana, Mississippi, and Texas for 2009, even though over the past four seasons these states have accounted for 59.6 percent (674 positive counties out of a possible 1,142 total positive counties) of all of the positive soybean rust detections.

Tier 2 states have accounted for 41 percent of the positive identifications in four years while Tier 3 states have had only one positive county in that time.

Southern Tier 1 states (except Mississippi) didn’t require additional funds and will be able to operate this year using funds from 2008. Mississippi will conduct the sentinel plot monitoring program with funds remaining from 2008, but since Mississippi runs a robust scouting program, the remaining 2008 funds would not be sufficient. Therefore, the Mississippi Soybean Promotion Board has provided additional support for the 2009 season.

Moreover, it is likely that the entire monitoring program will be back to square one at the end of the 2009 season and have limited funding available. Most of this will depend on the course the disease takes during 2009.

With regards to Mississippi, we plan to run the exact same soybean rust monitoring program as we have in the past. We aren’t going to change a thing just yet because our producers know how important it is to be aware of the potential threat from soybean rust.

The soybean rust telephone hotline (866-641-1847) — in collaboration with Arkansas, and Louisiana and paid for by BASF and the Mississippi Soybean Promotion Board — will continue and will be updated with pertinent information regarding soybean rust.

Additionally, there is a weekly recorded radio program regarding the soybean rust situation in Mississippi. The radio update is also funded with check-off dollars.

Tom Allen is an Assistant Extension/Research Professor, Delta Research and Extension Center, Stoneville, Miss. Billy Moore is Professor Emeritus, Mississippi State University. Trey Koger is Soybean Extension Specialist, Delta Research and Extension Center, Stoneville, Miss.

TAGS: Soybeans
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