Posts Tagged ‘soybean rust’

Soybean Rust Update

Thursday, April 15th, 2010

Bob Mulrooney, Extension Plant Pathologist;

The cold winter extended deep into the South, and kudzu was killed back in most sites and is only now re-growing in Florida and the other Gulf States. No soybean rust has been observed on kudzu at this time. Soybean sentinel monitoring sites are being planted at this time in FL, MS, LA, and AL.

Funding for the ipmPIPE sentinel plots was reduced for this season and only the states in the South are receiving funds to continue the sentinel plots. Tier 3 states which include DE were not funded this year. I will be establishing one sentinel plot at the REC near Georgetown, DE. With our past history, the presence of scouting to our south and the availability of soybean information on the ipmPIPE website, I think we will be able to respond in a timely fashion if rust should become a threat in 2010. If the situation should change later in the season, soybean production fields can and will be monitored as part of my Extension responsibilities.

Just to clarify, the Soybean Rust ipmPIPE website will continue to operate and information for the US will continue to be posted for everyone to see. Delaware will be posting information on the national site for our growers as well as communicating to you through Weekly Crop Update. We will be operating one soybean sentinel plot in 2010. The soybean aphid monitoring program is being retired and will not be available in 2010.

Soybean Disease Update

Friday, September 18th, 2009

Bob Mulrooney, Extension Plant Pathologist;

Soybean Cyst Nematode
Do not ignore soybean cyst nematode. Soil sampling after harvest before any fall tillage is recommended for fields to be planted next season to soybeans following this year’s crop. Do not plant SCN susceptible varieties without soil testing first. Soil sample bags are available from the county Extension offices for $10/sample bag.

Soybean Cyst Nematode Survey
As soybean harvest begins we will be contacting growers to see if they want to participate in this needed survey to assess SCN numbers in fields. The last survey was in the mid-90s. If you have a field with a history of soybean production and want to have the field included please contact me at 302-831-4865 or contact your county agent.

Soybean Rust Update
On September 16, soybean rust was reported in Coffee, Crisp and Irwin counties, Georgia; Coffee and Tipton counties, Tennessee; Barbour, Chambers, Cherokee, DeKalb and Henry counties, Alabama; and Warren County, Kentucky. On September 15, soybean rust was reported in Yell County; Arkansas; Laurens County, Georgia; and Lauderdale, Leake, Newton, and Winston counties in Mississippi. On September 14, soybean rust was reported in Craighead, Jackson, and Lawrence counties, Arkansas; Calhoun County, Florida; St. James and St. Tammany parishes, Louisiana. As the soybean crop matures, more soybean rust reports are expected north of the current distribution.

Rust continues to increase along the Mississippi most of these new detections are on soybeans that will not likely be impacted by rust this late in the season. Sampling continues in Delaware and will until October. The risk of rust is low for us unless some hurricane or tropical storm develops that brings spores north. The latest wet weather systems have been southerly so no transport in our direction. Except for a few coastal counties, the Carolinas have been dry, which has limited spore production that could come our way. Keep abreast of the situation by checking the national ipmPIPE website at


Soybean Disease Update – September 11, 2009

Friday, September 11th, 2009

Bob Mulrooney, Extension Plant Pathologist;

Bacterial blight
has been diagnosed from several fields in the state as well as several of our soybean rust sentinel plots. This is another disease that we rarely see except when we have wetter and cooler temperatures than normal. At first the lesions or spots can look like Septoria brown spot but these are more angular with a yellow halo around the irregularly shaped necrotic spot. Young infected leaves are often distorted (see picture below). In most situations in Delaware, yield losses would not be expected from the levels of infection that I have seen. The bacteria survive on plant residue and seeds. Plowing to bury the plant residue would be suggested.

bacterial blight on soybeanBacterial blight on young soybean leaves.

Soybean Rust Update
On September 9, soybean rust was reported in Effingham, Jeff Davies, and Randolph counties, Georgia; Clay, Shelby, Tuscaloosa and St. Clair counties, Alabama; and in Evangeline, Ouachita, Rapides, Richland, and St. Landry parishes in Louisiana. On September 8, soybean rust was reported in five Mississippi counties (Choctaw, Clay, Monroe, Oktibbeha, and Webster). On September 6, soybean rust was reported in Wilkinson, Jefferson, Adams and Claiborne counties, Mississippi; and Pickens county, Alabama. On September 5, rust was observed in several fields in Shelby county in the southwest corner of Tennessee.

Soybean rust has been increasing in the Mississippi River Valley and has reached TN. It is also assumed that it is present in the whole coastal plane of GA at the present time. There is still little risk at the present time of rust appearing on Delmarva for some time. Most full season soybeans in the state are at R5 or later maturity and once they reach R6 they are no longer at risk from soybean rust. Double crop beans will be more at risk if the weather should bring rust spores north in the next few weeks. There is no need to spray fungicides on soybeans for soybean rust.


Soybean Disease Update

Friday, September 4th, 2009

Bob Mulrooney, Extension Plant Pathologist;

Powdery mildew is present on some varieties. It is not a yield limiting disease and control is not warranted. See the article in WCU 17:23 for more information on this disease. Downy mildew on soybeans is very common on varieties with no or limited resistance. It too is not thought to be yield limiting here. A few growers have asked about white mold in soybeans. This disease is caused by Sclerotinia sclerotiorum, the same fungus that causes white mold in snap beans, lima beans and peas. Soybeans that are rotated with these crops in fields that have had the disease in the past are most at risk. This disease occurs sporadically in Delaware. Conditions favoring white mold are usually present when we have had lots of rain and the temperatures are moderate during flowering. Crops that are lush and dense with tight canopies are most at risk since the lower parts of the plant stay wet for long periods of time. During dry seasons, growers that over-irrigate soybeans during the late flowering to early pod fill have induced it on fields with a history of white mold. The fungicides that are used on soybeans for disease control and plant health are not effective for white mold. Fungicide applications have not been very successful at controlling white mold.

Sudden death syndrome (SDS) was confirmed from the two finds last week from New Castle and Sussex counties. Several more fields have been diagnosed this week. We have not seen this disease in Delaware since 2000 when it was first identified. The reason we are seeing it again is that we had weather conditions that were very favorable for SDS, just like in 2000. It has to be cooler and wetter than normal for us in the early part of the season for SDS to appear. What does SDS look like in the field? Yellow blotches form between the veins, usually developing first on the uppermost leaves. In a few days the yellow blotches will coalesce and begin to turn brown. The end stage is complete tissue death between the veins, with the only green tissue remaining being that associated with the primary leaf veins. The edges of severely diseased leaves will roll inward. Over time, the diseased leaflets may fall off the leaf stalks (petioles) or they may remain attached to the plant. When you dig up the infected plants primary, secondary and tertiary roots are severely rotted. Nitrogen-fixing nodules are mushy. The exterior of the stem appears healthy but the interior of the stem is a milky-brown to gray color, compared to the yellow-white color of a healthy stem. Serious yield loss usually only occurs when plants are exhibiting serious foliar symptoms BEFORE mid-pod fill. After that time, plants can look pretty rough, but yields may not be affected much. Individual and groups of plants, 10-50 feet in radius, usually show a range of symptoms ranging from some leaf spotting to complete defoliation. Wet or otherwise stressed areas of fields from compaction or other causes, such as along field edges, will usually be the first to develop symptoms. In extreme cases, entire fields may show symptoms. When SDS is severe, symptoms will first develop in “hot spots” and later progress into other areas. This gives the effect that the disease is spreading, but in reality it is not. Rather the time of infection, crop health, and field conditions vary, so disease symptoms are expressed at varying times and rates.

Control of SDS
The only control is reducing plant stress by reducing compaction, and planting resistant or tolerant varieties. Rotation is of little to no value in controlling SDS. Be careful to check plants carefully for these symptoms because stem canker can also produce similar symptoms. The following pictures will give you a good idea of what SDS looks like in the field:

field shot of soybeans with SDSField shot showing the browning leaves and some defoliation

early leaf symptoms of SDSEarly leaf symptoms

later leaf symptoms of SDSLater leaf symptoms showing interveinal necrosis

SDS causes leaves but not petioles to fall off the plantLeaves will fall off but the petioles (leaf stalks) remain attached

stem of healthy soybean (lower) and soybean with SDS (upper)The bark has been removed from the lower stem and tap root to show the brown discoloration of the vascular tissue under the bark of the diseased soybean compared to the healthy white stem on the bottom plant.

Soybean Rust Report
On September 2, soybean rust was reported on soybean from a sentinel plot in Dorchester County, South Carolina just 30 miles from the Atlantic Ocean. This area has received abundant rainfall recently while the rest of the state has been dry. The amount of rust at this site is very low at the present time. On September 1, soybean rust was reported on soybeans in Jefferson and Phillips Counties, Arkansas; Panola County, Mississippi; and Macon and Miller Counties, Georgia. The disease was also observed in soybean sentinel plots in Lee and Macon Counties, Alabama, as well as on kudzu in Crenshaw County in that state. On August 29, soybean rust was detected on kudzu in Jackson County, Florida. On August 28, soybean rust was reported in Drew, Lincoln, Desha and Lee counties in Arkansas; Lafayette, Morehouse and West Carroll parishes in Louisiana; Attala, De Soto and Madison counties in Mississippi; and in Greene County, Alabama.

The total number of counties reporting soybean rust in 2009 has more than doubled the number that had reported rust on the same date in 2008. Rust is moving in areas that have had both the moisture and temperatures that favor rust in the South. Monitoring will continue here in Delaware. Many Group 3 and 4 soybeans planted in mid to late May are approaching R6 or later and would not be at risk if SBR would move north in a tropical storm event. Late double crop soybeans will be the most at risk if the weather pattern should change and we get some tropical storms or a hurricane. Most of the rust activity is in the Mississippi River Valley heading north into Arkansas. Besides the scattered reports of SDS, powdery mildew and downy mildew soybeans look good from a plant disease perspective.


Soybean Disease Update – August 21, 2009

Friday, August 21st, 2009

Bob Mulrooney, Extension Plant Pathologist;

Powdery Mildew on Soybeans
We received a report of powdery mildew on soybeans from Sussex County this week. The weather has been very favorable for powdery mildew on many crops, as well as ornamental plants of all kinds. Powdery mildew on soybean is a rare occurrence these days. It is caused by the fungus Microsphaera difusa and produces the white talcum-like growth on the leaf surfaces which can infect all the plant parts eventually. Symptoms can vary from one cultivar to another. Rusty spots, chlorosis, green islands, defoliation or combinations of these symptoms may occur. Most cultivars have the dominant gene for resistance to this disease. Fungicides are not recommended for this disease since it is not known to reduce yields.

powdery mildew on soybeanpowdery mildew on soybeanPowdery mildew on soybeans

Soybean Rust Report
On August 19, soybean rust was reported on soybeans in Bolivar, Issaquena, Sharkey and Warren Counties in Mississippi. On August 18, soybean rust was reported in commercial soybean fields in West Baton Rouge, Pointe Coupee and East Carroll Parishes in Louisiana. On August 15, soybean rust was reported in nine new counties in Mississippi, all in commercial soybean fields. The positive counties include Carroll, Grenada, Humphreys, Leflore, Montgomery, Sunflower, Yalobusha, Yazoo and Washington.

In spite of the rash of SBR finds in Mississippi most of these are at low levels and most soybeans are at R5 and later, so the threat from soybean rust for these growers is low. Earlier soybeans at R3/R4 would be at risk in these areas. Rust is heating up a bit in the South and may become more of a threat if spores are spread in the developing cold front that is forecast to bring rain to the region during the next several days. Spore deposition is forecast from the Gulf Coast through Arkansas and spreading as far north as Kentucky.

Soybean sampling for soybean rust continues here in Delaware. The only diseases that we are seeing in the sentinel plots are low levels of Septoria brown spot, downy mildew and Phyllosticta leafspot. Visit for more information.


Soybean Rust Update

Friday, August 14th, 2009

Bob Mulrooney, Extension Plant Pathologist;

On August 13, soybean rust was reported in Suwannee County, Florida on kudzu. On August 12, soybean rust was reported in three additional Florida counties, Duval, Madison, and Washington. On August 11, soybean rust was reported on soybean in Tift County in Georgia. On August 10, soybean rust was found for the first time this year in Arkansas, in Chicot County on soybeans. On August 6, soybean rust was found in Holmes County, Mississippi in a commercial soybean field; this is a first find in the state this year.

As you can see soybean rust activity is increasing in the South. Most of the spore movement is going toward the Mississippi River Valley and not east. There has been some spraying for soybean diseases in the South other than rust but the rust that has appeared in commercial fields has come too late to affect yields for the most part. The season is still young and we have considerable acreage of late soybeans this year, so time will tell. Soybean rust monitoring in Delaware has begun and we will keep you up to date.


Soybean Disease Update – July 31, 2009

Friday, July 31st, 2009

Bob Mulrooney, Extension Plant Pathologist;

Septoria brown spot and downy mildew continue to be the most common diseases seen at the present time. In areas that have had little rainfall and spider mite injury is present be on the lookout for Alternaria and Phyllosticta leafspot on stressed soybeans. Both fungi are weakly parasitic but infect drought stressed and mite infested soybeans.

alternaria leafspot on soybean

Alternaria leafspot on mite infested soybean leaf

Soybean Rust
On July 28, soybean rust was found in Assumption Parish, Louisiana, in a soybean sentinel plot. Soybean rust scouting continues in the U.S. and Mexico. In 2009, soybean rust has been found in five states and 32 counties in United States, and in two states and five municipalities in Mexico. There is no active soybean rust in Mexico at the present time.


Soybean Disease Update – July 24, 2009

Friday, July 24th, 2009

Bob Mulrooney, Extension Plant Pathologist;

Soybean Rust Update
On July 21, soybean rust was reported on kudzu from Escambia County in far west Florida. This site has been positive in previous years. On July 20, soybean rust was reported from Avoyelles Parish, Louisiana on soybean. On July 10, soybean rust was reported on kudzu in Columbia County, Florida. Soybean rust scouting continues in the U.S. and Mexico. Soybean rust scouting in DE will begin in August.


Downy Mildew
Downy mildew in soybeans is now being seen. Soybean downy mildew is caused by the fungus, Peronospora manshurica which only infects soybeans. The fungus causes irregular yellow spots on the upper leaf surface and a tuft of gray fungus growth on the corresponding lower leaf surface. Varieties vary in their level of resistance to this fungus. As best we know here downy mildew rarely, if ever, affects yield. In heavy infections seeds can become infected and have a coating of the reproductive structures of the fungus (oospores) over them. Fungicides are not recommended.

soybeandownymildewDowny mildew on soybean

Soybean Rust Update – July 10, 2009

Friday, July 10th, 2009

Bob Mulrooney, Extension Plant Pathologist;

Soybean rust was found on soybean for the first time in a Florida sentinel plot in Gadsden County in the panhandle. Rust is developing in kudzu sites in the other positive counties in Florida. Some areas have been very hot and wet others have been hot with no rain. Rust is developing slowly so far.


Soybean Disease Update — June 26, 2009

Friday, June 26th, 2009

Bob Mulrooney, Extension Plant Pathologist;

Septoria brown spot has been favored by all this wet weather and is easily found on the unifoliate leaves and the lower trifoliate leaves in most areas. These will usually fall from the plant and if it dries out we will not see this disease again until the soybeans canopy and conditions again would be favorable for infection. Most seasons this disease is not yield limiting. Spots seen this week were small but very numerous in one variety trial that I checked. septoriabrownspotSeptoria brown spot on unifoliate leaves of soybean

Soybean Rust Update
Soybean rust was reported in Geneva, Covington and Conecuh counties in south-central Alabama on kudzu on June 24. The disease was found at very low levels at each site which included two seperate kudzu patches in Covington County. On June 22, soybean rust was reported in a soybean sentinel plot in Acadia Parish in Louisiana. Soybean rust scouting continues in the U.S. and Mexico. The current conditions in the South are not going to be very favorable for rust development due to high temperatures.