Posts Tagged ‘soybean cyst nematode’

2009 Soybean Cyst Nematode Survey Results

Thursday, May 6th, 2010

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

The soybean cyst nematode (Heterodera glycines) is the most limiting biotic factor of soybean production in Delaware. In 1993 and 1994 a major effort was made to survey the soybean acreage for the soybean cyst nematode (SCN) and determine the race composition of the SCN populations present at the time. The Delaware Soybean Board funded this project and the results demonstrated that roughly 60% of the populations that were race tested were race 3 and 30% race 1 and the remainder a mix of races 5, 7, and 9. Since that time Round-Up Ready soybeans were introduced with a single source of resistance to SCN derived from a soybean plant introduction referred to as PI88788. At the time of the first survey we demonstrated a significant yield reduction in one variety trial where race 3 resistant soybeans were planted in a field known to be infested with race 1. This was the first indication that not all race 1 populations could be controlled with a race 3 or 3, 14 resistant soybean variety. For the past 10 years SCN has not been identified as causing much yield loss because symptoms that were seen previously, namely severe stunting and chlorosis, only seem to be present when a susceptible variety is grown or high egg numbers combined with dry weather at planting occurs when a resistant variety is planted. During the 2008 growing season a small number of soybean fields had stunted plants, chlorosis, and SCN was present on the roots. All of these fields were planted with a Round-Up Ready variety with resistance to SCN. The difference in 2008 was that it was dry from planting through the first thirty days after planting. High SCN egg numbers and dry weather early are known to be very detrimental to early soybean growth and can produce stunting, chlorosis and yield loss.

Within the last 5 years there were indications that race 3 is no longer the predominant race. A small set of samples tested here and those sent to other institutions have tested as race 1. Since the majority of resistance in Round-Up Ready soybeans is from PI88788, which allows varying amounts of reproduction of race 1 populations, these varieties may have reduced effectiveness in suppressing current SCN populations. Other control measures may be needed if the current population structure is no longer predominately race 3. No surveys of SCN had been conducted in Delaware since last survey in 1993 and 1994.

The results of the 2009 survey were very informative. No SCN were found in New Castle County even though the previously reported areas were sampled intentionally. In Kent county most of the infested fields were south of Dover. 41% of the samples in Kent County were infested. It was no surprise that all but one sample in Sussex County was infested, resulting in 96% of the samples taken in Sussex were infested. Fifteen samples (43% of the 35 samples that had SCN) were sent to the University of Missouri Extension Nematology Laboratory for race and HG typing. The most significant finding was that no race 3 populations were identified. Race 1 was the most prevalent (47%) followed by race 5 (33%) and two race 2 populations (20%). These results confirmed our suspicions that the race structure in DE has indeed shifted.

 

Mature cyst of the soybean cyst nematodes with 200-250 eggs.

Since more than 90% of the current soybean acreage infested with SCN in Delaware is planted with glyphosate resistant soybeans with SCN resistance from PI88788, it was significant that 100% of those SCN populations could reproduce on PI88788 from 40- 80% (average 67%) compared to a susceptible variety. Thirteen of the populations from the 1993-4 survey had an average female index (FI) on PI88788 of 24%. This means that the current SCN populations that we sampled will reproduce and increase on varieties with PI88788 as the source of resistance to SCN — although more slowly than on a susceptible variety. At what level they will produce on these current varieties depends on the population of SCN present. Will you notice any symptoms on the crop? It will depend on the growing season and the initial number of SCN eggs present in the field.

Managing SCN requires knowing if fields have SCN and how many eggs are present. Growers with increasing egg counts in fields planted with SCN resistant varieties will need to rotate to a non-host crop like corn or vegetables (except snap beans, which are also a host). Soil sampling in the fall after harvest is probably the best time to monitor SCN populations but samples can be taken anytime the soil is not flooded or frozen. When soybeans are grown, do not plant the same SCN resistant varieties in the same field, rotate varieties as well as crops. Although most varieties have resistance from PI88788, there are 4 major genes for resistance and several minor ones. Varieties with resistance from that source can vary in the resistance genes they carry. So there are differences between varieties that have the same source of resistance. Planting high yielding varieties with resistance to SCN when SCN egg counts are low to medium can be expected to perform well under our conditions. The problem is that the nematode populations can be increasing on some of these varieties depending on the SCN population in the field and the crop’s full yield potential may not be met.

Beat the Pest-Take the Test
Soil sampling is highly recommended if you are planting soybeans frequently. Irrigation can mask SCN damage so irrigated fields should be sampled as well to make sure that populations are not increasing.

A workshop on soybean cyst nematode is planned for August 3, 2010.

Agronomic Crop Diseases

Thursday, April 22nd, 2010

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

Wheat
The first disease of the season on wheat is usually powdery mildew. In general, powdery mildew has not been a problem for several years. Once wheat reaches jointing (Growth Stage 6) it should be scouted regularly for powdery mildew. As always, planting the highest yielding resistant varieties is the best control strategy, but if mildew threatens to rob yields later, fungicide control is the best control measure. Tilt, Propimax EC, Stratego, Quilt, Proline, and Caramba (the new Group 3 triazole from BASF) are suggested for control when and if fungicides are needed. These fungicides are also very effective for control of tan spot and Septoria leaf spot and glume blotch. It is common for powdery mildew to infect the lowest leaves and remain there for some time. The critical time to scout for powdery mildew is GS 8-10 (when the last leaf just appears until head emergence) to determine if fungicides are needed.

Barley
We have had reports of increasing amounts of powdery mildew on barley. ‘Thoroughbred’ looks to be the most susceptible variety but others should be scouted as well. Regionally we have no data to evaluate fungicides for control of barley diseases because barley rarely needs to be sprayed for diseases and the cost has been prohibitive. Times have changed, and if the heads are emerging and the top two leaves are infected there may be some benefit to controlling powdery mildew on a susceptible variety such as ‘Thoroughbred’ if the weather continues to favor powdery mildew. Stratego, Tilt, Quilt (10.5 – 14.0 oz/A) would be suggested for control if necessary. A beneficial non-target effect will be brighter straw if straw is being baled.

Powdery mildew on barley.

Soybean Cyst Nematode
It is still not too late to check for soybean cyst nematode, especially if susceptible soybeans are going to be planted. Soil test bags with the submission form can be purchased at the Extension offices. If you have a fax machine and need results quickly, test results can be sent via FAX if you provide the number on the Nematode Assay Information Sheet. This information sheet can be found on the web at the Plant Clinic Website http://ag.udel.edu/plantclinic .

Agronomic Crop Disease Update

Thursday, March 25th, 2010

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

Wheat
It has been a tough year for wheat production. The wet fall delayed planting, then large areas have been inundated with water for long periods of time and there has been grazing by geese. Areas of the state where wheat has survived but under very wet conditions may be at risk from Pythium root rot if wet conditions persist. The other threat, as if there wasn’t enough trouble for wheat, is from the fungal transmitted soilborne viruses, wheat soilborne mosaic virus and wheat spindle streak mosaic virus (WSSMV). Wet soils in the fall following planting can result in severe infections of wheat soilborne mosaic virus that appear as irregular stunted areas in low areas of the field. Mild stunting and yellow green mottling, dashes and streaks on the leaves are diagnostic for WSSMV. There are no controls for either disease for the present crop. Resistant varieties for both diseases are available.

Soybean Cyst Nematode Survey
I am waiting on the results of the last two soil samples before presenting the results of the Delaware Soybean Board sponsored survey for SCN in Delaware. The results so far have confirmed a shift of the race composition in Delaware soybean fields and the nasty nematode has not gone away.

Soybean Disease Update

Friday, September 18th, 2009

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

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 www.sbrusa.net.

sbrmap17Sep09

Soybean Cyst Nematode Diagnosed in Soybean and Snap Bean

Thursday, July 2nd, 2009

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

SCN was diagnosed this past week in soybeans and snapbeans. These two hosts are the only crops that are affected in the region. If you see stunting and yellowing, carefully dig up the affected plants with a shovel or trowel and gently shake the soil from the roots. White or yellow females will be seen attached to the infected roots if present. They are small, much smaller than the nitrogen fixing nodules, but can be seen with the naked eye. A 10x hand lens makes the task much easier to see the lemon shaped females. Don’t presume that all the stunting that can be seen is due to water-logged soils or compaction. If it is not clear what the problem is or if cysts cannot be seen, a soil sample of the affected area can be taken and checked for SCN or other nematodes. Test bags and more information is available at the County Extension offices and forms and info at the Plant Diagnostic Lab site at http://ag.udel.edu/extension/pdc/pdf/Nematode_Assay_taking_samples.pdf.

soybean cyst nematode

Still Time to Test for Soybean Cyst Nematode

Friday, May 1st, 2009

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

It is still not too late to check for soybean cyst nematode, especially if susceptible soybeans are going to be planted. Soil test bags with the submission form can be purchased at the Extension offices. If you have a fax machine and need results quickly, test results can be sent via FAX if you provide the number on the Nematode Assay Information Sheet. This information sheet can be found on the web at the Plant Clinic Website http://ag.udel.edu/extension/pdc/index.htm.

Soybean Cyst Nematode Survey to be Conducted in 2009

Friday, March 27th, 2009

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

The soybean cyst nematode (SCN) is the most limiting biotic factor of soybean production in Delaware. In the mid 1990s a major effort was made to survey the soybean acreage for SCN and determine the race composition of the SCN populations present at the time. The Delaware Soybean Board funded this project and the results demonstrated that roughly 60% of the populations tested were race 3, 30% were race 1 and the remainder were a mix of races 5, 7, and 9. Since that time Round-Up Ready soybeans were introduced with a single source of resistance to SCN derived from a soybean plant introduction referred to as PI88788. At the time of the first survey we demonstrated a significant yield reduction in one variety trial where race 3 resistant soybeans were planted in a field known to be infested with race 1. This was the first indication that not all race 1 populations could be controlled with a race 3 or 3,14 resistant soybean variety. For the past 10, years SCN has not been identified as causing much yield loss because symptoms that were seen previously, namely severe stunting and chlorosis, now only seem to be present when a susceptible variety is grown. This past season a small number of fields had stunted soybeans, chlorosis, and soybean cyst nematode was present on the roots. All of these fields were planted with a Round-Up Ready variety with resistance to SCN. The difference last season is that it was dry from planting through the first 30 days. High SCN egg numbers and early dry weather are known to be very detrimental to early soybean growth and can produce stunting, chlorosis and yield loss. It is time to determine what SCN egg numbers are present in soybean fields 12 years after the initial survey was conducted and what the race composition of infested fields might be. Within the last 5 years there are indications that race 3 is no longer the predominant race. A small set of samples tested here and those sent to other institutions have tested as race 1. Since the majority of resistance in Round-Up Ready soybeans is from PI88788, which allows reproduction of race 1 populations, these varieties may have reduced effectiveness in suppressing current SCN populations. Other control measures may be needed if the current population structure is no longer predominately race 3. No surveys of SCN have been conducted in Delaware since 1996.

The Delaware Soybean Board approved the SCN Survey Project that will provide this valuable information. We are asking that soybean growers that have had SCN in the past or that have soybean fields that have not been producing as expected to have your field sampled for SCN. The field can be in a crop presently as long as we can take a sample in a zig-zag pattern. Fields that have been in continuous soybean production or rotated with corn or other crops are good candidates for the survey. Sampling fields this spring before any tillage is done will give us a good start on the project, which will continue into the fall as well. If we find SCN infested fields during the growing season, these will be added also. We are hoping to sample at least 30 fields in Sussex, 20 in Kent and 10 in New Castle. A percentage of the fields will be typed for race, or HG type as we call it now. If you are interested in participating in the survey please give me a call (302) 831-4865 or email bobmul@udel.edu or contact your county agent and we will take the sample.

Soybean Disease Update

Friday, July 11th, 2008

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

Soybean Cyst Nematodes
The first soybean cyst nematode sample came into the lab this week. Plants were stunted and in some patches dying. White and yellow females were very evident on the infested roots. High initial egg populations in the soil and droughty conditions soon after planting can result in these symptoms. Other problems can look like SCN. The only way to be sure is to look at the roots or take a soil sample that includes some plants as well.

 

SCN damage often shows up as random spots in the field.

 

Stunted and dying plants infested with SCN

Soybean Rust
A few more counties in Florida have been added to the map this week. Both finds were soybean rust infecting kudzu. The disease is still moving slowly down South. Be sure to keep up-to-date on the latest info by visiting www.sbrusa.net or http://sbr.ipmpipe.org

Test or Scout for Soybean Cyst Nematode

Friday, June 20th, 2008

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

Soybean cyst nematode can be seen on plants that are 32-35 days from planting. The recent dry weather can accentuate the damage from SCN. Look for areas in the field which are yellow and/or stunted. The small yellow or white cysts can be seen easily at this time if you have a 10X hand lens and carefully dig up the plants and do not pull them from the soil. Soil sampling is also encouraged if you do not find the cysts or to confirm their presence if you are not sure. Soil sample bags are available from the county Extension offices. Remember, if soybeans are being planted after barley and wheat it still is not too late to soil test for SCN, especially if you are not planting a resistant variety.

 

Small white female SCN and a large nitrogen fixing nodule for comparison. (SON)