Posts Tagged ‘soybean cyst nematode’

Nitrogen Fertilization and Irrigated Soybean Production

Friday, August 24th, 2012

Richard Taylor, Extension Agronomist; rtaylor@udel.edu

A number of people have been asking about applying nitrogen (N) fertilizer to irrigated soybeans so I thought I would make a few comments about the practice in case they might help you in making the decision as to whether to spend the money in hopes of getting a yield response.

To begin with, I have tried this practice on both full-season and double-cropped soybeans at one time or another. I’ve tried applications of N at both 25 and 50 lbs N/acre at R2 (full flower) and R4 (full pod) and for double-cropped soybean I’ve tried these rates broadcast at planting. I never got a significant response to the treatments although for double-cropped soybeans I was close to seeing an increase in early plant height and pod set. For yield, the treatments were all within a bushel or two of each other.

That being said, I should point out that significant responses have sometimes been reported from down South but only when the N was applied through an irrigation system (for the reports I’ve seen) and when both boron (B) and N were applied in combination. At the time of the research that I conducted, we did not have the capability to apply N to my plots through the irrigation system. I had to apply the N with a back-pack CO2 sprayer while walking through the soybeans. I did have the studies irrigated immediately after applying the treatments to minimize the chance of foliar burn. I remember hearing from the southern researchers that they felt that the leaf damage caused by walking on N or applying N with a ground rig would negate the slight yield response that they were able to obtain using fertigation. I also did not apply B along with the N which may have also reduced the chances of obtaining a positive yield response since B is important in sugar transport and in helping flower set.

I understand that some people suggesting that N should be applied to irrigated soybeans are suggesting the inclusion of sulfur (S) (probably as ammonium sulfate) along with the N. This makes some sense from a biological point-of-view in that the plant requires enough S to make the S-containing amino acids required for protein synthesis. However by the time soybeans reach the full bloom or full pod stage, the root system has reached or will soon reach its deepest penetration of the soil. Even the sandy soils in Sussex County, Delaware, were found to have large quantities of S (typically 300 to 500 lbs S/acre) stored in the clay lenses found in the 1 to 2 foot depth of soil and soybean roots should be able to tap into this S reserve by reproductive stage.

Let me summarize below some of my thoughts on trying to increase soybean yields with N fertilizer.

● If soybeans already have matured to the full seed stage (R6) where a full size seed is found in a pod at one of the four upper most nodes with a fully expanded leaf, it is much too late for N application to increase yield potential in my opinion. All the research that I’ve seen involves the application of N at full bloom (R2) to full pod (R4) stage.

● I doubt that the addition of S as ammonium sulfate is going to increase your chance of obtaining any return on your investment since soybeans are very likely to have more than an adequate supply of S available by this time of year due to root growth. An exception would be where there is a root restricting compaction layer in the top 12 inches of soil but in this case the chance that fertilizer will improve yield is very low.

● If your expected yield potential is not at least 60 to 70 bushels/acre, N fertilization will not help. Next year, try using either the liquid seed Bradyrhizobia inoculants or some of the new graphite soybean inoculants since the new strains available can really help increase your yield potential.

● If you still plan to apply N fertilizer to your soybean crop, be sure to add about 0.5 pound of boron per acre. The data I’ve seen where a yield response was obtained with late season (R2 or R4) N application were always where B had been included with the N.

● I would suggest limiting any N application to no more than 30 lb N/acre since levels higher than this have often been shown to reduce the nitrogen fixing activity of the soybean nodules. If this occurs, you’ll be trading dollars essentially since the nodules will either stop N fixation or reduce fixation to a degree where the plant will need the N you apply just to produce the original crop’s yield potential. Some studies with early season manure applications have shown yield reductions because the crop ran out of N during the reproductive stages and had to reinitiate nodulation because the crop ran out of available N.

● Do not consider N applications on non-irrigated soybeans. Keep in mind that in the case of a dryland soybean crop, the overall limiting factor is water availability not nutrient availability.

● Also if your field has a history of soybean cyst nematode (SCN) infestations, do not add N fertilizer since SCN will be your yield limiting factor not N or S or B fertilizer.

Nematode Sampling for Soybean

Friday, March 2nd, 2012

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

This is not a good time to take nematode samples for root-knot nematode detection but if soybean cyst nematode (SCN) is a concern and you are planting soybeans this spring it is not too late to sample. SCN is detectable all season long as long as the ground is not frozen or flooded. Remember that snap beans are also a host of SCN and fields planted to snap beans should be checked for SCN. Lima beans are resistant to SCN. Testing most of the major baby lima bean cultivars confirmed that they are resistant to the major race or genotype of SCN that is prevalent in Delaware.

Nematode sample bags are available at all the county Extension offices as well as the information sheet which needs to accompany each sample. This info is also available online at http://ag.udel.edu/extension/pdc/. Samples do not have to be submitted in these bags but are there for your convenience. Soil samples for nematode detection should be at least 2 cups of soil placed in a Ziploc plastic bag. Do not use paper bags unless they are double-bagged with a plastic bag.

Soybean Disease Update – September 23, 2011

Friday, September 23rd, 2011

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

Soybean Vein Necrosis Virus
I just wanted to add a brief summary for our WCU readers that soybean vein necrosis virus has been seen in all three counties in Delaware and apparently is widespread in the surrounding states of PA, MD, and VA. We see it everywhere we look now but I am not sure how much effect it is having on yield at this point. Researchers in other parts of the country are also working on it and have a few more years experience with it. It is premature to say too much about it other than we now know what is causing the symptoms we have seen this year and probably last year as well, but did not know what it was. By the time the winter meetings occur hopefully I will be able to share more hard facts about the disease and control options for our region.

Early symptoms of soybean vein necrosis virus (SVNV) from DE

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 and information sheets are available from the county Extension offices for $10/ sample bag.

Soybean Rust Risk Assessment (ZedX, Inc. & PSU)
Despite recent heavy rainfall along the Atlantic Coast and throughout the Northeast from the remnants of Lee and Hurricane Irene, source inoculum in the Southeast was likely still too low to cause widespread transport and deposition of spores further north. Soybean rust was, however, identified in extreme southwestern Georgia for the first time this season. Due to the ongoing drought in Texas and Oklahoma, the slow progression this season in the Southeast, and the fact that the primary soybean production season is in the later stages, it is unlikely that soybean rust will spread as far as it has in years past. As such, the risk area will remain rather minimal in spacial coverage (see map below). Double crop soybeans along the Gulf Coast could still be at risk for soybean rust as the season progresses, but even double cropped soybeans are at a minimal risk.

The above image displays the current threat level of soybean rust. The yellow “wait” areas are considered slightly at risk, orange “watch” areas are at moderate risk, and red “warn” areas are at great risk or already identified positive for soybean rust. Risk areas are estimated based on meteorological factors affecting spore transport and deposition and factors conducive for further development within the canopy such as temperature and moisture. Biological factors such as host plant and crop phenology are also considered. Risk assessment maps are produced by the PSU Ensemble Field Crop Rust Forecasting Program.

Soybean Vein Necrosis Virus Confirmed in DE, MD and VA

Friday, September 16th, 2011

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

Soybean vein necrosis virus was confirmed this week by Dr. Yannis Tzanetakis, Department of Plant Pathology at the University of Arkansas. So the symptoms that we have been seeing and sharing with concerned growers are due to this new virus disease. Although I say it is new, some of the first symptoms were seen in 2008 in Tennessee and Arkansas. The subsequent work by the researchers at Arkansas discovered the new virus. They were able to report that this new virus disease, soybean vein necrosis virus (SVNV), belongs to a group of thrips-transmitted viruses. This group called the tospo viruses includes several that we see in greenhouse production in the region and in the field occasionally, namely tomato spotted wilt virus and impatiens necrotic spot virus.

 Early symptoms of soybean vein necrosis virus (SVNV) from DE

This group of viruses are acquired by thrips feeding on infected plants and once acquired then the virus can be transmitted by the thrips for the rest of its life. We call this a persistent virus in the vector and this may allow us to control SVNV by controlling thrips. This is very preliminary and much work is being done in the Midwest to identify the thrips vectors and possible other hosts of the virus that may harbor it and allow thrips feeding to move it to soybeans. It is too early to know if that strategy will work practically. The question we all have is: will it reduce yield here or affect seed quality? So far I have not seen enough leaf loss to imply that some yield effects are possible. But we have some time to go before maturity, so the jury is still out on the yield effects here in the Mid-Atlantic. Fortunately this group of viruses is not known to be seed-transmitted and that is being addressed by these researchers.

The researchers from Arkansas have noted that often a single virus infection may not have much of an effect but multiple infections with other viruses may increase yield loss potential. We have occasional outbreaks of bean pod mottle virus and we have seen soybean mosaic virus and peanut stunt virus in soybeans in the region, so the potential is here for multiple infections. We do not have much information about the extent of other virus diseases in soybeans.

The other avenue of control is identifying sources of resistance and evaluating current soybean varieties for resistance. Ideally identifying sources of genetic resistance that are incorporated into good varieties will be best control strategy. That work is ongoing as well. It is too early to be making recommendations but growers need to be aware of this disease and know that work is being conducted to answer some of these pressing questions.

Also, 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.

Agronomic Crop Disease Update – July 8, 2011

Friday, July 8th, 2011

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

Soybeans
Now is the time to start checking soybeans for soybean cyst nematode. Once soybeans have reached the 3rd trifoliate leave stage (roughly about 28-32 days from planting) the white or yellow female cysts can be seen on the roots. If you see irregular patches of stunted soybeans don’t presume the stunting is from drought. Digging the plants carefully may reveal SCN is present and could be the cause of the stunting. If you are seeing many cysts and stunting on resistant soybeans it is time to rotate out of that field to reduce SCN egg numbers.

White and yellow female soybean cyst nematodes on roots, 34 days after planting

Corn
Three corn samples arrived in the plant clinic this week with bacterial stalk rot. If you are irrigating from surface water sources, such as ponds or ditches, there is a risk of bacterial stalk rot. The bacterial can be in the irrigation water and get trapped in the whorl, the ear leaf sheath, and the ear shank. These places provide a place for water to sit and the bacteria can enter the stalks and cause a soft decay of leaf sheath, stalk, and ear shanks. It is foul smelling as well. It appears as random infected plants in the field and as a result it does not cause major losses. Corn is thought to be susceptible for a short period of time and the older the corn the less likely infection will occur. There is no chemical control for bacterial stalk rot. Treating irrigation water in the system with hypochlorite is an alternative solution.

Bacterial stalk rot

 

Agronomic Crop Disease Updates

Friday, June 3rd, 2011

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

Soybeans
The dry conditions combined with high soybean cyst nematode (SCN) egg counts could mean we will see more stunting from SCN this season. Be on the lookout for stunting in irregular areas. The SCN females can be seen on the roots of infected soybeans around 28-32 days after planting.

Barley
Barley harvest is fast approaching and the crop looks pretty good. Besides some leaf rust, net blotch, powdery mildew on ‘Thoroughbred’, and a little head scab, diseases have not been bad this season.

Wheat
A few diseases were observed during a recent check of the variety plots near Middletown in New Castle County. Low levels of tan spot and powdery mildew were seen in a few varieties, but all but one of the 45 entries had some head scab. Most of the infections were under 1% of the heads infected and many of those heads were only partially infected. Wheat in NCC was the most at risk according to the scab predictions. Some shriveled grain with the white coating of the Fusarium fungus was observed on some of the infected heads. Increasing fan speed on the combine will blow the light chaffy “tombstones” out the back and not contaminate the rest. Planting multiple wheat varieties with different flowering times (maturity) will decrease the risk of scab for next year. Statewide, overall scab levels are low compared to several years ago. I had mentioned in last week’s WCU that several varieties in the variety trial had genetic flecking or a resistance reaction including Merl, USG 3209, USG 3251, USG3665, Sunburst, and Grow Mark FS627. These symptoms are not an active disease.

Flecking on USG3409 that looks like a disease

Head scab on wheat

Healthy kernels and Fusarium head scab infected “tombstones”

Tan spot on wheat

 

Harvesting Grain from Scabby Fields
The following are tips to reduce the amount of scabby kernels in the harvested grain and to avoid potential health problems for combine operators and grain handlers. Scabby grain is contaminated with mycotoxins, especially vomitoxin, which is harmful to humans.

Harvest tips:
1. Avoid breathing in dust from scabby fields by using a high quality dust mask. Spores of the scab fungus (Fusarium graminearum) and small pieces of contaminated plant parts are present in the dust. Inhaling these particles may cause health problems.

2. Harvest the most severely scab damaged areas, such as low areas or double seeded headlands, separately. Don’t co-mingle the most damaged grain with sounder grain.

3. Turn up the air on the combine to blow out the lightest, scabby kernels back into the field.

4. If rain is forecast, it may be better to harvest scabby fields at slightly higher moisture content than to wait for grain to dry down. However, this grain still needs to be dried down and maintained below 15% moisture after harvest to prevent fungal growth in storage.

5. After harvest, gravity table grain separation can be used in removing more of the light-weight, scabby kernels.

6. Get grain from scabby fields tested for vomitoxin before feeding, before blending, or before making a decision to discard suspect grain.

From http://www.scabsmart.org/harvest%20practices.html

 

News from the Nematode Assay Service

Friday, April 1st, 2011

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

There is a new sample submission form available on the Plant Clinic website http://ag.udel.edu/plantclinic. This new form is updated to reflect personnel changes and lines for entering email addresses and information that will help us respond as quickly as possible. Please fill out a sample submission form each time you submit samples. These are also available from the county Extension offices when you purchase the soil bags for nematode analysis.

Agronomic Crop Disease Updates – September 17, 2010

Friday, September 17th, 2010

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

Corn
Corn harvest is underway so be sure to check corn fields for lodging potential by squeezing the lower nodes or pushing on the stalks. A simple way to do this is to walk through the field and, keeping your hands at chest height, push stalks 8-10 inches from vertical. If 10-15% of the stalks lodge, schedule the field for early harvest before a strong wind results in severe lodging. Drought conditions during grain fill put substantial stress on corn plants. In many fields, it is likely that the corn crop responded by cannibalizing stalk reserves to fill the grain. This results in a weakened stalk and greater susceptibility to stalk rot.

Small Grain
Be sure that you plant wheat varieties with high levels of disease resistance. Select varieties with high levels of resistance to powdery mildew, leaf rust and stripe rust. Seed should be treated with Baytan, Raxil, Dividend or other labeled product to protect plants from loose smut and common bunt. Varieties that are susceptible to powdery mildew should be treated with Baytan, Dividend or other seed treatment that will protect them from early infection.

Soybeans
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 Rust Update
Nothing new has developed north of the North Carolina find on August 30. Florida had its first soybean rust detection on soybeans on September 14. Needless to say, soybean rust is not going to be an issue in most of the US this season.

Fall Nematode Sampling

Friday, September 10th, 2010

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

The fall is generally the best time to sample for nematode populations in vegetables and field crops. After harvest is complete but before any fall tillage is the best time for taking survey samples. With the very dry conditions, however, I would delay taking fall nematode samples until we get some rain. Samples taken from very dry soil may not be representative of what is present in the field.

One other observation is that nematode soil samples should not represent any more than 20 acres. Nematodes are not uniformly distributed in the soil and it would be easy to miss significant numbers if a single sample of 20 soil cores represented a large acreage. I am not trying to generate more work, just better information on which to make an informed recommendation.

Soybean Disease Update – July 2, 2010

Friday, July 2nd, 2010

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

Soybean Cyst Nematode
SCN was diagnosed this week on soybeans. 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. If it is not clear what the problem is or 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 are 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 . We will be having a Soybean Cyst Nematode Workshop on August 3. See the meeting announcements for more information and registration forms.

 

Septoria Brown Spot
Septoria brown spot has not been as prevalent as last year but it has been seen in a few fields so far. It is one of the earliest fungal diseases that we see and can be found on the unifoliate leaves and the lower trifoliate leaves when it is present. Badly infected unifoliate leaves will usually fall from the plant and we will not see this disease again until the soybeans canopy and conditions would be favorable for infection. Most seasons this disease is not yield limiting.

 

Septoria brown spot on unifoliate leaves of soybean