Posts Tagged ‘wheat diseases’

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.

Wheat Disease Update – June 11, 2010

Friday, June 11th, 2010

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

With the dry weather, wheat is beginning to turn in most area of the state. It looks like scab will not be an issue this year. Leaf rust and stripe rust did appear, late for the most part, but should have minimal effect on yield if the wheat was not sprayed.

Small Grain Disease Update

Friday, May 28th, 2010

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

After checking the state small grain variety trial at the REC near Georgetown I can report that there were several cultivars that had low levels of stripe rust and several with low levels of leaf rust. The recent wet weather may cause some localized outbreaks of stripe rust but it should be too late to cause much yield loss. All these infected areas were past flowering, mostly milk to soft dough stage, so it is too late for fungicide applications. There were low levels of speckled leaf blotch caused by Septoria tritici and low levels of tan spot as well as Stagnospora leaf and glume blotch. No head infections were seen last Friday. These too may increase with the wet weather early in the week.

Small Grain Disease Update – April 30, 2010

Thursday, April 29th, 2010

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

Keep scouting wheat for foliar diseases. Stripe rust is still a concern and is present in the South. Warmer weather will favor the Septoria, Stagnospora complex that causes speckled leafspot and glume blotch as well as common leaf rust and tan spot.

Last week I inadvertently did not include Twinline fungicide from BASF as another choice for powdery mildew control and other diseases on wheat and barley.

Agronomic Crop Diseases

Thursday, April 8th, 2010

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

Wheat
Wheat development is later than normal due to the adverse wet weather conditions beginning back in the fall. It is not too early to remind growers, consultants and fieldmen about several resources that are available for monitoring Fusarium head blight (scab). Two websites are available, the first is the scab predictor site http://www.wheatscab.psu.edu/ with the risk map tool and the second is a new site called Scab Smart.

Scab Smart Web Site Can Help With Head Scab Management
The U.S. Wheat and Barley Scab Initiative (UWBSI) has a Web site that provides farmers with information on how to manage Fusarium head blight, commonly known as scab.

Scab Smart is designed to serve as a quick guide to the integrated strategies that result in optimum reduction of scab and its primary associated mycotoxin, deoxynivalenol (DON).

On the site, producers can access information by management strategy or wheat class. Scab Smart’s content will be updated on an ongoing basis as new management information becomes available.

The site can be accessed through this website http://www.scabsmart.org

Stripe Rust and Leaf Rust
On another topic, stripe rust and to a lesser extent leaf rust, are increasing in the South. There have been reports of greater than normal infection levels of stripe rust in Louisiana, Texas and Oklahoma. It is never easy to predict if it will make it to Delmarva. Stripe rust has not been a problem in Delaware since 2006 and 2007. When it has occurred it has had variable effects on wheat depending how mature the crop is when the disease appears. Most of the damage in the past has occurred in the northern parts of the state. When scouting wheat later in the season keep this disease in mind. Alerts will be given if it gets closer to us. Generally applications with a triazole containing fungicide made at flag leaf emergence through heading will provide good control.


Stripe rust on wheat.

Corn
There have been growers with increasing southern root knot nematode populations in field and sweet corn, especially when pickling cucumbers, soybeans, and lima beans have been in a rotation. The best way to reduce root knot nematodes in corn is with an at-planting application of Counter 15G. The data I have seen for seed treatments that might be effective for root knot have not been consistent at this time. They are definitely worth looking at but how effective they will be is still a question in my mind.

Wheat Disease Update – July 3, 2009

Thursday, July 2nd, 2009

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

Scab
There have been reports of wheat being rejected at the elevator for excessive vomitoxin (DON) levels in the grain due to head scab infection. The following was written by Dr. Arv Gybauskas from the Univ. of Maryland about blending good grain with contaminated grain. “The question arises can you blend the infected seed lots with clean seed to avoid a complete loss of the harvested seed. Blending to dilute DON levels is very tricky. In the EU it is even illegal once the grain has left the farm and is tested by an elevator or mill. The problem is DON is not uniformly distributed in the seed and without testing and complete mixing of truck-loads of seed you could still end up with a load that could be rejected. In that case you would even have lost the good seed. A better solution, although not an easy one nor is it a guarantee to make the seed marketable, is to further clean out the seed and have it tested again.

To avoid getting into this jam next time, it will take a complete management program that includes rotation, selection of varieties that have some resistance and only recommended fungicides applied when needed. We will present data and more details on these choices as we finalize the results from research trials this season.”

Grain Testing for Vomitoxin (DON)
The Delaware Department of Agriculture is conducting testing for DON in grower submitted samples. Growers should submit a 2 lb sample in a plastic zip-lock bag to the DDA in Dover (2320 S. Dupont Highway, Dover DE 19901). The sample should be clearly labeled with your name, billing address and telephone number. The costs are:

Vomitoxin test = $40/sample (DDA will provide a certificate that certifies the testing procedure). If the grower or their insurance company requires a USDA/FIGIS grade certificate, they will need to locate a laboratory that has that certification.

Grain grade factors (e.g. moisture, test weight, damage) = $15/sample

The link below describes the exact ELISA test that DDA will be conducting: http://www.neogen.com/FoodSafety/pdf/ProdInfo/Page_24.pdf.

Any questions please call the DDA Seed Lab at (302) 698-4590.

How to Get a Good Representative Sample for Testing
The reliability of testing is greatly influenced by the sampling procedure. To achieve a more accurate DON level estimate, it is critical that the collected grain sample be representative of an entire truckload or bin of grain. Grain and other particles separate based on particle size and density as it flows into a truck or bin. Typically, the smaller, denser material is near the center and the larger, lighter material is near the outside of the container. Therefore, it is expected that there will be a variation in the concentration of affected kernels in various portions of a truckload. In addition, since DON levels can vary greatly between kernels of similar size and density, it is important to take several samples from various locations within the load. Probe samples should not be taken from the center or outer portions of a load because these areas do not reflect a cross section of the load. The samples also must represent spatially distinct areas of the load. The probe should collect the sample from as much of the entire depth of the truck as possible. Four to five probes per truck are recommended. To obtain an accurate sample from an end gate grain stream, samples from the entire width and depth of the grain stream should be collected, not just the first and last portion of the load. A Pelican sampler or other sampling device aids in proper sample collection. At least four samples of the entire grain stream should be collected at intervals to represent spatially different portions of the load. Information from NDSU fact sheet “DON (Vomitoxin) in Wheat: Questions and Answers” http://www.ag.ndsu.edu/pubs/plantsci/pests/pp1302.pdf.

Wheat Disease Update — June 26, 2009

Friday, June 26th, 2009

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

Wheat harvest has begun. I saw a few combines in the field on Wednesday, June 24. Grain quality may be an issue in some areas, especially if no fungicides were applied. Some sooty mold can be found on weather damaged wheat and barley. They are superficial dark fungi that discolor the heads but do little to reduce test weight or yield. That has already occurred before they infect the heads. Heading applications of fungicides, especially the strobilurins, will eliminate them or greatly reduce them – which also translates into good straw quality as well.

sootymoldSooty mold on wheat heads

Black “Sooty” Head Mold on Wheat and Barley

Friday, June 19th, 2009

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

Both barley that is still in the field and wheat that was not sprayed with fungicides are beginning to blacken in the field. The blackening of the heads is caused by several fungi that are referred to as “sooty molds”. Sooty mold fungi colonize wheat heads when wet, humid weather occurs during the latter stages of grain development and crop maturation. Molding is frequently most severe when harvest is delayed. In addition, heads that are shaded, weakened, undersized, or prematurely ripe are frequently affected by sooty molds. Head molding is also prevalent when plants are deficient in nutrients, lodged, or damaged by insects or other diseases. These molds are superficial and do not affect the grain directly or reduce test weight. This condition, although rough in appearance, does not significantly affect crop yield or test weight.

Wheat Disease Update – June 12, 2009

Friday, June 12th, 2009

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

Wheat is rapidly turning but scab is widespread in the state. We did not dodge the bullet unfortunately. Levels of scab really vary depending on the flowering time of the wheat and whether it corresponded with favorable weather for infection. We can expect lower yields and test weights were scab is heavy.

The first symptoms of Fusarium head blight include a tan or brown discoloration at the base of a floret within the spikelets of the head. As the infection progresses, the diseased spikelets become light tan or bleached in appearance. The infection may be limited to one spikelet, but if the fungus invades the rachis the entire head may develop symptoms of the disease. The base of the infected spikelets and portions of the rachis often develop a dark brown color. When weather conditions have been favorable for pathogen reproduction, the fungus may produce small orange clusters of spores or black reproductive structures called perithecia on the surface of the glumes. Infected kernels are often shriveled, white, and chalky in appearance. In some cases, the diseased kernels may develop a red or pink discoloration.

fusariumgrain 

Grain produced in heads damaged by Fusarium head blight is often shriveled, white, and chalky in appearance.

Fusarium graminearum is known to produce two important mycotoxins, deoxynivalenol (DON) and zearalenone, which can contaminate the diseased grain. The mycotoxin DON can cause reduced feed intake and lower weight gain in animals at levels as low as 1-3 ppm, especially in swine. Vomiting and feed refusal can occur when levels of DON exceed 10 ppm. Humans are also sensitive to DON, and the FDA has recommended that DON levels not exceed 1 ppm in human food. Ruminant animals, including dairy cows and beef cattle, are less sensitive to the toxin. The fungal toxin zearalenone has estrogenic properties and produces many reproductive disorders in animals. Swine are the most sensitive to the toxin, but cattle and sheep may also be affected. Zearalenone concentrations of 1-5 ppm can result in negative effects in animals and humans. Producers concerned about these mycotoxins should have grain tested prior to feeding to animals. Contact the state or local extension office for more information about testing for mycotoxins.

When high levels of Fusarium head blight are present in fields, precautions can be taken to reduce mycotoxin contaminations of the grain. The mycotoxin contamination is often highest in the severely diseased kernels. Adjusting the combine to blow out the small, shriveled kernels can help reduce mycotoxin levels. Harvested grain should be dried to 13.5 percent moisture as soon as possible to limit continued fungal growth. Grain suspected to have been damaged by Fusarium head blight should be tested for DON and zearalenone at a private agricultural lab or grain elevator. Do not mix contaminated grain with good grain prior to a mycotoxin analysis. The mixing will result in more contaminated grain, which may be difficult to sell.

Edited from Penn State fact sheet on Head Blight authored by Eric DeWolf. http://www.wheatscab.psu.edu/PDF/Fusarium_Head_Blight_.pdf

Leaf rust is present in varying amounts. In my estimation it has arrived too late to impact yield, but it can be seen on unsprayed wheat that is still green. Tan spot turned out to be the most prevalent foliage disease this year.

Corn and Wheat Disease Update – June 5, 2009

Friday, June 5th, 2009

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

Corn
No need for me to tell you how bad the weather has been so far for corn. Stands are still being reduced by excessively wet soils and the Pythium and Fusarium damping-off that is occurring as a result of the wet soils. Fungicide treated seed, good drainage and some warm temperatures would help considerably in getting the plants out of the ground and growing.

Wheat
Fusarium head blight or scab is being seen in some fields in Kent and Sussex counties. The occurrence and severity so far has been variable but, in general, I think we dodged a bullet this time. Our wheat for the most part was already in flower before the most favorable weather came for scab (Figure 1).

fusarium head blight 

Figure 1. Fusarium head blight or scab.

Take-all was diagnosed this week as well from two fields. Take-all is characterized by patches in the field that can vary in size but the wheat is generally stunted and the heads bleach out prematurely. Infected plants can be easily pulled out of the ground due to the extensive root rot that occurs. The other symptom is the dark streaking at the base of the stem (lowest node under the leaf sheaths), see Figure 2. Take-all can be controlled by rotating out of wheat for a year. However planting wheat followed by double crop soybeans followed by wheat is not an effective rotation for take-all control. Manganese levels also interact with take-all. Be sure that soil levels of manganese are adequate for the crop and check pH so that the managanese is available. High pH makes manganese unavailable.

takeall

Figure 2. Take-all symptoms on the lower nodes. Note lack of roots as well.

Tan spot (Figure 3) has been present for almost three weeks in wheat. This foliar disease can look like Septoria (Stagnospora) leaf and glume blotch. It is caused by the fungus Pyrenophora tritici-repentis.

 tanspot

Figure 3. Tan spot symptoms on wheat.

It has been widespread on Delmarva this season because of the amount of rainfall that we have had. It is too late for any control, but this disease is favored by wet, warm weather. Most of the spots are in the lower canopy and may reach the flag leaf before the plants begin to dry down. Applications of foliar fungicides at heading or earlier have been providing good control of this disease. At present most of the infection is in the lower canopy and the effect on yield should be minimal if the disease does not move up to the flag leaf or the leaf below the flag leaf.