Posts Tagged ‘fusarium head blight of wheat’

Small Grain Disease Updates – May 11, 2012

Friday, May 11th, 2012

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

Stripe rust in wheat has been seen in both DE and MD this week. The outbreaks at this time are small and for most of the state wheat is past flowering, so the impact of increased rust development at this time should be minimal. Anyone who applied a fungicide such as Tilt, Prosaro, or Caramba at boot stage or heading will have 2-3 weeks of control, depending when it was applied and when stripe rust spores arrived from the south of us. We have not seen stripe rust in our region for several years. There have been population changes in the rust and it may be more aggressive than what we have seen in the past. We would be interested to know if you see it and what varieties get infected and the severity of the infection. Initially it might be found in a small area or several small areas but if the continued rain and cooler temperatures prevail it could spread quickly. If the wheat is past flowering, check fungicide labels for timing. See the next article for more information on stripe rust and effect on yield as well as fungicide choices.

 Close-up of stripe rust symptoms showing rust pustules in a line or stripe.

 Stripe rust on wheat.

Several more wheat samples were confirmed with Barley yellow dwarf virus. Most of the symptoms are mild but very widespread when it is found in a field. There is little impact on yield as best we know, but there is still much to learn about this virus in this region.

 Barley yellow dwarf showing reddening of flag leaf.

Wheat Disease Update
The following was written by Arv Grybauskas, Extension Plant Pathologist, University of Maryland and adapted for Delaware by Bob Mulrooney, Extension Plant Pathologist, University of Delaware

The risk of scab development this season has been very low and most of our wheat will be scab‐free or, at worst, have infection levels well below 10%. Vomitoxin levels should therefore be well below the 2 ppm threshold for acceptance at mills for most of the crop. The last few days, however, indicate that there are a couple of regions in the state that might still develop some scab. Much of the wheat in the hot spots in eastern Sussex County should be past flowering, and therefore past the label growth stage limitation for treatment with fungicides. However, there may be late planted fields or later developing varieties that can be treated. Leaf rust has been present on susceptible varieties since early spring but has been kept in check by unfavorable temperature or moisture conditions. It still has the potential to develop and spread if temperatures warm into the 80s at daytime and drop only to the mid‐60s at night as long as showers continue or dew and RH is high. Treatment of susceptible varieties may be warranted if leaf rust is present and is threatening to reach the flag leaves.

Stripe rust has also made an appearance this season. It was just confirmed in Dorchester and Caroline Counties in Maryland as well as in Delaware on Monday, May 7. These outbreaks are in small pockets (foci) in fields and their appearance is consistent with long‐distance spore transport from either NC or KY on storm fronts that came through about 2 weeks ago. Stripe rust, unlike leaf rust, requires cooler temperatures. In fact, at temperatures above 77°F lesions will stop producing spores and secondary spread is reduced, and at temperatures above 85°F the pathogen dies. The question now is, what is the potential damage and do I need to apply a fungicide? The short answer is, in my opinion, the worst‐case scenario for either rust disease (susceptible variety, and continuous disease favorable conditions through grain‐fill, and a focus of rust is present in the field now) would potentially produce a 10% yield loss. Realistically the weather will probably be less favorable sometime during grain fill so losses are more likely in the 1‐7% range (Table 1). For either rust disease it takes 7‐14 days to go through an infection cycle (infections giving rise to more spores that cause new infections) under ideal conditions. With that in mind, by the end of the grain‐fill period it is possible that the plants will look nasty (100% of the plants with 40 to 65% flag leaf severity) but between hard and soft dough stages this typically only produces 1 to 7% yield losses.

Table 1. Approximate Yield Loss in Relation to Severity of Rust on the Flag Leaf at Various Stages of Growth

Growth Stage Flag Leaf Area Infected with Rust
10% 25% 40% 65% 100%
Flowering 10 15 20 30 35
Milk 2 5 8 14 20
Soft dough 1 3 4 7 10
Hard dough 1 1 1 3 5

From: Hunger, B. and K. Jackson. Foliar Fungicides and Wheat Production in Oklahoma.

At this stage the only products that can be considered are triazole fungicides. The products registered for scab management, Prosaro and Caramba, are also effective against leaf and stripe rust. Rust susceptible wheat varieties that are still eligible for a fungicide application (pre‐ or just at flower) that are not at risk of developing scab may be sprayed with Folicur or a properly labeled generic tebuconazole product for rust control. Note that Prosaro, Caramba and Folicur have a 30 day Pre‐Harvest Interval as well as the growth stage restriction. Tilt has a 45 day PHI, and therefore would only be an option on earlier stage wheat where the risk of scab was low.

Wheat Disease Update – April 27, 2012

Thursday, April 26th, 2012

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

BYDMV
We have had several more reports and a sample of Barley yellow dwarf mosaic virus in wheat. Irregular patches of varying height reductions, yellowing and purple flag leaves indicate BYDMV infection. Since this virus is aphid transmitted there are no controls at this time.

Fusarium Head Blight
With the much needed rain that came and the forecast for more Thursday and possibly Saturday as well some have been asking about the possibility of head blight or scab appearing. The forecast at the present time is the probability is low. The corn residue on the surface needs to be wet for a long time before spores are produced that can infect the wheat at flowering and the temperatures need to be in the mid-70s for significant infection to occur. The temperatures have been and are too low now for infection. As long as the wheat flowers between now and next Wednesday when the forecast is for warmer temperatures the wheat will no longer be in a susceptible stage of development for scab to infect. I think the risk of scab it very low and specific sprays for scab control are unwarranted at this time.

Keep up to date with scab by visiting the website and using the 2012 Predictor. http://www.wheatscab.psu.edu/ This will be important if we should get more rain later in the week.  Make sure the predictor says 2012 across the banner. For some reason my browser is going back to the 2011 site. If you run into the same problem here is the 2012 link http://www.wheatscab.psu.edu/riskTool_2012.html

Leaf Rust & Stripe Rust
More of a possibility is the occurrence of some late season leaf rust and stripe rust. There has been stripe rust reported in NC earlier in the week and now a report of leaf rust and stripe rust from Mt. Holly, VA in university test plots. These reports are fairly close and after a big rain event like we had with some more possibly on the way we may see some develop within the next two weeks. If growers have a variety that is susceptible to leaf rust or stripe rust, there is a chance that we could see more rust two weeks from now depending on the temperatures. Again that might justify application of a fungicide at flowering if you have rust present now or are growing a susceptible variety. With the lack of water there may be undetected leaf rust in the lower canopy and with the recent rain there could be spread to the upper canopy. Be sure to get out and check the wheat before making a spray decision. Prosaro plus a non-ionic surfactant can be applied to wheat until 30 days before harvest; for scab control it needs to be applied at early flowering in 5 gal/A if applied by air. Tilt can only be applied until full head emergence. With the low risk of scab, strobilurin fungicides such as Headline and Quadris could also be considered for protection against leaf and stripe rust as well as tan spot, and the Septoria complex if those diseases are present, which have not been seen because of the dry weather. Be sure to check labels for application restrictions. Our past experience has shown that diseases that appear late (after flowering) usually do not have time to infect the upper leaves that are important for grain fill and reduce yield. If diseases are present in the canopy at flowering there is more of a risk of diseases reducing yield and/or quality of the grain.

Some information from Dr. Christina Cowger from USDA at NC State Unversity indicates that the following varieties are susceptible to stripe rust and might warrant spraying especially if any rust is present now. There are some gaps in our knowledge about susceptibility to stripe rust, so this is a very limited list of known susceptibility for varieties that are grown in the Mid-Atlantic:

Coker 9436, DG Shirley, NC Cape Fear, NC Neuse, NC Yadkin, P26R12, SS520, SS560, USG3209, USG3592, USG3665, SS8404

Freeze Injury
We just received a wheat sample from Kent County, DE with random bleached awns as well as tips of some heads. If you see some irregular bleaching of heads don’t panic about scab. We suspect at this point since no fungus appears to be present on this sample that the damage is from freezing. From spike emergence through flowering, freezing can cause symptoms that range from minimal bleaching of the awns to severe grain yield loss, depending on the duration and degree of freezing.(See Photo 3 in the article by Richard Taylor, “Another Risk of Frost on the Small Grain Crop”, which is in this issue of WCU) If normal kernel development does not occur, then freeze injury can be suspected.

Small Grain Disease Update

Thursday, April 12th, 2012

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

The dry weather and low humidity has been very unfavorable for diseases at the present time. There are still some fields of barley with powdery mildew and leaf rust. If they needed treatments they should have been treated by now. Wheat is looking a bit better in that powdery mildew levels are low and except for some barley yellow dwarf mosaic virus in some areas the crop looks good. Rainfall is desperately needed. The risk for Fusarium head blight or scab is low at the present time. To keep track of the threat of scab be sure to check the website http://www.wheatscab.psu.edu/.

Head Scab and the Relationship to Saved Seed and Vomitoxin Production

Friday, June 10th, 2011

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

Head scab has been observed in barley and wheat this season in varying amounts. Barley is just now arriving at the grain elevators. The amount of scab that occurs is dependent on the flowering time, the presence of the scab spores that infect the heads during flowering and the weather conditions during flowering. Most of the barley and wheat varieties that we grow have little or no resistance to head scab. The fungus can be present on old corn stover, and residues of old barley and wheat crops. What drives this disease is wet, warm weather during the flowering period. If the heads of barley or wheat are infected with the fungus (Fusarium graminearum) that cause head scab, that fungus can produce several toxins that can contaminate the grain. These toxins are often referred to as vomitoxins because they can cause feed refusal in non-ruminant animals. The most common vomitoxin that is produced by the head scab fungus is deoxynivalenol or DON for short. DON production by the fungus is extremely variable depending on environmental conditions. The presence of scab on the grain does not mean that the grain has to have DON nor does high or low levels of scab relate to the amount of DON present. A high level of scabby kernels in the harvested grain means that DON will likely be present.

What about the saving or using seed from scab infected fields? As much scabby wheat kernels as possible should be removed from good seed during combining and seed cleaning. This is not easily done with barley or may not be possible because barley does not get as light as wheat. Saved seed kernels can be infected with Fusarium, and seed treatments can reduce the effects of Fusarium on seed. Fusarium on seed can cause a seedling blight of barley and wheat but the seedling infections do not result in head scab or DON in fields that might be planted with infected seed. In fact some studies have shown a reduction of scab infections in seed during storage. Low levels of scab infected wheat or barley can be saved for seed if properly handled and treated without any risk of scab occurring in the crop from that seed.

Another issue for barley producers is that the threshold levels of DON in wheat may not be the same compared to barley presuming that the barley is not intended for human consumption. The DON threshold for wheat is 1 ppm because of human consumption concerns. Barley for feed can have up to 10 ppm without harmful effects depending on the animals being fed and the proportion of infected grain being fed. In my opinion barley should not be held to the same threshold as wheat depending on its destination or final use. See the following information on DON levels in food and feed.

What are the critical levels of DON for use in food and feed?
The concentrations of DON in grain are expressed as parts per million (ppm). One ppm is equivalent to 1 pound in 1 million pounds, 1 penny in $10,000, 1 minute in two years, or 1 wheat kernel in 80 pounds of wheat. The U.S. Food and Drug Administration (FDA) has established DON advisory levels to provide safe food and feed. Unlike aflatoxin in corn, DON is not a known carcinogen. Furthermore, grain with DON would have to be ingested in very high amounts to pose a health risk to humans, but it can affect flavors in foods and processing performance. Human food products are restricted to a 1-ppm level established by the FDA. This level is considered safe for human consumption. The food industry often sets standards that are more restrictive. DON causes feed refusal and poor weight gain in some livestock if fed above the advisory levels. FDA advisory levels are as follows:

1 ppm: Finished wheat products, such as flour, bran and germ that potentially may be consumed by humans. The FDA does not set an advisory level for raw grain intended for milling because normal manufacturing practices and additional technology available to millers can substantially reduce DON levels in the finished wheat product. However, individual millers or food industries may have stricter requirements than 1 ppm.

10 ppm: Grains and byproducts destined for ruminating beef and feedlot cattle older than 4 months and for poultry, providing that these ingredients don’t exceed 50 percent of the diet.

5 ppm: Grains and grain byproducts destined for swine, providing that these ingredients don’t exceed 20 percent of the diet.

5 ppm: Grains and grain byproducts destined for all other animals, providing that these ingredients don’t exceed 40 percent of the diet.

Taken from NDSU Fact sheet PP-1302, DON (Vomitoxin) in Wheat. http://www.ag.ndsu.edu/pubs/plantsci/pests/pp1302.pdf

 

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

 

Small Grain Disease Update – May 27, 2011

Friday, May 27th, 2011

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

Barley
The most prevalent diseases that can still be seen in areas where the barley has not returned yet are the spot blotch form of net blotch and powdery mildew. After checking the barley varieties today near Sandtown in western Kent County I don’t believe that net blotch will be affecting yields, but powdery mildew on unsprayed ‘Thoroughbred’ will reduce yields if the flag leaf is infected. There is some scab infected barley in Kent County.

Wheat
The wheat in the Kent County variety trial has tan spot moving in rapidly on some varieties. Most of the varieties are in the watery ripe stage of development and will not likely be adversely affected. Leaf rust was easily seen on a public variety ‘Rumor’. Powdery mildew in general was low in most varieties but was in the upper canopy on SS8302, Milton, Bravo, and USG3770. There is a low level of scab in the trial as well. If scab is going to appear it should be evident now or very soon depending on location. Low levels of scab (less than 1% of the heads infected and most of the infected heads were only partially infected) were present in 8 out of 45 varieties (around 18%).There is some sort of physiological spotting that could look like a disease but is probably a resistance reaction by the variety in response to a fungal infection. This spotting was evident on the following varieties at this Sandtown location: Merl, Sunburst,USG3665, USG3409, USG3251, and Grow Mark FS627.

 

Small Grain Disease Update – May 20, 2011

Friday, May 20th, 2011

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

Fusarium Head Blight (Scab) in Wheat Update: Although the recent weather pattern early this week has been favorable for head scab in wheat, most of the wheat in Sussex and Kent County has completed flowering by now and not likely to become infected with scab. If you have wheat that is flowering now consider a fungicide application of Caramba or Prosaro. Wheat that is about 5 days or more past initial flowering cannot be treated. The labels state the last stage of application is mid-flower and there is a 30-day to harvest restriction.

Scab identified on barley. We just received a sample of ‘Nomini’ barley from Kent County and have confirmed a scab (Fusarium head blight) infection on the top 6-7 kernels. The sample was only two heads and several plants but growers will want to keep an eye out for bleached heads on barley from here on out. Nothing can be done now but increasing fan speed on the combine at harvest which can help blow the lighter chaffy infected grains out of the combine. Hopefully this turns out to be an isolated find.

 

Small Grain Disease Update – May 6, 2011

Friday, May 6th, 2011

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

Wheat
Be sure to keep scouting for the presence of diseases, especially powdery mildew, at this time. With the return of cooler temperatures and risk of showers and cloudy weather as well, powdery mildew could become a problem, especially in very thick stands of susceptible wheat. It is important to keep the uppermost two leaves as free of diseases as possible to protect yields. At the most, you can wait until you see 5-10% of the upper two leaves infected before applying a fungicide. Tilt, Stratego, Twinline, and Quilt can be applied as late as heads emerged but not yet flowering. If scab should be a concern this year it may be best to use only a triazole fungicide at heading through flowering to avoid mycotoxin issues if scab infection occurs. There is evidence that if fungicides containing strobilurins (Quilt, Twinline, Stratego) or strobilurins alone are applied during heading up to flowering, they can increase mycotoxin production if scab occurs during flowering. If a fungicide is needed as late as flowering for powdery mildew, Septoria leaf blotch, tan spot, or other disease and conditions are favorable for scab development consider applying Prosaro, Caramba, or Folicur for scab suppression and control of the other diseases just mentioned. For a table that rates the efficacy of fungicides for use on wheat diseases see the following link to the Kansas State fact sheet with the NCERA-184 ratings. This is a group of wheat pathologists from across the country that collaborates on wheat disease control. http://www.ksre.ksu.edu/library/plant2/ep130.pdf

Head Scab Risk Assessment Tool
Scab is still the one wheat disease that can cause major economic losses if weather conditions are favorable prior to and during flowering. The tools that we have to manage scab are limited but the use of rotation, resistant varieties and fungicides can help reduce the losses from scab should it appear. One of the tools that we have to help predict its occurrence and aid in making fungicide application decisions is the Head Scab Risk Assessment Tool that is found on the wheat scab website http://www.wheatscab.psu.edu/. The site provides information on how to use the tool and its limits.

 

Small Grain Disease Update – April 29, 2011

Friday, April 29th, 2011

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

Wheat is developing rapidly with the recent increase in temperature. Be sure to keep scouting for the presence of diseases, especially powdery mildew, at this time. It is important to keep the uppermost two leaves as free of diseases as possible to protect yields. At the most, you can wait until you see 5- 10% of the upper two leaves infected before applying a fungicide. Tilt, Stratego, Twinline, and Quilt can be applied as late as heads emerged but not yet flowering.

If scab should be a concern this year it may be best to use only a triazole fungicide at heading through flowering to avoid mycotoxin issues if scab infection occurs. There is evidence that if fungicides containing strobilurins (Quilt, Twinline, Stratego) or strobilurins alone are applied during heading up to flowering, they can increase mycotoxin production if scab occurs during flowering. If a fungicide is needed as late as flowering for powdery mildew, Septoria leaf blotch, tan spot, or other disease and conditions are favorable for scab development consider applying Prosaro, Caramba, or Folicur for scab suppression and control of the other diseases just mentioned. For a table that rates the efficacy of fungicides for use on wheat diseases see the following link to the Kansas State fact sheet with the NCERA-184 ratings. This is a group of wheat pathologists from across the country that collaborates on wheat disease control. http://www.ksre.ksu.edu/library/plant2/ep130.pdf

Head Scab Risk Assessment Tool
Scab is still the one wheat disease that can cause major economic losses if weather conditions are favorable prior to and during flowering. The tools that we have to manage scab are limited, but the use of rotation, resistant varieties and fungicides can help reduce the losses from scab should it appear. One of the tools that we have to help predict its occurrence and aid in making fungicide application decisions is the Head Scab Risk Assessment Tool that is found on the wheat scab website http://www.wheatscab.psu.edu/. The site provides information on how to use the tool and its limits.

 

The Dexisions You Make Pre-Season Have the Greatest Affect on Wheat Scab and its By-Product Vomitoxin

Friday, August 20th, 2010

Arvydas (Arv) Grybauskas, Extension Plant Pathologist, University of Maryland; arvydas@umd.edu 

Fusarium head blight (FHB) or head scab is a serious disease of small grains that does not develop every season. As a consequence we tend to drop our guard or just operate as we always have done because it is not front and center in our minds. The last big one was now two seasons ago, and only a few growers experienced vomitoxin (DON) levels above 1 ppm last season. Vomitoxin is the toxin produced by the fungus that could result in rejection of loads at the elevator or mill. Diseases are always the result of a combination of factors. We have a general rotational sequence of field crops that puts us at risk of scab every season. A serious outbreak of scab is highly dependent on weather conditions just prior to flowering through grain development. Weather is obviously something we cannot control but that does not mean there aren’t things we can do to reduce the risk of scab and ensure a harvestable crop.

We have been conducting scab management research with funding from The Maryland Grain Producers Utilization Board, the US Wheat and Barley Scab Initiative and the University of Maryland Experiment Station, which illustrates the importance of integrating management practices. The data that follows demonstrates that:

1) No one tactic (ie. fungicide or resistant variety) is sufficient in a serious outbreak;

2) Fungicides, although vastly improved and still an important tactic, provide the smallest increment in reducing DON;

3) Distance to a source of inoculum (primarily infested corn stubble) has the largest effect on scab, followed by resistant varieties and fungicides.

4) Management of scab is best achieved by integrating practices that minimize in-field inoculum and take distance to a local source into consideration, selecting varieties with some resistance, and using fungicides when needed.

The management research was conducted using 6 wheat varieties representing the range of resistance to scab that was known and was commercially available. To keep things brief we will focus on DON levels to illustrate the effects of resistance and other management practices. Varieties were ranked on the basis of DON levels based on trials conducted over several season in inoculated nurseries and naturally infected State wheat trials. A percentile was then calculated so that a variety with a 0.9 percentile means it is in the 90th percentile or is in the top 10% of resistant varieties tested. A variety that had a percentile of 0.1 means it had high levels of DON on average and is in the bottom 10% of tested varieties. Wheat trials were planted with all six varieties at the Wye and Beltsville facilities of the University of Maryland Experiment Station. All sites were turbo-tilled and each location had a planting where the previous crop was corn and another planting where the previous crop was soybean. A major difference between locations is that wheat planted into soybean stubble at the Wye was surrounded by corn, whereas at Beltsville the nearest corn stubble was about 300 ft to the south for the soybean-wheat rotation. This difference greatly affected scab development and DON levels. At the Wye wheat following soybeans had DON levels only 10% lower than wheat following corn, whereas at Beltsville DON levels were 40% lower in wheat following soybeans (Table 1). This illustrates that the most important source of spores for scab development is within the field, and that nearby sources provide background levels of spores that can still infect a crop regardless of rotation. Nevertheless, by reducing the spore load with a rotation away from corn (or wheat) even in a very disease favorable year and a highly susceptible variety, DON levels are close to 1 ppm and could be mixed with clean seed to be marketed.

Variety selection is clearly a very important tool to reduce the potential for DON levels that could make or break your season. Even varieties in the middle percentiles have a huge advantage over highly susceptible ones. Yet no variety by itself under high disease potential consistently had DON levels below 1 ppm. Fungicides provided another increment of DON reduction averaging about 40%. Yet 40% of 2 ppm is still above the stringent FDA guideline of 1ppm for human consumption. Combining resistance to DON from a variety that is in the 75th percentile or above with the recommended fungicides can get us very close to 1 ppm or at least to levels that could be mixed with clean seed to market. Combining all three tactics, rotation with resistance and fungicides when needed is the best way to keep scab and DON from destroying your crop. Rotation and variety selection is a pre-season management decision. The time is now to make the best management choices, a table on varietal rankings based on DON levels is provided to help make the choices.

Table 1. Scab Management Research 2009 – Effect of rotation, cultivar and Prosaro fungicide on DON (ppm) in wheat. Dr. A. Grybauskas and E. Reed, Univ of Maryland.


Highest risk of scab following no-till corn. Wye 2009 soybean site within 100 ft of corn stubble, therefore risk was practically unchanged. Whereas at Beltsville, source of spores (corn stubble) further from soybean site and disease reduced dramatically.

Summary of Vomitoxin (DON) Levels Due to Scab Infection and Percentile Rankings of Cultivars in Wheat Trials in Maryland

 

1The proportion of cultivars that have higher levels of DON under the same conditions, eg. 0.9 = 90th percentile where 90% of the population had higher levels of DON, or entry was in the top 10% of the population. Percentiles calculated over all available trials.

Red Text top 30% based on DON assessed over all trials.

Data from Dr. Jose Costa, U of MD; includes inoculated and misted scab nurseries 2008 & 2009, and naturally infected State Wheat trials at Queenstown and Keedysville in 2009.

Summary prepared by Dr. Arv Grybauskas, U of MD (revised 5/19/2010).

Note: Resistance to the visual blighting, bleaching of spikelets and poor grain fill is not completely correlated to resistance to DON development. Thus some low DON cultivars still suffer yield loss due to scab. For example, Pioneer 26R15 has greater resistance to symptom development than Chesapeake but Chesapeake tends to have lower DON levels.