A new Section 3 MD label for Fusarium head blight (head scab) control on barley and wheat was just awarded for the Syngenta fungicide Miravis Ace, (see the label here: MIravis Ace Syngenta Label-ue1r8d).
See this article for more information on Fusarium head blight management, and stay on top of scab this year by subscribing to scabalerts and using the Fusarium Head Blight risk assessment map.
When it comes to controlling Fusarium Head Blight (FHB) and keeping deoxynivalenol (DON) levels low, it is important to have an integrated approach. Considering the disease cycle of FHB (Figure 1), the FHB pathogen (Fusarium graminearum and other Fusarium sp.) is able to grow on crop residues from corn and small grains. In your field rotation plan, try to avoid planting wheat or barley into corn residue; this will help to reduce the amount of initial inoculum in your field. As the pathogen grows on debris, it eventually releases spores that can be rain dispersed or moved through air currents. While the grain is flowering, spores land on the head or anthers, colonize these tissues, and move into the grain head. Once inside the grain, water and nutrient movement is disrupted which results in the bleached florets we associate with FHB (Figure 2). Shriveled and wilted “tombstone” kernels can reduce yield and result in grain contaminated with mycotoxins. DON, also referred to as vomitoxin, is a health hazard to humans and animals. Wheat heads colonized later in development may not show dramatic symptoms, but can have elevated DON.
In addition to rotation considerations, seed selection is another important piece of FHB management in wheat. There is no complete host resistance against FHB, but you can select wheat varieties with partial resistance. The University of Maryland sets up a misted nursery to compare FHB index and DON levels across local wheat varieties to aid in variety selection decisions https://scabusa.org/pdfs/UMD-UDE_Misted-Nursery_Factsheet-2018.pdf. Unfortunately, barley does not have any resistance to FHB. At this point in the season, rotation order and variety are established, but you can consider these factors as you plan for next season.
As we think about 2019 in-season disease management strategies, a well-timed fungicide application can help to reduce disease severity and DON levels. It is important to remember that fungicides can help to reduce disease levels and DON (traditionally around 50% reduction on a susceptible variety) but they do not eliminate FHB or DON. To try to maximize the efficacy of fungicides, it is important to apply at the correct timing. Fungicides for FHB are most effective when applied during flowering in wheat and at head emergence in barley. As wheat approaches heading, the Fusarium Risk Assessment Tool (www.wheatscab.psu.edu) is a forecasting model that uses current and predicted weather forecasts to predict FHB risk. This tool is historically about 70% accurate, and can help you assess your risk for developing FHB as your wheat approaches flowering. The pathogen that causes FHB infects through the flower, and rainfall 7 to 10 days prior to flowering increases spore production and risk of infection. Optimal wheat fungicide application is at early flowering (10.5.1) to about 5 days after. For initial signs of wheat heads beginning to flower, look for yellow anthers in the middle of the wheat head. When at least 50% of main stems are flowering, you will want to initiate fungicide applications. As the flowering period continues, anthers will emerge from the top and then the bottom of the wheat heads (Figure 3). Anthers can stay attached after flowering but usually become a pale white.
Method of fungicide application is also important. Flat fan nozzles pointed 90° down are great at covering foliage; however do not do a good job of covering the heads, which is where the product needs to be located. Use nozzles that are angled forward 30-45° down from horizontal (30 degrees is better than 45) or dual nozzles angled both forward and backward. Research has shown that a single forward-angled nozzle or nozzles angled forward and backward allow for significantly more product to contact the head and increase fungicide efficacy. Optimal spray volume is 10 gallons per acre.
Triazole (FRAC group 3) fungicides that are effective on FHB include Caramba (metconazole), Proline (prothioconazole), and Prosaro (prothioconazole + tebuconazole). This year, a new mixed mode of action product is on the market, Miravis Ace. This product contains propiconazole (DMI, FRAC 3) and pydiflumetofen (SDHI, Group 7). On the label, application can begin at Feekes 10.3 through 10.5.2. Although this product can be applied at the earlier timing, preliminary data has shown that optimal FHB control and lower DON levels are achieved at the 10.5.1 timing or a few days beyond this timing. If you spray too early, heads that have not emerged will not be protected by the fungicide application. Rainfall during flowering can increase levels of FHB and delay the ability to get into fields to apply fungicides. The expanded application window of Miravis Ace may offer options if periods of extended rainfall are in the forecast. However, if the weather allows, 10.5.1. to about 5 days after appears to provide the best control to reduced DON. We will be collecting local data on optimal application timing in Georgetown this spring. As a reminder, fungicides containing strobilurins (QoI’s, FRAC 11) should not be used past heading because these fungicides can result in elevated levels of DON.
Bob Kratochvil, Extension Agronomist
University of Maryland, College Park
rkratoch@umd.edu
During the past two weeks, I have had the opportunity to walk a number of small grain fields (wheat, barley, triticale) across the state. Many of those fields are infected with Fusarium head blight (FHB), aka head scab (Figure 1). I have seen fields with very low levels of infection (less than 1% of heads infected) to some that have over 50% infected heads. Thus, the reason for concern. The reason for the high number of infected fields this year is the rainy weather we have had during May. The rains coincided with flowering of the wheat, barley, and triticale. Rain splashes spores of the causal agent of the disease, F. graminearum, onto the heads allowing infection to occur. Temperatures ranging between 75 and 85°F are considered optimum but lower temperatures during periods of high humidity and moisture can also enhance infection. The over 10 inches of rain much of the state has received created ideal infection conditions.
Head scab often results in significant yield loss and grain quality reduction. Grain quality reduction is primarily the result of the mycotoxins (chemicals) that are produced by F. graminearum. These mycotoxins can be toxic for humans and animals if the concentrations exceed minimum limits. The most concerning mycotoxin is deoxynivalenol (DON), also known as vomitoxin. The Food and Drug Administration (FDA) advisory level for DON is 1 ppm for foods consumed by humans. In the case of wheat, the level is 1 ppm for the flour. Often elevators and mills will accept wheat with DON levels 1.5 – 2 ppm without penalty because they can blend infected grain with sound grain to meet the FDA advisory level. Wheat with DON levels that exceed 2 ppm can be acceptable livestock feed. Swine are the most sensitive with the recommended level of 5 ppm DON with the DON infected grain not to exceed 20% of the ration. For ruminants and poultry, grain with 10 ppm DON can be used as long as no more than 50% of the ration is composed of the infected grain.
When you harvest your grain and notice shriveled, whitish looking kernels (tombstones), there is a strong likelihood that DON is present (Figure 2). If you have head scab infected wheat or barley fields, you will want to do what you can to minimize the impact of DON that is concentrated in the shriveled tombstone kernels (Figure 2). These light-weight kernels can be separated from sound grain at harvest by increasing the combine’s fan speed so don’t be concerned that you are losing too much good grain if you see lots of tombstones behind the combine, because you are not.
If you are storing the grain do so properly to prevent further contamination. Dry newly harvested grain that is infected to 13-14 percent moisture. This will stop pathogen growth and mycotoxin production. DON is an extremely stable mycotoxin. This means that drying and properly storing grain will not reduce the DON levels, however, DON concentration will not increase in properly stored grain. Bin any infected grain you harvest separately from sound, good quality grain. If you have a cleaner, you can remove fines from the wheat before you bin it and possibly lower the DON concentration. Before you deliver your grain, I suggest you check with your elevator or mill to see if they test for DON. It will be easier to take samples to them for testing prior to delivery than to learn that your grain is rejected after you have loaded the truck and taken it to the elevator.
With the recent wet period and warm temperatures, FHB risk in the state of
Maryland continues to be very high. Growers having their wheat flowering now
are advised to spray triazole fungicides (Prosaro/Caramba) for FHB. Aerial
application at a rate of 5 gallons per acre or ground application at 15
gallons per acre with 300-350 um droplet size and nozzles angled down 30 to
45 degrees from horizontal is recommended. If flowering has finished,
fungicide spray will not help to reduce FHB and DON contamination of grains.
Do not spray strobilurin-containing fungicides.
–Nidhi Rawat, Small grains Pathologist, University of Maryland
For more details, go to the FHB Risk assessment tool at
http://www.wheatscab.psu.edu
For the latest news and updates from the U.S. Wheat & Barley Scab
Initiative, go to https://www.scabusa.org
Wheat is anywhere from beginning to heading to past-flowering in Maryland.
With the current wet weather, the risk of FHB is increasing in the region.
Farmers who currently have their wheat flowering are advised to spray for
FHB. Those who will have flowering in the coming week or so are advised to
be prepared to spray, keeping a close watch on the risk forecast. If the
wheat is already past flowering, you don’t need to spray. The fungicides
recommended for FHB are Prosaro, Caramba, or Proline. Do not apply a
strobilurin-containing fungicide.
–Nidhi Rawat, Small grains Pathologist, University of Maryland
For more details, go to the FHB Risk assessment tool at
http://www.wheatscab.psu.edu
For the latest news and updates from the U.S. Wheat & Barley Scab
Initiative, go to https://www.scabusa.org
For more information on fungicide recommendations, see this blog post: https://blog.umd.edu/agronomynews/2018/05/03/fusarium-head-blight-fungicide-recommendations/
Wheat growers in Maryland have so far been fortunate this year for having
low disease pressure from leaf rust, powdery mildew and even scab!! In the
south (Eastern shore), wheat is flowering currently. With consistently
warmer temperatures now, a few incidences of leaf diseases are being
observed. Triazole fungicides: Prosaro/ Caramba/ Proline that are the scab
fungicides should provide control against these as well. Strobilurin
containing fungicides should not be sprayed at this stage, as they may lead
to DON accumulation in grains. Up in the north, flag leaves are emerging. No
diseases being seen so far here as well. Growers should keep an eye on the
FHB risk, as crop heads and flowers here in coming weeks.
–Nidhi Rawat, Small grains Pathologist, University of Maryland
For more details, go to the FHB Risk assessment tool at
http://www.wheatscab.psu.edu
For the latest news and updates from the U.S. Wheat & Barley Scab
Initiative, go to https://www.scabusa.org
By Andrew Kness, Agriculture Extension Educator
University of Maryland Extension, Harford County
As wheat begins to head, growers will be considering fungicide applications for managing head scab/Fusarium head blight (FHB). The Fusarium Risk Assessment Tool (www.wheatscab.psu.edu) is a forecasting model that predicts your risk for developing FHB on your wheat based on the current and predicted weather forecasts. FHB infection is favored by wet weather and high humidity. You should use this tool to help assess your risk for developing FHB as your wheat approaches flowering. Historically, this tool has been about 70% accurate.
Management of FHB should start with seed selection, since fungicides can only achieve about 50% control under the best case scenario; so selecting resistant varieties is crucial for harvesting good quality grain. It should be noted that resistance to FHB in wheat is not complete; therefore, fungicide applications are often needed in order to achieve acceptable management of FHB and suppression of DON vomitoxin. The pathogen that causes FHB can only infect the plant through the flower, so fungicide applications should be targeted between early flowering (Feekes 10.5.1) and 5 days thereafter. Fungicides that are effective on FHB include the triazoles (FRAC group 3 fungicides), which are Caramba (metconazole), Proline (prothioconazole), and Prosaro (prothioconazole + tebuconazole). These fungicides will also do an excellent job on foliar diseases as well, helping to keep the flag leaf clean. Folicur (tebuconazole) is less effective, but provides some suppression of FHB and DON accumulation, but should not be used if FHB risk is high. Over the past few years, Tilt (propiconazole), has become less effective for managing FHB, and is currently providing poor control. Fungicides containing strobilurins (Qoi, FRAC group 11 fungicides and mix-mode of action fungicides) should not be used past flag leaf emergence on wheat because these fungicides can increase DON vomitoxin accumulation in the grain. For barley, fungicide applications should be made at head emergence. Unlike wheat, barley has no resistance to FHB, so if we get a highly favorable year for FHB development, the very best control you can hope to achieve of FHB and DON is about 50% suppression.
Wheat in southern Maryland is either at jointing or booting stage, and
should be heading out in a week or so. Even with the recent showers, the FHB
risk is currently predicted to be low because of the cold temperatures so
far. However, the temperatures are going to increase by next week, so
growers are advised to keep an eye on the FHB risk forecasts. Up in the
north in Frederick, Harford and nearby counties, plants are starting to
joint, and are not at a stage prone for FHB.
–Nidhi Rawat, Small grains Pathologist, University of Maryland
For more details, go to the FHB Risk assessment tool at
http://www.wheatscab.psu.edu
For the latest news and updates from the U.S. Wheat & Barley Scab
Initiative, go to https://www.scabusa.org
Nathan Kleczewski, Extension Field Crop Plant Pathologist, University of Delaware
We are through flowering in Delaware and Maryland wheat. Growers should assess wheat for FHB severity approximately 18-24 days after flowering or fungicide application. Check one transect per 1-2 acres of field. At each transect, pick 25 heads without looking at the field. Mark the number of heads with FHB out of the total heads collected (FHB incidence). Fields with high levels of FHB incidence should be harvested with increased fan speeds to remove tombstones and grain stored separately from that harvested from cleaner fields. If possible, harvest fields early and dry to at least 15% moisture to prevent continued growth of the FHB fungus and potential mycotoxin production.
Nathan Kleczewski, Field Crops Pathologist, University of Delaware
Heavy rains coupled with high winds made it difficult for growers in Delaware and Maryland to apply fungicides for Fusarium head blight (FHB) suppression. There has been discussion about waiting until this current weather front passes to make applications. READ THE REST ON NATHAN’S BLOG POST: