Nidhi Rawat, Small Grains Pathologist University of Maryland
Welcome to the wheat and barley heading and flowering season, Maryland! This is the first FHB risk forecast for this season from me, and I will continue to provide you with regular commentaries over the next 6-7 weeks. Wheat is some weeks away from flowering, but barley is starting/ will soon start to head, especially in the Eastern shore of the state. Unfortunately, for barley, there are no FHB-resistant varieties available so far. So, if you have planted barley, keep monitoring closely for the FHB risk over the next couple of weeks. With the rainy spell of the last week, and some more rain forecasted this week, currently, the Epidemiological models are showing elevated FHB risk over the next 6 days. So, if your barley is starting heading you might consider applying fungicides on it. If you are still some weeks away from your barley heading, keep monitoring for the risk. Remember, the best stage for applying FHB fungicides on barley is when the heads are completely out of the boots. The FHB fungicides are triazole-containing products (Miravis-Ace, Prosaro, Prosaro-Pro, Sphaerex). Do not apply strobilurin-containing fungicides after heading. Wheat is not at a stage susceptible to FHB right now.
Some barley growers from across the state reported stunting, yellowing, and death of barley plants in their fields. The most probable cause of this issue in my opinion is freeze injury. Sudden dips in temperature after the plants caught up after winter may have led to the issue. I have discussed this issue with the other regional pathologists from the US, and they also report similar issues in North Carolina, Pennsylvania, and New York. They also think it to be a result of cold injury.
Seyedali Hosseinrad, Nidhi Rawat, Nicole Fiorellino, and Vijay K. Tiwari Department of Plant Science and Landscape Architecture, University of Maryland, College Park
Fusarium Head Blight of wheat and barley
Fusarium head blight (FHB) is a severe fungal disease that affects small grains, wheat and barley. It is particularly problematic in regions with wet and warm springs, such as the Mid-Atlantic region. FHB is caused by several species of Fusarium, F. graminearum being the most common in the USA.
Symptoms and signs: The disease primarily attacks the wheat and barley heads, or spikes, at flowering. Early symptoms of FHB include the appearance of small, water-soaked lesions on the glumes and awns of the heads. As the infection progresses, these lesions become larger, and the spikelets (sections of the heads) become brown and dry progressively (Figure 1a, b). In particularly conducive weather conditions, the spikelets may take on a pink or reddish color due to a mass production of fungal spores called sporodochia on the glumes. The disease causes the kernels to shrink or abort, leading to reduced yield, poor-quality grain, and in severe cases, crop failure (Fig. 1 c). In addition, the fungus also produces mycotoxins, such as Deoxynivalenol (DON), which is toxic for human and animal consumption. The epidemiology of FHB is complex and multifaceted and can be influenced by various factors, including weather conditions, crop management practices, and genetic susceptibility.
Figure 1. FHB symptoms on wheat and barley. A.) Wheat heads showing brown and bleached spikelets indicated by yellow arrows. B.) A malting barley spike showing bleached spikelets. C.) Fusarium damaged kernels.
Factors affecting FHB
Weather conditions play a major role in determining the severity of FHB in field conditions. The disease thrives in warm, wet environments and is severe in areas with high humidity and frequent rainfall. Wet weather conditions during the flowering stage of wheat development provide an ideal environment for the fungus to infect and proliferate on the developing grain heads. In particular, warm and humid weather between heading and anthesis (flowering) is highly conducive to FHB infection. Warm temperatures between 70 and 80°F are favorable for fungal growth and production of mycotoxins.
Crop management practices can also contribute to the development and spread of FHB in winter wheat. Practices such as reduced tillage and corn-wheat rotation can increase the risk of FHB infection. Reduced or no-tillage can leave plant debris on the soil surface, providing a potential source of inoculum for the fungus. At the same time, corn acts as a secondary host of the pathogen, allowing the fungal inoculum to build up in the soil over time.
Management of FHB
Effective management of FHB in winter wheat typically involves using an integrated disease management approach that incorporates a combination of cultural, chemical, and biological control measures.
Use of FHB-resistant varieties: One of the most important cultural practices for reducing FHB infections in wheat is the selection of resistant cultivars. Several wheat varieties have been developed with genetic resistance to FHB. In fact, the UMD small grain pathology program, in collaboration with the small grain breeding program, tests upward of 60 regional commercial varieties in their misted nursery in replicated trials every year to provide growers with a robust assessment of the levels of the genetic resistance of these varieties to FHB (https://psla.umd.edu/extension/md-crops). It is highly advisable for regional farmers to refer to these ratings for making their planting decisions to reduce the severity of infections in their crops.
Due to the importance of FHB in the Mid-Atlantic region, developing FHB-resistant varieties is one of the primary goals of the MD small grain breeding program, in addition to their yield and quality. Resistance to FHB is a complex genetic trait and is influenced by a range of genetic factors. So, any breeding program targeting to incorporate a high level of genetic resistance in their varieties has to pyramid several genes toward that goal. However, a high level of genetic resistance in barley is difficult to achieve on account of the lack of resistance genes available in it.
Chemical control: The use of fungicides is a key component of FHB management in wheat and barley. Fungicides can effectively reduce the severity of infections and minimize the production of mycotoxins. Fungicides with Group 3 and 7 FRAC code ingredients have been successful in controlling FHB. FRAC group 11 fungicides should not be applied for FHB, as there are reports of them increasing DON content in the grains. Several effective chemistries with a mix of active ingredients against FHB have recently been released by manufacturers, such as Prosaro-Pro and Prosaro by Bayer, Miravis-Ace by Syngenta, and Sphaerex by BASF. All these fungicides have been tested by the UMD Small grain pathology program and are found to be equally effective when sprayed at anthesis.
In addition to the chemistry of the fungicide, the timing of spraying is very critical in managing FHB. Spraying fungicides at anthesis (when yellow anthers pop out of the wheat heads) in wheat and heading in barley is important. As weather plays a major effect in determining the severity of FHB infection, the risk of FHB can be predicted with a significant correlation with conducive weather conditions. In conjunction with the US Wheat and Barley Scab Initiative, the MD small grain program releases FHB risk commentaries for growers registered with the FHB risk prediction website (https://www.wheatscab.psu.edu/). The growers are advised to register on this website to receive the alerts on their cell phones as text messages with advice on spraying decisions for FHB.
Biological control: Some biological control agents, such as bacterial and fungal species antagonistic to FHB, are available with the claims of reducing disease severity and mycotoxin production. However, the efficacy of these biological control agents is not high yet. Researchers at UMD are testing some new promising biological products currently under development, especially for the organic growers of the region.
Crop Rotation and Tillage: Other important cultural practices include crop rotation and tillage. Planting non-host crops such as soybeans in rotation with wheat can help reduce the amount of FHB inoculum in the soil, as corn is a secondary host of the pathogen and can increase inoculum build-up in the soil for the wheat crop. Reduced tillage practices that manage crop residue on the soil surface with minimal disturbance to the soil are helpful in reducing the amount of infected crop residue on the soil surface while minimizing soil erosion and loss.
Post-harvest management: Post-harvest management practices, such as grain cleaning and drying, can help to screen the Fusarium damaged kernels that are expected to have high levels of mycotoxin contamination in the harvested grain. Cleaning equipment such as air screen cleaners or gravity tables can remove lightweight and damaged kernels. Drying grain to a moisture content of 14% or lower as soon as possible after harvest can also help minimize mycotoxin contamination. The fungus may continue mycotoxin production at high moisture conditions in storage. Proper storage conditions, such as cool and dry storage facilities, can also help to prevent mycotoxin contamination during storage.
Fusarium head blight (FHB) is a significant fungal disease affecting wheat and barley crops in the Mid-Atlantic region, causing yield and quality losses. Small grain pathology and breeding programs are working on multipronged approaches to reduce FHB impact, such as using fungicides, developing resistant cultivars, and adopting cultural practices such as crop rotation and tillage management. Also, research and innovation are crucial to ensure the region’s long-term sustainability of wheat production.
For more information:
Gillum, M., & Van Sanford, D. (2023). Understanding the Effect of Fusarium Head Blight Resistance on Agronomic Characteristics of Soft Red Winter Wheat.
Singh, L., Wight, J.P., Crank, J., Thorne, L., Erwin, J.E., Dong, Y., Rawat, N. (2021). Evaluation of application timing of Miravis-Ace for control of Fusarium head blight and DON content in wheat. Plant Health Progress. 22: 94-100.
Singh, L., Wight, J.P., Crank, J., Thorne, L., Dong, Y., Rawat, N. (2020). Efficacy assessment of a new fungicide, Miravis Ace, for control of
Nidhi Rawat, Small Grains Pathologist University of Maryland, College Park
Fusarium head blight risk to susceptible wheat as of June 1, 2020. Visit www.wheatscab.psu.edu
Flowering is all finished across all counties of Maryland now, except for a few late planted fields in the northern part of MD that may still be flowering. Currently the risk of FHB is high in these areas and so FHB fungicides (Prosaro, Miravis Ace, Caramba) should be applied here. For most parts, wheat is now in the grain filling stage and should be ready for harvesting in the next couple of weeks. We experienced some showers this season, but the temperatures remained low, so symptom development in terms of bleached spikelets will be limited. It is advisable to get the DON content of the harvested grain analyzed before taking it to the market.
This is the last FHB risk commentary of the season, but feel free to contact me (email: nidhirwt@umd.edu) if you have any questions related to wheat diseases any time of the year!
Nidhi Rawat, Small Grains Pathologist University of Maryland, College Park
Fusarium head blight risk to susceptible wheat varieties as of May 7, 2020.
With the recent showers in the state, the risk of Fusarium Head Blight appears to be high. In the Eastern Shore and the Southern part of the state wheat is flowering/towards the end of flowering. Growers with their wheat still flowering or are within a window of 4-5 days of flowering are advised to spray head scab fungicides (Prosaro, Caramba, Miravis Ace). These fungicides do not need to be tank mixed with another product for spraying. The fungicide products should be applied at the full rate recommended by the manufacturers. Strobilurin containing fungicides should not be sprayed at this stage. Aerial application at a rate of 5 gallons per acre or ground application at 15 gallons per acre with 300-350 um droplet size is recommended. Spray nozzles should be angled at 30°-45° down from horizontal, toward the grain heads, using forward- and backward mounted nozzles or nozzles with a two directional spray, such as Twinjet nozzles. In the Northern counties, we are still around 7-10 days away from flowering.
Nidhi Rawat, Small grains Pathologist University of Maryland, College Park
Fusarium Head Blight Risk, May 3, 2020.
Wheat in the Eastern Shore of Maryland is flowering or will do so in a couple of days. With this week’s rains, and more showers coming our way, the risk of Fusarium Head has increased significantly in this part of the state. Growers are advised to spray head scab fungicides (Prosaro/ Caramba/ Miravis-Ace) at wheat flowering (50% of the main tillers showing yellow anthers) or within 4-5 days of this stage. These fungicides do not need to be tank-mixed with another product for spraying. The fungicide products should be applied at the full rate recommended by the manufacturers. Strobilurin containing fungicides should not be sprayed at this stage. Aerial application at a rate of 5 gallons per acre or ground application at 15 gallons per acre with 300-350 um droplet size is recommended. Spray nozzles should be angled at 30°-45° down from horizontal, toward the grain heads, using forward- and backward mounted nozzles or nozzles with a two-directional spray, such as Twinjet nozzles. Up in the North, wheat is booting and still roughly around 1-2 weeks away from flowering.
Andrew Kness, Agriculture Agent University of Maryland Extension, Harford County
Wheat is progressing rapidly across the state due to our mild winter. In the coming weeks, wheat will begin flowering and entering the most critical management stage for Head Scab or Fusaruim Head Blight (FHB). Scout fields as heads emerge and determine when they start to flower (yellow anthers emerging from the middle of the spike). At this stage you will need to make the call to apply a fungicide or not.
Figure 1. Left: Feekes 10.3. Middle: Feekes 10.5.1 (yellow anthers beginning flowering). Right: 4 days after anthesis (white anthers post flowering). Image: A. Koehler, Univ. of Delaware.
Right now, FHB risk is very low across the region, mostly due to the cool nights we are experiencing (Figure 2). However, conditions can turn favorable for FHB very quickly, so don’t fall asleep on it! FHB can sporulate and infect flowering spikes at temperatures in the 50s as long as adequate moisture and humidity is present.
Figure 2. Head scab risk to susceptible winter wheat varieties as of April 21, 2020.
If conditions turn wet, humid, and above 50 degrees at flowering, FHB risk will be high and you will have about a 5 day maximum window after Feekes 10.5.1 (start of flowering) to make a fungicide application to suppress DON vomitoxin. Optimal timing for a fungicide application is at Feekes 10.5.1 and up to 5 days after. University research has indicated that earlier applications at heading (Feekes 10.3-10.5) do not consistently reduce DON levels in the grain as compared to applications made at or shortly after flowering.
Even though it may seem a bit early and cool, continue to monitor the Scab Risk Tool (www.wheatscab.psu.edu/) to help you assess the risk of developing FHB in your wheat crop so that you’re not taken by surprise.
For fungicide recommendations and other application recommendations, click here.
72-hour risk for Fusarium Head Blight development on moderately resistant wheat varieties for May 10, 2019.
Wheat in the Eastern Shore of Maryland is finishing up flowering. The risk
for FHB is high. If you haven’t sprayed and you are still within 4-6 days
of flowering, you can still do so. Wheat in the Northern parts is heading
now and will soon start flowering. The FHB risk for this part of the state
is also predicted to be high, and the farmers should be prepared to spray
fungicides on their wheat when it flowers (50% of the main tillers showing
yellow anthers). The fungicides effective for FHB are Prosaro/ Caramba/
Miravis-Ace. The best stage recommended for spraying fungicides is early
flowering or within 4-5 days of that. These fungicides do not need to be
tank mixed with another product for spraying. The fungicide products should
be applied at the full rate recommended by the manufacturers. Strobilurin
containing fungicides should not be sprayed at this stage. Aerial
application at a rate of 5 gallons per acre or ground application at 15
gallons per acre with 300-350 um droplet size is recommended. Spray nozzles
should be angled at 30°-45° down from horizontal, toward the grain heads,
using forward- and backward mounted nozzles or nozzles with a two
directional spray, such as Twinjet nozzles. There has been no other major
disease being seen anywhere across the state in wheat so far.
–Nidhi Rawat, Small grains Pathologist, University of Maryland
Alyssa Koehler, Extension Plant Pathologist University of Delaware
Andrew Kness, Agriculture Agent University of Maryland Extension, Harford County
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.
Figure 1. Fusarium Head Blight Disease Cycle. For more information on the FHB disease cycle visit https://www.apsnet.org/edcenter/disandpath/fungalasco/pdlessons/Pages/Fusarium.aspx Image: apsnet.org.
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.
Figure 2. Wheat head with Fusarium head blight. Image: Andrew Kness, University of Maryland.
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.
Figure 3. From left to right Feekes 10.5, Feekes 10.5.1 (beginning flowering), Feekes 10.5.2 (flowering growth stage), Feekes 10.5.3 (full flower). Image: C. Knott, Univ. of Kentucky https://mccracken.ca.uky.edu/files/identifying_wheat_growth_stages_agr224.pdf.
24 hour Risk for Fusarium Head Blight development on susceptible wheat varieties (eg Shirley) for May 9, 2018.
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
