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.
Alyssa Koehler, Extension Field Crop Pathologist | akoehler@udel.edu University of Delaware
Wheat anthesis (flowering) is underway and will be continuing for the next 1-2 weeks across the region. Up until the rains this past weekend, we have been at low FHB risk. We are currently tracking as medium-high risk for very susceptible varieties and low-medium risk for varieties with some level of resistance (Figure 1). If you are planning for wheat fungicide application, scout frequently, looking for yellow anthers in the center of the wheat head (Figure 2) to signal that flowering has begun (Feekes 10.5.1). Depending on the weather, we can usually expect flowers to start showing up on wheat heads 3-5 days after full head emergence, with cool weather this can stretch this process out to 7-10 days. Anthers can remain attached after flowering, but become a pale white. For best mycotoxin (DON) control, it is better to be at flowering or a few days beyond than to spray too early when heads are not out yet (especially those secondary tillers). Fungicide products should be applied at the manufacturers recommended rate with nozzles angled 30-45° from horizontal (30 degrees is better than 45). Nozzles angled both forward and backward or twinjet nozzles that spray in two directions give better contact with the head and increase fungicide efficacy. For ground sprays, fungicides should be applied in at least 10-15 gallons of water per acre; aerial applications are recommended at 5 gallons per acre.
Figure 1. FHB Risk Model for very susceptible (top) and susceptible varieties (bottom) May 3, 2023 (wheatscab.psu.edu).Figure 2. Wheat at flowering (Feekes 10.5.1) with yellow anthers visible 3-4 days after heads emerge.
Once wheat has flowered, symptoms of FHB are usually visible in 18-24 days, but cool weather can slow symptom development. Heads with FHB will have bleached florets or bleached sections of the head and may have pink growth on spikelets. Glume blotch may also be present, but typically has more of a grey appearance. You can follow these steps to assess the severity of FHB present in your field.
For every 10 acres of field, randomly select one spot to survey.
Keeping your line of sight above the wheat heads, walk 40-50 yards and randomly pick 10-20 heads to look at on the plant or detach and place into a bag. (Looking down may bias the heads you select).
Once you have randomly collected the heads, rate the percent of each head with symptoms of FHB (bleaching or pink growth on spikelets). You can use the scale below to help calibrate your eye (next page).
After you have recorded values for each head, determine the average percent FHB severity by dividing the sum of disease severities by the total number of heads collected. (Ex. You rate 10 heads with severity values: 0%, 10%, 30%, 0%, 0%, 20%, 10%, 0%, 0%, 0%. These add up to 70. 70/10 heads = 7% overall FHB severity). Higher levels of FHB are typically associated with elevated levels of DON and possible issues with yield and test weight. It is possible to have delayed or lower levels of symptoms and still have DON.
Repeat this assessment as needed to get an overall rating for the field. Fields with greater than 10% FHB severity are at higher risk for yield losses or elevated DON. Fields with elevated DON should be harvested as early as possible and you may want to consider increasing combine fan speeds and shutter openings to reduce the amount of scabby kernels harvested.
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 varieties as of May 19, 2020. Image from: wheatscab.psu.edu.
Wheat in the Eastern shore and the Southern part of Western shore of Maryland has finished flowering, except for a few late planted fields. Up in the North-western counties of the state (Frederick, Howard, Carroll, Harford) wheat is flowering currently. Past week’s low temperatures slowed the progress of wheat. Heads emerged but waited for a week or so to flower in several places. The FHB risk for Maryland does not show to be high currently. However, the unusual pattern of weather has caused several other foliar diseases to appear across the state. Fungal diseases such as Stagonospora nodorum blotch, Stagonospora tritici blotch, Tan spot, Powdery mildew and even some viral diseases such as Wheat streak mosaic virus and Soil-borne mosaic virus have been observed in wheat fields this year. It is important to remember that Strobulurin containing fungicides should not be applied at this stage. Fungicides will not be effective against any viral diseases. However, the FHB fungicides (Prosaro/ Caramba/ Miravis Ace) will be able to control the other fungal foliar diseases. 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. 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.
Nidhi Rawat, Small Grains Pathologist University of Maryland, College Park
Fusarium head blight risk to susceptible wheat varieties as of May 10, 2020.
Wheat in the Eastern Shore of Maryland and Southern Maryland on the west of shore is finishing up flowering. Wheat in the Northern parts is either flowering/ will soon start flowering. The FHB risk for this part of the state (Frederick, Carroll and Harford counties) is predicted to be moderate to high, especially if the wheat variety planted is susceptible. If the planted variety is resistant, the risk is not predicted to be particularly high. The recommended stage for application of fungicides on wheat is at flowering (50% of the main tillers showing yellow anthers) or within 4-5 days of that. The fungicides effective for FHB are 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.
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.
Dr. Nidhi Rawat, Small Grains Pathologist University of Maryland, College Park
Wheat in the Eastern Shore of Maryland has started booting and should be heading out soon. Barley is already flowering there. Note that barley does not show any yellow anthers at flowering and is prone to FHB as soon as it heads out of the boots. Wheat is considered to be at flowering when at least 50% of the heads of a field are beginning to show yellow anthers. With the recent rains FHB risk has increased to moderate/high level in the lower eastern shore counties. Growers here should keep an eye on the FHB risk in the coming days, as wheat heads and flowers here in coming weeks. Fungicides Prosaro, Caramba and Miravis-Ace should be effective in minimizing damage due to FHB in wheat, when applied at flowering. Strobilurin containing fungicides should not be applied now, as they might increase the chances of DON content in the grains. So far, no major concern from other diseases like powdery mildew or rusts has been seen in wheat in the state. Some low intensity incidences of tan spot were observed, which the FHB fungicides applied at flowering should be able to tackle. Up in the northern part of the state wheat is at second node to flag leaf stage, predictably around 2-3 weeks away from flowering.
Figure 1. Fusarium head blight risk to susceptible wheat varieties on April 26, 2020.
Let me know if you have any questions or concerns (nidhirwt@umd.edu).
Dr. Alyssa Koehler, Extension Field Crops Pathologist University of Delaware
With the mild winter, wheat and barley are moving right along. Planting behind corn is common in our region, but this maintains inoculum for Fusarium Head Blight (FHB). Fusarium species that cause FHB can infect both corn and small grains. Walking through fields with corn stubble, you may see orange growth on old debris (Figure 1). Wet spring conditions favor fungal sporulation that can lead to infected wheat heads. As the pathogen grows on debris, spores are released that can be rain dispersed or moved through air currents. As 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. Deoxynivalenol (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 still have elevated DON.
Figure 1 (left). Corn stubble with Fusarium sporulation that can contribute to FHB in wheat. Figure 2 (right). Wheat head showing bleached florets from Fusarium Head Blight.
As we approach heading and begin to think about 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. The Fusarium Risk Assessment Tool (www.wheatscab.psu.edu) is a forecasting model that uses current and predicted weather forecasts to predict FHB risk. The model is currently being configured for this season and should be accessible at the link above by the end of the first week of April. Historically about 70% accurate, this tool aids in assessing FHB risk as wheat approaches flowering and fungicide application decisions are made. The pathogen that causes FHB infects through the flower and rainfall 7 to 10 days prior to flower favors spore production and increases risk of infection. Optimal wheat fungicide application is at early flowering (10.5.1) to about 5 days after. Although new products like Miravis Ace can be applied earlier, it is still best to wait for main tillers to be at 10.5.1 or a few days beyond so that secondary tillers have a greater chance of being at 10.3-10.5.1. If you spray too early, heads that have not emerged will not be protected by the fungicide application. When wheat heads begin 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. Anthers can stay attached after flowering but usually become a pale white (Figure 3, next page). Triazole (FRAC group 3) fungicides that are effective on FHB include Caramba (metconazole), Proline (prothioconazole), and Prosaro (prothioconazole + tebuconazole). Miravis Ace (propiconazole + pydiflumetofen) offers a triazole + SDHI, FRAC group 7. 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. Flat fan nozzles pointed 90° down are great at covering foliage but they do not provide good coverage on heads, which is the target for FHB management. Nozzles that are angled forward 30-45° down from horizontal (30 degrees is better than 45) or dual nozzles angled both forward and backward give better contact with the head and increase fungicide efficacy. For ground sprays, fungicides should be applied in at least 10 gallons of water per acre.
Figure 3. From left to right: Feekes 10.3, Anthesis; Feekes 10.5.1 (yellow anthers beginning flowering); 4 days after anthesis (white anthers post flowering). Image: A. Koehler, Univ. of Delaware.
Thinking beyond this season, an integrated approach can improve management of FHB and help to keep DON levels low. In your field rotation plan, avoiding planting small grains into corn residue will help to reduce the amount of initial inoculum in your field. If you have soybean fields that can be harvested early enough for a timely wheat planting, this rotation helps to break up Fusarium inoculum. 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. Results from 2019 can be found at https://scabusa.org/pdfs/UMD_Misted-Nursery_Factsheet-2019.pdf. Remember that these trials are conducted under extreme disease pressure and you want to look at relative DON performance. Unfortunately, barley does not have any resistance to FHB. In UMD’s 2019 trial, Calypso had the lowest DON content in local barley varieties tested.
The 2019 UMD small grain variety trial data concerning Fusarium head blight (head scab) and DON vomitoxin information is now available. Click the link below to view the report:
