Scouting Fields for Fusarium Head Blight

Alyssa Koehler, Extension Field Crop Pathologist | akoehler@udel.edu
University of Delaware

Symptoms of Fusarium Head Blight.

Wheat anthesis will be occurring over the next few weeks. So far this season we have been at low FHB risk, but we will keep a close eye on the rain events predicted over the next two weeks. Some areas are getting a bit dry, so the rain is needed, but we hope for sun after rather than multiple grey days that keep canopy moisture high. If you are planning for wheat fungicide application, scout frequently looking for yellow anthers in the center of the wheat head to signal that flowering has begun (Feekes 10.5.1). Once around 50% of heads are flowering, fungicides (Caramba, Sphaerex, Miravis Ace, Prosaro, Prosaro-Pro) are most effective when applied within a 4-5 day window. Anthers can remain attached after flowering, but become a pale white (Figure 1). Once wheat has flowered, symptoms of FHB are 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 (Figure 2) 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 level of FHB present in your field.

Figure 1. 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.
  1. For every 10 acres of field, randomly select one spot to survey.
  2. 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. (You don’t want to be looking down and biasing the heads you select).
  3. Once you have randomly collected the heads, rate the percent of each head with symptoms of FHB (bleaching or pink growth on spikelets).
  4. 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% 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.
  5. 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.

Fusarium Head Blight Risk: June 1, 2020

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!

Fusarium Head Blight Risk: May 10, 2020

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.

FHB Risk: May 3, 2020

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.

Fusarium Head Blight Risk: April 26, 2020

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.

FHB map of Maryland showing low to moderate risk of head scab
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).

Managing Fusarium Head Blight

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.

 

Wheat Variety Selections—An Important Factor For Managing Head Blight

Andrew Kness, Agriculture Agent
University of Maryland Extension, Harford County

Compared to the 2018 wheat crop, 2019 was a much better year for Fusarium head blight (FHB, also known as head scab). Growing quality wheat in Maryland starts with proper variety selection. As you look ahead to the 2020 wheat crop, select wheat varieties that have good FHB ratings. There are no varieties with complete resistance to head scab; only varying degrees of susceptibility. Nevertheless, planting a somewhat resistant variety will go a long way in managing FHB and keeping vomitoxin levels (DON) lower in your grain compared to a susceptible variety.

To aid in your selection of wheat varieties, the University of Maryland screens several wheat varieties for their resistance to Fusarium graminearim, the causal agent of FHB. The results from the 2019 trials can be found here.

Additional considerations for FHB management include:

  • Planting behind soybeans rather than corn or other small grains. The FHB pathogen survives on residue of corn, wheat, barley, oats, and other grasses; however, it does not persist on soybean residue.
  • If planting into corn residue, consider tillage if it is an option for your farm. Sizing and burying corn residue will accelerate its decomposition and reduce the FHB pathogen survival.
  • Fungicides in spring 2020. Please note that fall fungicide applications do not have any effect on managing FHB. More information will be covered concerning fungicide recommendations in the spring, or read this article from earlier this year.

 

Checklist For Head Scab Fungicide Applications

Andrew Kness, Agriculture Agent
University of Maryland Extension, Harford County

wheat infected with head scab
Wheat infected with Fusarium head blight. Image: A. Kness, University of Maryland.

Wheat in the southern parts of Maryland will soon be flowering and the rest of the Maryland wheat crop will follow suit over the next few weeks. As wheat approaches flowering, here are a final list of reminders/tips to make the most of your fungicide applications that are targeted to manage Fusarium head blight (scab):

  • Use an effective fungicide. These include: metconazole (Caramba®), prothioconazole + tebuconazole (Prosaro®), prothioconazole (Proline®), and adepidyn (Miravis Ace®).
  • Apply an effective fungicide at the correct time. The most effective application window is from flowering (anthesis; Feeks 10.5.1) + 6 days after. Late applications (5-7 days after anthesis) are better than early heading/head emergence applications at reducing DON content in the grain.
  • Apply fungicides using the correct equipment. Ground applications should be made with 80-degree flat fan nozzles angled down from horizontal. For ground applications made at speeds over 6 mph, use a single nozzle angled forward (towards the grain heads), 30 degrees down from horizontal. For ground applications less than 6 mph, better coverage is achieved with dual forward and rearward facing nozzles, angled 30-45 degrees down from horizontal.
  • Sprayer should be operated to achieve droplet sizes of 300-350 microns.
  • Use 10-20 gallons of water per acre and keep the spray boom 8-10 inches above the crop.
  • For aerial applications: Use 4-5 gallons of water per acre. Fine to medium sized droplets (300-350 microns). Small aircraft should operate 8-10 feet above the crop; large aircraft 10-12 feet. Nozzles should be mounted to cover 65% of the aircraft’s wingspan and mounted as low as possible.

Managing Fusarium Head Blight

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.