Andrew Kness, Agriculture Agent University of Maryland Extension, Harford County
As wheat approaches flowering, here is a final list of reminders/tips to make the most of your fungicide applications that are targeted to manage Fusarium head blight (head 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; Feekes 10.5.1) + about 5-6 days after. Late applications (4-6 days after anthesis) are better than early heading/head emergence (10.3) 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, 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.
Wheat at Feekes 10.5.1. Image: A. Kness, Univ. of Maryland
Nidhi Rawat, Small Grains Pathologist University of Maryland, College Park
Fusarium head blight risk to susceptible wheat varieties as of May 25, 2020. Image from: wheatscab.psu.edu.
Wheat is at the dough stage in the lower eastern and lower western shore of the state. Although, the map shows FHB risk to be high in this region, wheat is well past the stage of FHB infection and spray here. Several other fungal foliar diseases such as Septoria tritici blotch, Stagonospora nodorum blotch, glume blotch, and tan spot have been observed here because of the rains or overcast skies and low temperatures. In our experimental plots at Wye, we have even observed some specks of leaf rust and stripe rust diseases. However, the damage due to these diseases is not going to be substantial now, and growers in this region do not need to spray fungicides for controlling these diseases. In a normal year, now would be the time to start looking for bleached spikelets to assess FHB severity. However, due to the cold spring that we had this year, symptoms may develop late/may not be visible, and the DON content of the grains should be analyzed and considered as the sole basis of FHB losses. Up in the North, wheat has finished/is finishing up flowering. FHB risk for today appears to be low here, especially for a moderately resistant variety. Check the FHB risk map http://www.wheatscab.psu.edu/ to monitor the daily risk here. If you are worried about foliar diseases mentioned above, the triazole fungicides do an excellent job of controlling these diseases as well. Strobilurin containing fungicides should be avoided at this stage.
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).
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.
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:
Current risk for Fusarium Head Blight development on susceptible wheat varieties (eg Shirley) for May 3, 2019.
Wheat in the Eastern Shore of Maryland is beginning to flower or will do so
in a couple of days. With yesterday’s rains, and more showers coming our
way, the risk of Fusarium Head has increased significantly in this part of
the state. Growers with wheat flowering (50% of the main tillers showing
yellow anthers) are advised to spray head scab fungicides (Prosaro/ Caramba/
Miravis-Ace) at early flowering 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 2 weeks away from
flowering.
–Nidhi Rawat, Small grains Pathologist, University of Maryland
