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.
48-hour risk for Fusarium Head Blight development on susceptible wheat varieties for May 20, 2019.48-hour risk for Fusarium Head Blight development on moderately-resistant wheat varieties for May 20, 2019.
Wheat in the North-western counties (Frederick, Howard, Carroll, Harford
counties) of the state is flowering currently. The FHB risk across the state
continues to be high, so if your wheat is flowering, it’s recommended to
spray fungicides for managing FHB. The best stage for spraying fungicides is
early flowering or within 4-5 days of that. The fungicides effective for FHB
are Prosaro/ Caramba/ Miravis-Ace. All of these fungicides are pre-mixed and
do not need to be tank mixed with any other product for spraying. Read the
label carefully for recommended rates and harvest restriction times.
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. Wheat in the Eastern shore is
already past the stage for both FHB infection and fungicide spray.
–Nidhi Rawat, Small grains Pathologist, University of Maryland
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
Andrew Kness, Agriculture Agent University of Maryland Extension, Harford County
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.
Wheat infected with Fusarium head blight. Image: A. Kness, University of Maryland.
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).
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.
Andrew Kness, Agriculture Extension Educator University of Maryland Extension, Harford County akness@umd.edu
Figure 1. Wheat head with Fusarium head blight. Image: Andrew Kness, University of Maryland
If you grew wheat this year, chances are you don’t have to look too hard to find head scab/Fusarium head blight (FHB). The excessive rainfall, humidity, and warm temperatures that we had around wheat flowering provided the perfect habitat for Fusarium graminearum, the causal agent of FHB, to thrive. If you have FHB, you have few options to manage it at this point in the season as you read in Bob’s article above; but what can you do in 2019 to better your odds (besides hope for little rain during flowering)?
To understand your options you need to understand the lifecycle and biology of F. graminearum. The pathogen survives on residue, particularly that of wheat, barley, and corn and will persist through the winter on this material. During periods of wet, humid, and warm temperatures in the spring, the fungus will produce spores. If wheat or barley is growing in the field, the spores are splashed up onto the heads via rain or irrigation, or carried by the wind. If the wheat or barley is flowering, the spore can germinate and infect the plant through the flower; it cannot get into the plant any other way. This is why we recommend fungicide application at flowering. Once the pathogen infects the wheat, it grows within the spikelet, bleaching it in the process (Figure 1) and infects the developing grain, causing shriveled, light weight, discolored kernels called tombstones. Infected grain may contain deoxynivalenol (DON) vomitoxin. FHB not only reduces yield, but has the potential to contaminate your grain with DON.
With that in mind, here are some tips for managing FHB in 2019:
Know your variety! If you plan to grow and market quality grain, then you need to know your varieties. Unlike barley, wheat does have some resistance to FHB, although it is not complete resistance. Some varities are more resistant than others, so my suggestion is to grow a variety that has the best resistance and yield potential. Consult with your seed rep and utilize the data from our wheat variety trials. A collaborative project between the University of Maryland and University of Delaware screens wheat varieties for resistance to FHB. The data can be found here, or call your Extension Office for a copy.
Use a fungicide at flowering. Unless we have an exceptionally dry spring, you’ll likely need a fungicide application to protect against FHB. Use the Scab Risk Assessment Tool to help assess your risk. Time your application at the start of flowering (Feekes 10.5.1) and up to 5 days thereafter. Triazole fungicides work best, particularly Caramba (metconazole), Proline (prothioconazole), and Prosaro (prothioconazole + tebuconazole). Do not use strobilurin fungicides! See my article in the April issue for more information on fungicide strategies.
New for the 2019 growing season will be a new product from Syngenta, called Miravis Ace (adepidyn). This will be a new mode of action fungicide (SDHI) to be used on FHB, and should help us with managing resistance by rotating it with the Triazoles. Preliminary University testing shows that Miravis Ace does well against FHB; however, claims of a wider application window seems questionable at this point, so application timing will still be critical.
Select your best fields. Since F. graminearum can survive on small grain and corn residue, planting wheat or barley behind soybeans is better than following corn. F. graminearum doesn’t survive well on soybean residue. If you are following corn, consider a light tillage pass with a vertical till tool to size residue. This will accelerate residue decomposition, killing some of the surviving F. graminearum.
It is important to utilize as many management strategies as possible for FHB. Host resistance can only provide about 50% FHB suppression in wheat (and 0% in barley), and fungicides can only provide 50% suppression at best. Growers must use a combination of variety selection, fungicides, and cultural practices to achieve a high quality wheat or barley crop.
Bob Kratochvil, Extension Agronomist University of Maryland, College Park rkratoch@umd.edu
Figure 1. Healthy (outside two heads) and Fusarium head blight diseased wheat heads. Image: APS.net
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.
Figure 2. Healthy and head scab damaged wheat kernels.
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.
24 hour Risk for Fusarium Head Blight development on susceptible wheat varieties (eg Shirley) for May 22, 2018.
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
24 hour Risk for Fusarium Head Blight development on susceptible wheat varieties (eg Shirley) for May 16, 2018.
72 hour Risk for Fusarium Head Blight development on susceptible wheat varieties (eg Shirley) for May 16, 2018.
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
