Managing Fusarium Head Blight in Small Grains: Symptoms, Favorable Environments, and Disease Management Strategies
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.
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
This article appears in May 2023, Volume 14, Issue 2 of the Agronomy News.