Fusarium graminearum

FHB (scab, tombstone)
FHB is a fungus that infects cereal crops in Canada. There are many species of the fungus, but the most common and damaging one is Fusarium graminearum. Fusarium graminearum causes FHB and negatively affects the yield and quality of grain by affecting kernel development. In top grades, there is little FHB permitted. In the grading process, the term given to barley affected by FHB is fusarium mould.

The presence of FHB can lead to the production of mycotoxins. These are toxic secondary metabolites that are not destroyed during processing. The most common mycotoxin is Deoxynivalenol (DON), aka vomitoxin. The toxins are harmful for both animals and humans. Malting barley has a very low tolerance for the presence of DON. Feed grain limits of DON vary depending on livestock species, so have your infected grain tested for DON levels.
Conditions
FHB thrives in humid warm weather conditions. Development and release of spores require periods of rainfall and moderate temperatures of around 15-25 degrees celsius. Infection occurs during the flowering period, which can last up to 14 days.

How do I know if I have it?
FHB is most prevalent in Eastern Canada, Manitoba, Saskatchewan and the Midwest United States. However, it is moving westward into Alberta and areas of British Columbia. Most signs of infection present themselves by the end of July or early August. On top of normal crop monitoring the most effective time to scout for FHB is during the late milk to early dough stage. At this time the healthy tissues are still green, so noticing the infected discolored areas is easier.

In barley, recognizing FHB is not as easy as it is in wheat. The symptoms can very easily be confused with other diseases like kernel smudge or spot blotch and, in some cases, hail damage. Typical symptoms of FHB include:

  • visible as dark lesions of spots on the barley head
  • development of fungal mycelium and/or black-ish fruiting bodies on the hull, that release the wind-borne stage of FHB
Prevention practices
There are multiple measures you can take to protect barley, and other crops, from FHB. It is important to remember that there is not one magic bullet to prevent the spread of FHB, but rather the chances of successfully protecting the crop increase when prevention strategies are used together.
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Fusarium Head Blight
Fusarium is a large genus of filamentous fungi, part of a group often referred to as hyphomycetes, widely distributed in soil and associated with plants.
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If you are in an area where FHB is not found or present at very low levels, it is recommended to use healthy seed with no detectable levels of FHB to limit the risk of introducing it into your area. If you are in a region where the pathogen is well established, seed-borne disease is less of a concern in terms of introducing the pathogen. Instead, the issue becomes one of seed quality and whether the seed has good germination and vigour and will result in satisfactory stand establishment.

Testing seed for FHB is important to prevent its introduction into or spread through an area, so be sure to choose a lab with experience testing for FHB either via agar plate tests or DNA-based testing.

Adopt the practice of staggering your cereal planting to ensure different crops are flowering at different times. This will reduce the risk of all crops being exposed to the same disease at a vulnerable time.
All small grain cereals and corn are susceptible to infection. It is recommended to rotate to a non-host crop for at least two years. This will help to facilitate decomposition of infested cereal or corn residues and reduce the risk of FHB in following wheat and barley crops. Avoiding planting a cereal crop next to a field that was infected with significant FHB the previous year may also help to lower the risk.
Proper irrigation management can help control the moisture level of the crop to avoid conditions that favour FHB. The humid and warm environment created in its canopy can make a crop susceptible to the disease.

It is known that irrigated crops are infected at a higher rate than dryland crops. Also, the use of a sprinkler irrigation system is more likely to put the cereal crop at risk compared to a gravity irrigation system.

Despite the challenges, there are a few things that can be done to help mitigate the risk:

  • avoid over or under irrigation
  • be aware of when flowering begins and ends
  • be conscious of irrigation management to discourage drought stress during the tillering growth stage
  • avoid irrigating during the flowering period by filling up the root zone prior to flowering
  • ensure the canopy is kept dry during the flowering period to discourage ideal conditions for FHB infection
It is important to have a realistic expectation of what applying a fungicide will do. Fungicides will aid in the suppression of the disease, though their effectiveness is less well established for barley than for wheat. The use of fungicides is not guaranteed to protect your crop one hundred percent so only use a fungicide when needed.

Weather-based risk maps can help to identify areas where weather conditions are conducive to FHB. A fungicide is most effective when applied once heads have emerged from the boot, but may only provide suppression. A fungicide is useless if applied after symptoms have been observed.

Provincial governments and crop groups have developed or are working to develop FHB risk maps. These risk maps will highlight which areas are most at risk for a fusarium infection depending on the weather conditions and help determine efficient fungicide use.
If the disease is found before harvest, it is recommended to adjust the combine settings to blow the lighter infected seed out the back. Unfortunately, this strategy is more effective for wheat and less so for barley and oats. A cereal crop with a high level of FHB should be stored separately from a healthy crop at no more than 14% moisture to prevent the spread of mould.

Be mindful of protecting yourself from crop dust, especially from a field infected with FHB. Choosing a swather or combine with a closed cab, wearing overalls, goggles, and a mask will help protect individuals from the effects of crop dust.

Take caution when hauling, loading, and unloading grain infected with FHB to ensure it does not blow into neighbouring fields, roadways, or ditches.
Does FHB remain in the crop residue?
The FHB fungus overwinters in crop residue. Burning is not an effective course of action because it will not destroy the entire plant. Ensuring crop residues are cut into the smallest pieces possible and spread adequately will aid in their decomposition thus helping to lower the risk of FHB in subsequent crops, especially if a two year or more rotation between host crops is followed.

If proper management steps are not taken after an infection has been found, FHB will remain a threat. The infected left-over cereal or grass residue develops spores and will continue to spread in subsequent crops once the conditions are favorable and the crop is at a susceptible growth stage.