Prairie Crop Disease Monitoring Network: August 2022

Fusarium head blight and fusarium damaged kernels

Wheat and barley disease information cards

With maturity and harvest, one may assume that there are no further opportunities to obtain plant disease information from your 2022 crop. However, checking harvested grain for disease issues will allow you to assess potential impacts on grade and the presence of mycotoxins. In addition, if you are planning on using some of the harvested grain for seed then testing the grain can help to identify potential seed health issues for the 2023 growing season.

Sooty moulds

In challenging years when wet conditions delay harvest (e.g. 2016 and 2019), one issue that can be of concern is the development of sooty moulds. Sooty moulds (or molds) are due to saprophytic fungi including Alternaria and Cladosporium species. These fungi grow on dead plant tissues when sufficient moisture is present. Delayed harvest and wet conditions can result in your crop going from a nice golden brown colour to a dusty charcoal black or dark blackish olive green colour, which is due to fungal growth on mature dead tissues. If conditions are dry and harvesting is not delayed, sooty mould issues are typically limited. Typical symptoms of sooty mould are shown below.

Sooty mould symptoms on ripened wheat head tissues.

Sooty mould symptoms on ripened wheat tissues.

Sooty mould symptoms on ripened wheat head tissues.

Sooty moulds can also occur on prematurely senesced plant tissues. Premature ripening within a field can be due to abiotic (non-living) or biotic (living) factors. Abiotic factors include extreme heat stress, frost, flooding in low areas during the growing season, etc. In contrast, biotic factors that cause premature ripening include severe disease development especially due to root rots (e.g. take-all root rot of wheat, clubroot of canola, Aphanomyces of field peas). Insect damage due to wheat stem maggot, etc. can also be responsible for premature plant ripening.

Prematurely ripened wheat plants due to take-all root rot.

Take-all root rot symptoms in wheat showing charcoal black discolouration of lower stem bases.

Take-all root rot symptoms in wheat showing prematurely ripened tissues due to charcoal black discolouration of lower stem bases.

Take-all root rot symptoms in wheat showing significant root tissue destruction and charcoal black discolouration of the remaining root tissues and lower stem bases.

Sooty mould development on prematurely ripened wheat heads due to take-all root rot.

Sooty mould development doesn't necessarily result when you have complete plant death. These pictures show sooty mould development (blackish growth) on wheat head tissues killed due to fusarium head blight. Note the orange/pinkish growth (sporulation due to the rain-splashed spore stage) of the fusarium pathogen.

Early stages of sooty mould development (blackish to dark olive green fungal growth) on prematurely ripened wheat head tissue. Note the absence of fusarium head blight symptoms.

Sooty mould development (blackish to dark olive green fungal growth) on prematurely ripened wheat spikelet tissues due to fusarium head blight. Note the presence of orange-pinkish sporulation due to the asexual rain-splashed spore stage of one or more Fusarium pathogens.

Very early development of sooty mould development (blackish to dark olive green fungal growth) on prematurely ripened wheat spikelet tissues due to fusarium head blight. Note the presence of orange-pinkish sporulation due to the asexual rain-splashed spore stage of one or more Fusarium pathogens.

Seed testing results

Over the fall of 2022 and winter of 2023 you may be looking at seed testing lab results as you prepare for the 2023 season. Of note may be presence of Alternaria spp. on the seed. Don't be too alarmed as it is normal to detect Alternaria spp. It doesn't necessarily cause seed germination issues, although it may be indicative of weathering due to a delayed harvest and potential development of sooty moulds. If you find levels of Alternaria spp. that range from 10-40%, but the germination level is good (e.g. >95%), the seed should be fine for planting in 2023. However, adding a good quality seed treatment with effective application technology can provide peace of mind and mitigate any potential issues affecting stand establishment. Make sure to talk with your seed health professionals on what they are finding in terms of fungal load, germination, and vigour.

Fusarium head blight and fusarium damaged kernels

One other issue that farmers may be seeing is downgrading in wheat and durum due to the presence of fusarium damaged kernels in areas where Fusarium graminearum is well-established and you have had increased moisture during head emergence and anthesis. This downgrading is most likely due to Fusarium graminearum and the presence of fusarium damaged kernels (FDK), while there may be underlying mycotoxin issues. Keep in mind that other Fusarium species may be present and more commonly found especially under drier conditions versus Fusarium graminearum.

Fusarium head blight symptoms in wheat. Note the presence of orange-pinkish sporulation at the base of the spikelet due to the asexual rain-splashed spore stage of one or more Fusarium pathogens.

Fusarium head blight symptoms in wheat. Note the presence of orange-pinkish sporulation in the crevices of the floret tissues of the spikelet due to the asexual rain-splashed spore stage of one or more Fusarium pathogens. Also present is the blackish-dark olive green growth of the sooty mould fungi on the prematurely ripened tissue.

Fusarium head blight symptoms in wheat. If conditions turn dry following infection there may not be much if any orange-pinkish sporulation in the crevices of the prematurely ripened floret tissues. However, one diagnostic feature of FHB is the browning of the rachis and peduncle tissue.

Healthy and typical chalky white shriveled kernel symptoms, i.e. fusarium damaged kernels.

Things become more challenging in areas where Fusarium graminearum is not present or present at low levels. Here the down grading you may be seeing in your wheat/durum can be due to other issues and not necessarily Fusarium graminearum. As a consequence mycotoxins such as deoxynivalenol aka DON may not be a concern. If you haven’t had issues with Fusarium graminearum on your farm in the past, the presence of FDK may be due to other Fusarium spp. (e.g. F. avenaceum) or in fact other non-Fusarium pathogens. The main non-Fusarium pathogen that can produce FDK-like symptoms is the leaf/glume blotch pathogen, Parastagnospora nodurum aka Septoria nodorum. The glume blotch pathogen produces brownish lesions on the glumes, but can also affect the seed. The leaf and glume blotch pathogen, Parastagonospora nodorum, aka Stagonospora nodorum/Septoria nodorum can produce FDK symptoms that mimic those caused by Fusarium graminearum. Figure 4-3 below is courtesy of the Canadian Grain Commission.

Symptoms of glume blotch pathogen infection of wheat. Photo courtesy of Randy Clear (retired), Canadian Grain Commission.

You can note symptoms of glume blotch in your fields prior to harvest. Typical symptoms include brownish or purple-brown lesions on glumes. Also if you look closely enough you may be able to see small brownish bumps or pycnidia covering the lesions. Pycnidia are asexual fruiting structures that produce the rain-splashed spore stage of the glume blotch pathogen.

Typical brownish-purply brown symptoms of glume blotch of wheat. Photo courtesy of Dr. Jeannie Gilbert (retired), Cereal Research Centre, AAFC Winnipeg.

Typical brownish-purply brown symptoms of glume blotch of wheat. Note the presence of the asexual fruiting bodies aka pycnidia that produce the rain-splashed spore stage of the glume blotch pathogen. Photo courtesy of Dr. Jeannie Gilbert (retired), Cereal Research Centre, AAFC Winnipeg.

Typical brownish-purply brown symptoms of glume blotch of wheat. Note the presence of the asexual fruiting bodies aka pycnidia (brownish bumps) that produce the rain-splashed spore stage of the glume blotch pathogen.

Typical tan-brown lesions of the leaf blotch phase of glume blotch of wheat. Note the presence of the asexual fruiting bodies aka pycnidia (brownish bumps) that dot the lesions. These pycnidia produce the rain-splashed spore stage of the glume blotch pathogen.

The Canadian Grain Commission has a great resource to illustrate typical FDK symptoms and those caused by other fungi. See: https://grainscanada.gc.ca/en/grain-quality/grain-grading/grading-factors/identifying-fusarium.html.

These pictures illustrate typical grain symptoms due to Fusarium graminearum, i.e. the chalky white shriveled kernels versus intact healthy kernels.

Typical grain symptoms due to Fusarium graminearum, i.e. the chalky white shriveled kernels versus intact healthy kernels.

Typical grain symptoms due to Fusarium graminearum, i.e. the chalky white shriveled kernels versus intact healthy kernels. Note Fig. 4.18 is courtesy of Randy Clear (retired), Canadian Grain Commission.

Typical grain symptoms due to Fusarium graminearum, i.e. the chalky white shriveled kernels versus intact healthy kernels.

This picture is of durum with kernels exhibiting symptoms of FDKs due to Fusarium graminearum. However, there are also other kernels with a reddish tinge. These reddish/pinkish symptoms are typical of the tan spot pathogen that can affect leaves, heads and grain, and are called red smudge, which is a grading factor especially in durum wheat.

Healthy, fusarium damaged kernels (chalky white and shriveled) and reddish discoloured (red smudge due to the tans spot pathogen) durum wheat kernels. The reddish/pinkish symptoms are typical of the tan spot pathogen that can affect leaves, heads and grain, and are called red smudge, which is a grading factor especially in durum wheat.

Healthy (middle) and and reddish discoloured (red smudge due to the tans spot pathogen) durum wheat kernels. The reddish/pinkish symptoms are typical of the tan spot pathogen that can affect leaves, heads and grain, and are called red smudge, which is a grading factor especially in durum wheat.

Typical tan-coloured lesions of the tan spot fungus of wheat and durum.

If you are in an area with no to a limited history of Fusarium graminearum, you may still have issues with downgrading due to FDK. In this case make sure to send your grain to a seed testing laboratory to have a fungal screen done and also test for the mycotoxin deoxynivalenol (DON). You may find that the FDKs in your wheat are actually not due to Fusarium graminearum, but other Fusarium spp. where DON is not an issue OR where they are due to other fungal pathogens such as the glume blotch fungus. Fungal screening and DON tests may indicate no Fusarium graminearum or DON, and thus you may be able to have your grade reassessed or at least open up additional market/end-use options, including using the grain for hog feed.

Wheat and barley disease information cards

The PCDMN has developed disease info cards for fusarium head blight of wheat and barley caused Fusarium graminearum. If you observed symptoms of FHB in your wheat and barley in late July and early August make sure to closely check the harvested grain for FHB symptoms. Again having suspect grain tested by a seed testing lab can provide information that may help with grading and mycotoxin issues, while providing additional marketing options. The PCDMN has also prepared a disease info card that outlines typical fusarium damaged kernel (FDK) symptoms as well as symptoms due to other issues that may be confused with fusarium head blight damage in harvested grain.

See:

PCDMN Disease info cards for wheat:

· Speckled leaf blotch

· Parastagonospora/Septoria leaf and glume blotch

· Tan spot

· Fusarium head blight

· Fusarium head blight seed infections

· Bacterial leaf streak

· Cereal rusts

Bacterial leaf streak

One additional concern in cereals in relation to seed and crop health is bacterial leaf streak, which is becoming an increasing concern for Prairie cereal producers. The PCDMN has developed a disease info card on bacterial leaf streak as well as posting some additional information earlier this summer.

See:

https://twitter.com/pcdmn/status/1555320801670438913

https://twitter.com/pcdmn/status/1522349120119259137

https://twitter.com/pcdmn/status/1546478451015778304

https://drive.google.com/file/d/1Z9YmfHLaYQ8qqejofUpDafy7mq8qmfQp/view?usp=sharing