Should I Worry About Late Season
Fusarium Infection in My Wheat?

Late season Fusarium head blight infection continues to be very perplexing (confusing) and is one of the questions most often asked when dealing with scab in wheat. For most plant diseases there is a strong correlation between observable injury and its impact on yield and/or quality. In the case of wheat this holds true in most incidences as well but when it comes to late season Fusarium head blight infection things may not appear to be what they are! For this reason, growers, consultants and ag-business should make pre-harvest assessments for Fusarium head blight a routine farm practice each year.

Although bleached heads (visual observations) is a good method of predicting potential tombstoned or "scabby" kernels, it does not take into account late infection by the fungus very well. In this case, the heads may not be bleached and have no apparent visible symptoms although the glumes and seed may be infected. Infected glume tips will often have a sunken lesion with a dark brown border very similar to Stagonospora glume blotch but without any pycnidia (black spots). During warm, humid weather the fungus produces a salmon orange to pink ring of spores at the base of the spikelet or in the crease of the kernel. If conditions continue the infection may spread to adjacent kernels. Infected kernels are usually shrunken, wrinkled and light weight. These kernels have a rough, scabby appearance and range in colour from light-brown to pink to grayish white.

The frequent rain showers and humid conditions over the past three or so weeks have been ideal for continued Fusarium or late season infection and growers are recommended to continue monitoring and assessing their entire fields in order to determine infection levels (risk) right up to harvest. I mention entire fields since infection levels can vary not only from field to field due to differences in variety susceptibility to the disease, planting dates, heading dates, etc but within the field as well.

One quick method is to examine 100 random heads throughout the field. Do this a number of times up to harvest since as I mentioned earlier, the frequent rain showers could have resulted in secondary Fusarium growth or a longer then normal infection period in your field. Conditions can change quickly and not doing so could result in grain quality issues at the elevator. If infection levels are 10% or higher it is advisable these fields be marked for harvest first and if possible keep separate from your other fields.

Storage and adjustments to the combine ground speed, fan speed and sieve settings have been used in the past by growers to reduce the number of infected kernels in their harvest sample and raise seed grade. This is particularly possible when your sample falls in the 2 to 3 % damage level.

Figure 1. Bleaching of wheat head due to fusarium infection.

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Figure 2. Bleached heads become obvious in field conditions.