Fusarium head blight (FHB) symptoms were appearing in unprotected winter wheat and spring cereal variety trials last week, but at low levels.
“Typically the symptoms start to appear anywhere from 14 to 21 days after infection,” Manitoba Agriculture cereals specialist Pam de Rocquigny said during the Westman CropTalk webinar July 27.
“For the most part it has been at low levels, which is good news, keeping in mind that the trials are not sprayed with a fungicide. We are measuring the genetic potential of the varieties in the MCVET (Manitoba Crop Variety Evaluation Trials) trials.
“Hopefully that translates into commercial fields where fungicides may have been applied and levels remain low as well. We are not typically seeing full heads impacted at this point. Usually it has just been part of a head or a spikelet or two. It has been at really low incidence levels to date.”
FHB is a fungal disease that can cut cereal yields and quality. If a field is infected farmers hope it occurs early so by harvest damaged kernels are lighter and can be blown out the back of the combine with the chaff by boosting fan speeds. Ontario research has shown this technique is effective, de Rocquigny said. While it means more potential for future infections, FHB is so ubiquitous in Manitoba it probably doesn’t matter, she said.
“The other option is to reduce your combine speed,” de Rocquigny said. “Hopefully that will allow for separation to happen… to separate the good kernels from those light weight infected kernels.”
FHB infected wheat heads often stand out because of their distinctive white colour. Upon closer inspection sometimes pink-to-orange-coloured mycelium can be seen on infected kernels. But not every white head is necessarily caused by FHB, de Rocquigny said. Wheat stem maggots can cause a similar appearance. Root rot can too.
“There have been lots of areas of the province where we have seen excessive moisture conditions that could potentially lead to increased root rot,” she said. “Infected plants will generally pull free from the soil without too much resistance.
“It could be other environmental stresses. Hot winds can result in these type of things as well.”
Typically winter wheat is the most susceptible to FHB, although because it flowers earlier than spring wheat, it sometimes avoids the disease which infects crops at flowering.
Canada Prairie Spring and Canada Western Red Spring are the next-most susceptible wheats. However, it varies between varieties. Emerson winter wheat and AAC Tenacious VB, a CPS wheat with midge tolerance, are both rated as resistant to FHB. However, de Rocquigny stressed an “R” rating for FHB doesn’t mean the variety is immune.
“You tend to see some symptoms in a high disease pressure year even when varieties have an “R” rating,” she said. “Breeders are making advancements for sure.”
FHB can also infect barley and oats. Low levels of FHB are visible in unprotected MCVET oat trials, de Rocquigny said.
For any plant disease to exist, the pathogen must be present, have a host and the right growing conditions. FHB inoculm is widespread in Manitoba and there are lots of cereals for it to attack.
“The environment is really the big card in terms of determining what levels of disease that we will see in any given year,” she said. “Mother nature kind of has the final say in many of the things that we do as farmers farming in Manitoba.”
FHB does well when temperatures are warm, but not scorching hot, with high relative humidity.