Winter wheat is starting to flower throughout Manitoba and that means the spray window for preventing fusarium head blight is also upon us.
The quality- and yield-robbing fungal disease can be prevented with fungicide applications on both winter and spring wheat — but only if the timing is just right, according to Pam de Rocquigny, Manitoba Agriculture’s cereal crop specialist.
“You want to target early anthesis,” she said in an interview June 8. “Target when 75 per cent of the main stem heads are fully emerged to when 50 per cent of the heads on the main stem are in flower. Always refer to product labels to make sure you are applying it at the time and the rates that the manufacturer is indicating on its labels.”
Before spraying, farmers should assess how much risk fusarium presents. Plant diseases need three conditions to exist: the pathogen, a host crop at the right stage to be infected and the environmental conditions for the disease to develop.
The fusarium head blight is prevalent in Manitoba so if the weather is conducive, there is likely to be a lot of fusarium head blight spores around. Fusarium likes warm, moist conditions.
Manitoba Agriculture posts fusarium risk maps, but also cautions local conditions may vary. That’s why farmers need to scout their fields. They should be doing so anyway to track the development of leaf diseases such as tan spot, de Rocquigny said.
Many farmers tend to apply a fungicide too late, Souris-based Manitoba Agriculture crop production adviser Lionel Kaskiw said during the CropTalk Westman webinar June 8.
“A lot of producers seem to be waiting to see the anthers on the head,” he said. “That’s when the head is done flowering. At that point you are past the flowering stage so you are actually late for the application.”
Tan spot too
Another fungal disease, tan spot, is showing up in spring and winter wheat fields. One option to consider is adding a fungicide when spraying a herbicide, but farmers should assess the risk the disease poses and the economics of early control, de Rocquigny said. Spraying at the five- to six-leaf stage will protect those leaves from tan spot, but it won’t protect leaves that form after the fungicide is applied.
“You still may need to do another fungicide application,” de Rocquigny said.
In winter wheat, if the disease is still in the lower canopy and the crop is close to the flag-leaf or flowering stage, a farmer might want to delay spraying. Applications aimed at protecting the flag leaf from disease or the head from fusarium will also control tan spot, she said.
“Studies conducted by NDSU (North Dakota State University) over the last 20 years have shown that a two- to six-bushel (an acre yield) response occurs when an early-season fungicide was used in a wheat-on-wheat production system with minimum tillage when favourable (disease) weather was present,” de Rocquigny wrote online in Crop Chatter.
“The incorporation of other management tools such as crop rotation and tillage will reduce the risk of tan spot development and reduce the expected yield response. Also, remember an early-season fungicide will protect the leaves available at the time of application, but as the wheat crop matures, newly developed leaves will be left vulnerable to leaf spot and rust pathogens.”