Variety selection key to reducing eyespot losses
Growers in high and medium rainfall zones across the Southern Region are being asked to keep a look out for eyespot in cereal crops this season after the disease made a surprise appearance in a number of wheat crops in 2015.
Historically, eyespot has been restricted in its occurrence but SARDI plant pathologist Dr Margaret Evans says it has become an issue for more growers in recent years despite the dry seasons.
The rise of the disease has been attributed to shorter rotations, stubble retention, early sowing and increased use of nitrogen, leading to denser crop canopies.
The disease thrives in periods of prolonged moisture or high humidity at the stem base early in the growing season.
“At the start of the season, rain splashes spores up from the stubble, infecting the base of the plant,” Dr Evans says.
“Then, as the name indicates, an eye-shaped lesion develops on the stem. The lesion is usually a dark, golden brown around the outside and has a bleached centre with black spotting in the middle. The stem is weakened by the lesion which means badly affected stems are likely to bend at this weak point.
Yield losses from eyespot are most obvious when caused by lodging, which is when plants infected by the fungus fall over in different directions and form a tangled mess on the ground, making harvesting difficult. The lesions themselves can also cause yield loss even where lodging does not occur, as they block the plant’s vascular system, restricting plant growth and grain filling.
“Eyespot is a bit unusual in that you don’t see symptoms in young plants and lesions are not visible until late in stem elongation or during heading, by which time it’s too late to manage the problem.”
Dr Evans says this makes it important to identify whether paddocks intended for cereals have eyespot prior to seeding. To check for eyespot, growers can either inspect stem bases of cereal crops at the end of grain fill or test for eyespot inoculum levels prior to seeding using PreDicta® B.
What makes controlling the disease more challenging for growers is the fact there are no registered fungicides for control of eyespot in Australia. However, the GRDC has funded research into the efficacy of fungicides for control of eyespot as well as research into genetic resistance to the disease in current wheat varieties.
Bread wheat varieties identified by this research as being least affected by eyespot include LongReach Trojan, Emu Rock, LongReach Spitfire and Sunguard as well as the long-season varieties Manning and LongReach Gazelle.
Varieties found to be most affected by eyespot included Axe, Mace, Shield, LongReach Cobra and Corack. The range of resistance to eyespot in current commercial varieties will allow growers to select less susceptible varieties and will provide breeders with opportunities to develop new varieties with better resistance to eyespot.
“As a result of the data generated by GRDC funded research we know that many common fungicides suppress eyespot and we anticipate that at least one fungicide will be registered in 2016 for use in managing eyespot,” Dr Evans says.
While most growers would be implementing a preventative spraying program for rust, Dr Evans says the timing of that is likely to be too late for eyespot.
“If fungicides aren’t applied while the canopy is open and before the stem starts to elongate then they’re not actually protecting the stem” she says. “They will still have some efficacy, but the later the crop is sprayed the less effective fungicides will be at reducing eyespot expression.”
Dr Margaret Evans
08 8303 9379
Follow this link to read the GRDC Eyespot in wheat fact sheet
GRDC Project Code DAS00139, AAG00002