WithTheGrain: Eyespot risk down, but not out
Author: Quinton McCallum | Date: 17 Jul 2018
Early-sown cereal crops in the Southern growing region may still be affected by eyespot despite the overall disease risk being reduced this season.
Reduced eyespot inoculum levels following a late start and low rainfall during 2017, combined with a dry start to this season, means the 2018 disease risk has shrunk, according to South Australian Research and Development Institute (SARDI*) research scientist Dr Marg Evans.
“Given the way the start of this season has gone, eyespot risk is reduced,” she says.
“It’s a later start so the risk of yield loss is probably much less, but early-sown crops may still be affected.”
Paddocks with a history of cereal stubble retention, direct drilling, and those sown to susceptible varieties or successive cereals are at higher risk of being struck by the disease, according to Dr Evans.
“Eyespot is spread via rain splash so the spores develop on residues from last year and we presume it takes a little bit of rain for the spores to mature,” she says.
“Then in the next lot of rain, those spores will splash off onto a crop in that paddock and cause infection if there is a rainfall period of three consecutive days with three millimetres or more of rain.”
Dr Evans says pre-sowing PREDICTA® B soil samples are the best method to determine the risk of yield loss from eyespot, particularly after a break from cereals when it is impossible to predict likely inoculum levels.
Eyespot infection is likely to occur after a consistent period of rain and causes eye-like lesions on stem bases and lodging in cereals.
Monitoring for eyespot symptoms will not assist in decision making for that current crop.
“It (eyespot) can be very hard to see. It’s a very slow-growing disease so what tends to happen is that you don’t see it until after canopy closure and by then it’s too late to apply a fungicide,” Dr Evans says.
If eyespot is suspected in a crop, the best time to check for lesions is during grain fill, according to Dr Evans, with symptoms most prevalent in the bottom 10 centimetres of the stem.
“Sometimes one lesion can go the whole way around the stem if the variety is very susceptible and it’s been the right type of year,” she says.
“The lesions can be right down at the base of the plant as well, so you can strip back the leaf sheath on each of the stems and look for it.”
Lesions weaken the stem of cereals causing twisting, lodging and a layering pattern which makes harvesting difficult.
“Obviously lodging can occur for a range of different reasons but if you’ve got a wheat crop that’s lodging and you didn’t think it should then definitely have a look for eyespot,” Dr Evans says.
In relation to the treatment of eyespot, Dr Evans says to be wary of applying prophylactic fungicides this year because she is not convinced there will be a problem.
She says the decision to spray or not needs to be based on the known presence of significant inoculum levels, susceptibility of the variety sown, time of sowing and whether there were significant rainfall events during early to mid-tillering.
“Fungicide application for eyespot control also needs to be considered in the context of controlling leaf diseases and what effect that has on resistance build-up and on economics,” Dr Evans says.
“Growers should also be aware that some fungicides can only be applied once or twice during a single cropping season.
“This is particularly important if fungicide is applied early so that it can be done in the same pass as the herbicides and nutrients needed at tillering.”
If growers are applying fungicides the recommended time is during stem elongation prior to canopy closure and the suggested target is the plant base.
Applying a fungicide after canopy closure is not likely to be effective.
“Some people want to put it out at tillering, but the results can be less consistent than at the recommended timing, since infection can occur after the early fungicide effect has worn off,” Dr Evans says.
Recently, the registration of Aviator® Xpro® for eyespot in wheat has been approved, offering Australian growers a registered option where there previously were none.
In the Cereal Variety Disease Guide 2018, put together by SARDI Principal Cereal Pathologist Dr Hugh Wallwork, eyespot resistance ratings are included for the first time, though many varieties are yet to be tested and rated.
It is noted by Dr Wallwork that while there is little variation among varieties, those rated moderately susceptible (MS) or moderately susceptible to susceptible (MSS) would provide a useful level of resistance over varieties rated susceptible (S).
Despite having similar resistance ratings to their shorter counterparts, taller cereal varieties and those with weak straw strength will be more inclined to lodging.
Wheat varieties classified as susceptible include Axe, Beckom, Cobra, Corack, Cosmick, Cutlass, Grenade CL Plus, Harper and Hatchet CL Plus, while those listed as MS to MSS – and at a slightly lesser risk – include Forrest, Manning, Trojan, Darwin, Emu Rock, Pascal and Yitpi.
Barley varieties listed as MS include Compass, Rosalind, Scope and Spartacus CL, with Fathom, Oxford, Hindmarsh and LaTrobe classified as MRMS or MRMS-S.
The durum variety Aurora is classified as susceptible, with Hyperno and Saintly listed as MS. Saintly also has weak straw strength meaning it’s prone to lodging.
According to Dr Evans, the best long-term management strategy for eyespot is to keep inoculum levels below the level at which they cause yield losses.
With eyespot, this can require a significant break from cereals or burning infected cereal residues followed by a one-year break.
However, these options are often not desirable from economic, environmental or soil health standpoints, which means that eyespot management is generally reliant on fungicide and varietal strategies.
“Once there is a paddock with a problem, it will often need or take – and it depends on the levels – a two-year break from cereals to get the inoculum levels down again,” Dr Evans says.
“One year will reduce inoculum levels, but if the levels are high eyespot still may be at a high-risk or medium-risk of problems or yield losses after that one-year break.”
The GRDC is advancing growers’ understanding in the management of eyespot through its bilateral investment with SARDI.
As part of that investment, SARDI Regional Research Agronomist (RRA) Blake Gontar, based at Port Lincoln, is working in collaboration with plant pathologists to provide farming systems solutions and management strategies to a range of damaging diseases including eyespot.
The aim of the RRA program is to increase regional research capability and translation of priority national research outcomes relevant to industry regionally and locally, in collaboration with national grains research programs and agencies.
The GRDC has recognised that achieving practice change and translation of research outcomes and improved technologies is critical to maintaining industry competitiveness and growth.
The RRA programs will improve the uptake of research outputs, optimise the benefits of research and development to grain growers, increase the rate of adoption in cropping farming systems and develop capability for the grains industry.
*SARDI is a division of Primary Industries and Regions SA
GRDC Project Codes: DAS000139, CAS 00002, DAS00159.
Dr Marg Evans, 08 8429 2225, 0427 604 168, firstname.lastname@example.org
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