New Eyespot Ratings Provide Useful Guide to Growing Disease Risks
Farmers concerned about the growing threat of eyespot in maize have new data on varietal tolerance they can use to help reduce disease risks.
The information, produced for the British Society of Plant Breeders (BSPB) by NIAB, is featured for the first time on the UK Descriptive List and shows some big differences between major maize varieties.
Ratings – on a 1-9 scale – have been based on two years of trials sited near Cambridge, which were inoculated to provide a consistent level of the disease across all plots.
All 90 or so varieties on the Descriptive List, including those in their second year of National List trials were tested with some varieties rated as low as 2.2 the most tolerant as high as 7.7.
Stand out variety for tolerance to the disease is Salgado, a first choice early maize for less favourable sites, which is 1.2 points ahead of all others.
Eyespot is firmly established in the SW and crops are affected every year, but according to Agrii national maize crop manager, Brendan Paul, who is also BSPB maize panel chairman, it is spreading to other regions.
“We are increasingly seeing it in S Wales, Worcestershire, Shropshire even in parts of Cheshire as well as throughout the SE of England,” he says. It spreads as a result of early rain-splash from inoculum left over from previous crop residues up on to the plant and also by wind later on in the season.
Mild, wet years are eyespot years and the disease is very quick to move through the crop. It can infect the crop in early June at the six to eight leaf stage, but causes more damage when it comes in late to take out the top leaves, which contribute most to yield.
Later infections in cool, wet conditions in September can cause significant plant rotting and at this late stage, you can go from a good looking plant to 70-80% fresh weight losses in 7-10 days.
While there’s a range of fungicides to control the disease, Mr Paul says that it is difficult to treat and even high clearance sprayers going through the crop at the 10-12 leaf stage cause damage. “It is also being exacerbated by more multiple cropping of maize and with bad infection crops can be written off.”
While 2014 hasn’t favoured the disease, low levels have been held over in soils on infected stubbles and later infections are possible.
Currently, all NIAB trials are sprayed as an insurance measure, so these cannot provide a measure of eyespot tolerance. While natural levels of the disease are high in the SW, siting trials where there is too much natural inoculum would make it impossible to get an even infection across all plots.
“This is why we site the trial in Cambridgeshire where eyespot pressures are low: All plots were evenly inoculated so that fair comparisons between varieties could be taken,” says Mr Paul.
He points out that Salgado has looked to have good tolerance to eyespot for some time. “We’ve noticed its higher tolerance for 6-7 years and now, we have the data to back this up.
“On the back of its better tolerance, we are tending to use Salgado in mixes in fields in regions such as the SW with newer, earlier material such as Fieldstar.
“This has been highly beneficial, helping to cut the eyespot risks and yet still gain a good yield from two different types in the same field, with Salgado proving consistent for silage, grain, crimping and biogas,” says Brendan.
KWS UK’s maize product manager, John Burgess points out that Salgado has been on the Descriptive List for eight years – since 2007. “No variety has been on the list for longer and it is its resilience and stay-green nature under significant eyespot pressure that have almost certainly helped keep it in the market,” he says.
“Over this period, breeders, including ourselves, have focused on earlier maturing, higher yielding types. These varieties also flower earlier and, with pollen a host for the disease, are commonly more at risk of eyespot.
“The problem is that you can’t breed for eyespot tolerance – we don’t have the genetic markers. However, we can select for it and our trials in the eyespot hotspot of the SW help us to discard material that is weak against the disease,” says Mr Burgess.
Brendan Paul says that some breeding programmes select types that may be more susceptible to eyespot attack. “Going forward it is important that all breeders look to a more diverse range of material and introduce varieties with better eyespot tolerance scores, generating their own data to support these new types.”
His advice to farmers is to use the new eyespot scores as a guide in at risk regions, but not to ignore the fungicides that are available. “We need both to ensure yields aren’t compromised.”