Volume 38, Number 15 | OCTOBER 8, 2012
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PRACTICAL PRODUCTION TIPS FOR THE PRAIRIE FARMER
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Is it aster yellows? Aster yellows are taking the blame for low yields across the Prairies. Aster yellows is definitely a factor, but experts don’t agree as to how much damage it’s caused BY ANGELA LOVELL
I
t may be a little premature to blame all of the yield losses in canola and cereal crops this year on aster yellows. Although infection rates of aster yellows are considerably higher than average across the Prairies, there are also other factors that, in combination with aster yellows (AY), could have caused significant yield losses. Although AY has certainly been a major factor, environmental conditions and other diseases such as sclerotinia (in canola) and fusarium head blight or root rot have also taken a toll on yields. “There is a lot of sclerotinia in canola because we’ve had rains during the summer and heavy dews every night, and that is perfect conditions for sclerotinia to form,” says Brent Flaten, integrated pest management specialist with the Saskatchewan Ministry of Agriculture in Moose Jaw. “We also had hot temperatures while the canola was flowering, which probably blasted some of the flowers so they didn’t form pods, and the heat following a cool wet spring could also have caused yellowing off of leaves.”
WHAT IS ASTER YELLOWS? Aster yellows is a disease caused by phytoplasma, a wall-less bacteria that lives and reproduces in the phloem of the plant (the tissue that carries nutrients). Aster yellows is spread by sap-feeding insects, mostly leafhoppers. On the Prairies, AY is mainly spread by the aster leafhopper (Macrosteles quadrilineatus). The majority of the aster leafhopper population arrives in spring, on winds coming from the southern U.S. Before it can infect other
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plants, the leafhopper must first feed on infected plants for a substantial period of time to acquire the pathogen. After eight hours of feeding, there is still only a 50 per cent chance that a leafhopper
and says it was not uncommon to find 200 leafhoppers per plant. Evans suspects that damage from AY may also compound in the crop as it develops. The primary spread from incoming leafhoppers
Once visible symptoms appear, there is no effective chemical control and no tolerant crop varieties exist will become infected. Generally, only two to three per cent of leafhoppers are infected. But once infected, they remain infected for life. Once a leafhopper becomes infected, there is a delay before it can begin to re-infect other plants. This delay is roughly 10 to 18 days, depending on environmental conditions such as temperature. An infected leafhopper must feed on a healthy plant for a few hours to pass on the pathogen. It is possible for the aster leafhopper to overwinter in perennial weeds and grasses on the Prairies, but this doesn’t happen in large enough numbers to be of concern. The main sources of infection are the migrant populations, which generally arrive on the Prairies around the first week of June. Many arrive immediately ready to infect crops, so the disease spreads soon after their arrival. The leafhoppers are carried on air currents and get dropped over an area due to associated weather events. This year, they arrived early across the main crop growing areas of Western Canada, and in huge numbers. Ieuan Evans, a forensic pathologist with Agri-Trend Agrology Ltd., scouted many fields across the Prairies in early summer
leaves the plant more vulnerable to damage from the secondary spread, which hits when secondgeneration leafhoppers hatch later in the season. “You would expect that a primary infection rate of 10 per cent would correspond to a yield loss of 10 per cent,” says Evans. “But, with the secondary infection, I suspect that plants that were partially infected from the spread of the first generation of leafhoppers had seeds that had already sprouted or shrivelled in the pods. So in reality there may be potentially a 50 to 70 per cent yield loss in those infected plants. So those secondary infections, which look so innocuous, may in fact be causing even bigger losses by aborting the seed.”
HIGH INFECTION RATES The leafhoppers arrived unusually early this May, in massive numbers. “The high number of leafhoppers led to the high AY incidence we see this year in the three provinces in oilseeds and cereal crops,” says Dr. Chrystel Olivier, an entomologist with Agriculture and AgriFood Canada (AAFC) in Saskatoon, who tested samples of leafhop-
PHOTOS: CHRYSTEL OLIVER, AAFC
Symptoms of aster yellows on canola. pers from across Western Canada. “Also, over the past 20 years, it has been observed that the south winds have been coming earlier, therefore bringing the leafhoppers earlier in the season and increasing the chances of AY outbreaks.” Olivier suspects that more leafhoppers arrived already infected than usual — perhaps due to drought conditions where they originated in the U.S. Drought reduces the number of plant hosts available for leafhoppers to feed on, increasing the chances that they will be feeding on infected plants. As well, the mild 2011-12 Prairie winter might have increased the local population of overwintering infected leafhoppers.
YIELD LOSSES? At time of writing many provincial agronomists were still compiling yield data, so the full extent
In This Issue
of yield losses from AY or other sources is still uncertain. Estimates of the losses caused by aster yellows vary widely. Evans has seen some areas with AY infection rates as high as 40 per cent in canola, and thinks potential losses could easily be in the hundreds of millions of dollars “When you get a 30 per cent infection rate in a 50 bushel per acre canola crop you’ve now lost 15 bu./ac. of canola. At a cost of $15 per bushel, that’s $225 an acre loss,” says Evans. Olivier says that the only known information to date on yield losses caused by AY was a report from 1957 — a year when AY infection levels were similar to 2012. The 1957 report associated a 10 to 15 per cent yield loss in flax and barley with AY. “An analysis I did on canola in 2000 to 2004 showed that 30 to
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Wheat & Chaff ..................
2
Crop Advisor’s Casebook
6
Features ............................
7
Columns ........................... 23 Machinery & Shop ............ 30 Cattleman’s Corner .......... 37
Straight cutting the swath
ANNE LAZURKO PAGE 22
Machinery section “spectrackular”
SCOTT GARVEY PAGE 30
FarmLife ............................ 43