Wheat crops could be at greater risk from orange wheat blossom midge than last year, according to experts.
In many areas last season, wheat ears emerged early and crops were in flower before midge arrived, ADAS entomologist Steve Ellis explains. But this spring, crops are not as far forward and there is more chance of midge emergence coinciding with the susceptible ear emergence growth stage (53-59), he says.
“It’s very difficult to predict whether the two will tie-up and a lot depends on the conditions being right.” Soils need to be warm (>13C) and moist for larvae to pupate and emerge and still nights favour flight, he says. “If soil isn’t moist, larvae can return to the cocoon stage.”
Cocoons can survive in soil for 10-13 years, so even though midge incidence was low last year, susceptible varieties – ie any without OWBM resistance – could be at-risk if conditions are favourable, he says.
The emergence of orange wheat blossom midge larvae could coincide with susceptible wheat growth stages this year
Independent agronomist Sean Sparling expects wheat crops to be growing through the midge-susceptible stage from the last weekend of May to the middle of June. “Larval feeding induces premature sprouting, reduces Hagberg and exposes grain to secondary infection from fusarium.”
More varieties have OWBM resistance, but there are still no resistant milling wheats, which is a concern, he notes.
At-risk crops can be monitored with pheromone or yellow sticky traps and Dr Ellis suggests it is also worth placing traps in so-called “source fields” where midge has been a problem previously. “You can also get a lab to test a soil sample to determine background levels.”
But, traps or soil samples only indicate risk and are no substitute for looking for midge in fields, he says. Treatment thresholds are shown in the panel.
“Thresholds exist for good reason,” Mr Sparling says. “Previously, with chlorpyrifos as the only option for effective control, there has been concern about its impact on beneficials.”
- Midge thresholds
- Feed wheat – one or more per three ears
- Seed crops & milling wheat – one or more per six ears
- Adult midges are orange, about 3 mm long
- Adults rest at the crop base during the day and fly up to the ears in evening to lay eggs
See the HGCA website