Pheromone traps give early OWBM warning

UK - May 28, 2009

National monitoring for orange wheat blossom midge (OWBM) activity signals the start of UAP agronomist Richard Beaumont’s own monitoring of approximately 5,000 acres of premium milling wheat in south east Kent.

Mr Beaumont is using 14 pheromone traps strategically placed in fields. The traps will be monitored daily with counts taken from about 9am.

Until five years ago, Mr Beaumont had only experienced sporadic damage from OWBM. Then bad damage to a valuable Xi19 milling wheat crop highlighted the need for an OWBM control strategy to protect yields.

“With crops grown for premium markets, there can be large financial repercussions on milling wheat if they suffer an OWBM attack, so monitoring is vital. I will err on the cautious side and start to spray if and when thresholds reach 80 – 100 in the pheromone traps to ensure the whole area is covered before higher thresholds are exceeded,” says Beaumont. “I will also be taking the flowering stages into consideration as there is a big difference between varieties and drilling dates. When thresholds are reached I will use chlorpyrifos as I know it works and is consistent. It is head and shoulders above pyrethroids when it comes to efficacy but we have to be aware of the environmental implications of this crop protection material.”

Dow AgroSciences technical expert David Roberts advises: “Pheromone traps provide the earliest warning of midge activity. It is best to place traps in fields that have experienced OWBM damage in the last two years, whatever the current crop, even if the field has been left fallow.

“The thresholds for pheromone traps are expressed on two levels: thirty or more midges caught per trap per day means a general risk to crops in the following week as fertilised females lay eggs; over 120 means a very high risk and wheat varieties at the susceptible growth stage that are not resistant should be sprayed immediately. If the number of midges caught is at the lower threshold, wheat ears should be assessed by fieldwalking in the evenings. Thresholds within the crop remain the same as last year: 1 midge per 3 ears of feed wheat, or 1 midge per 6 ears of milling/seed crops. If the upper threshold is met or exceeded in pheromone traps, there is no need to carry out an in-field inspection. The highest risk is on the three nights after numbers caught in pheromone traps increases.

"Where a risk assessment shows midge threatens a crop, the products Dursban WG and Govern, which contain chlorpyrifos, offer the widest window of application. Chlorpyrifos is the only product available that controls adults, eggs and hatching larvae. Pyrethroids will kill adult midges but not eggs laid the day before.”

To reduce adverse effects on beneficial insects, Dow AgroSciences recommend growers should consider leaving a 12 metre strip around field margins.