Trapping helps predict wireworm threat

Pheromone trapping can help potato growers estimate potential wireworm damage to future crops, say experts.

Over 95% of users of Syngenta’s Nemathorin Pheromone Traps last year found the results useful when making decisions on cropping and nematicide use and all plan to use the traps again this season, the firm said.

Results allow growers to identify high-risk fields and can form part of an Integrated Pest Management strategy, said the firm’s Alison Pawson. Beetle counts varied from 10 to over 240 on different fields across the same farm and up to 375 in one case, she said.

“In some instances, where very high click beetle counts indicated a large number of wireworm larvae in the soil (6% of fields trapped), growers have opted not to crop potatoes.

“In lower risk fields, many growers are going to apply Nemathorin [fosthiazate] at planting and/or plant crops that can be lifted earlier to minimise damage. Early warning of potential problems allows time for decision making to reduce damaging effects.”

But, while pheromone traps are claimed to be more effective than bait trapping or soil sampling at identifying wireworm risk, these other methods should still be used as a back-up, added ADAS’s Bill Parker.

Traps should be placed this year for fields destined for potatoes in 2007, he explained. They should be put out in sets of three at the end of April, in time for peak wireworm hatch and beetle activity in mid to late May.

Traps should be monitored and recorded weekly, with the pheromone capsule replaced every 30 days, he said.

The following table can be used to estimate crop damage from trap results:

Total trap catch per set of three traps Predicted wireworm population/ ha Approximate potato damage risk  

 Nil

None or very low 

None or very low 

 <50

 25,000-250,000

Some damage likely

 50-100

 150,000-250,000

Significant damage likely 

 >150

 >250,000

Severe damage likely