Allium leafminer feeding damage on early green onions. Picture taken 16 April 2017 by S.McDermott.
At the end of March, we started setting up sticky traps for monitoring the adult flight of the Allium Leafminer (ALM) in our region. This past week, April 11th to April 17th, we had more local damage reported.
We have not captured allium leafminer adults on our sticky traps suggesting the populations are still low. A few adult ALM have been captured by sweep netting in the field and we expect populations to increase over the coming two weeks so control measures should be taken.
There is a "look-alike" fly, Phytomyza plantaginis, that can be mistaken for ALM. The main difference between the two species is size - P. plantaginis is about half the size of ALM. Our traps have captured several of P. plantaginis this past week.
Figure 2. The top image is Phytomyza plantaginis - allium leafminer "look-a-like" License by CBG Photography Group, Centre for Biodiversity Genomics. The bottom image is Phytomyza gymnostoma, the allium leafminer by Dana Roberts.
Currently, ALM has overwintered as a small brown pupa in plant tissue or in the soil where alliums were present in the fall. A sign of adult ALM activity is the distinct ovipositioning/ feeding damage as shown in the image. Dana Roberts had two adult ALM hatch April 8th - 9th 2017 from field-collected pupa. The newer reports of damage indicate that the adult flight is beginning.
For those in affected counties this pest is either active or will be soon. Last season Tim Elkner had numerous growers who were unaware of this pest. Those growers lost all or most of several spring allium crops so ALM can be a significant problem.
For more information about the allium leafminer the Pennsylvania Department of Agriculture and Penn State posted reports and a pest alert to these websites: