Leafminer on mums

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.    

There are areas in Michigan where leafminers (Liliomyza trifolii) are being seen on the fall mum crop.

Life cycle

They have a fairly short life cycle that can be completed in 21 to 28 days under hot and humid conditions such as what we have experienced over the last two weeks. This allows for multiple generations to occur during the summer.

Adult stage

Small, less than 2 mm in length. The head and legs are yellow with red eyes. Look for them on your sticky cards. The female’s life expectancy is longer than the male’s since they pierce the leaf tissue with their ovipositor to feed and lay eggs where the males do not have that ability. The females can make numerous punctures and can lay up to 39 eggs per day.

Egg laying behavior

The females prefer older leaf surfaces for ovipositing (lower leaves of your mum plants for scouting purposes) and they tend to deposit them in the middle of the plant.


The egg hatches just below the epidermis and the larvae begin feeding and moving around making the serpentine damage due to the mining of the tissue. There are four instars and at each instar the insects body size increases. At the last instar, they can measure at approximate 0.25 mm. One positive factor is that over at 83°F, larvae experience mortality.


Dr. Dave Smitley recommends Avid and Citation. If you have stock plants, they should be treated before taking cuttings or spray new crop when it arrives and again two and four weeks later. We are beyond that at this time, so you need to begin your sprays as soon as possible if you have activity to reduce females activity.

There are a number of natural enemies; however, any insecticide spray applications for other pests on mums will eliminate or reduce their activity.

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