Watch for leafminers on mums in greenhouses

Some growers have found chrysanthemum leafminer on their spring mum crop. Insecticide resistance is a concern, so consider alternative products.

Over the last five years, more growers have reported problems with leafminers on greenhouse-grown chrysanthemums. Most likely the problem is due to leafminer resistance to insecticides. Growers have relied heavily on Avid (abamectin), Citation (cyromazine) and Conserve (spinodad) for leafminer control for at least 10 years.

In a study on leafminer resistance published in 2004, Scott Ferguson found that chrysanthemum leafminers collected from greenhouse growers producing mums or gerbera were highly resistant to two of three or all three insecticides (Avid, Conserve and Citation). The level of resistance depended on the location, but the average level of resistance was enough to cause poor control or complete failure of two of the three insecticides. For mums grown in 2014, it will be risky to rely on Avid, Conserve or Citation.

Michigan State University Extension advises growers to check cuttings when they arrive for leaf mines and begin scouting for leafminers once per week as soon as your crop is started. Yellow sticky cards are also helpful for spotting leafminer adults. When mines are found, remove the infested leaves and spray once per week with a foliar spray or drench once every six weeks with a systemic product. Some labels have restrictions on how many applications can be made per year.

Suggested products

Research is needed on what works best for resistant leafminers. Some alternatives to Avid, Citation and Conserve are listed below.

Soil drenches

  • Aria (flonicamid)
  • Flagship (tiomethoxam)
  • Imidacloprid (several products)
  • Safari (dinotefuran)
  • Tristar (acetamiprid)

However, leafminers could be resistant to these products, also.

Foliar sprays

  • Kontos (spiromefisen)
  • Pedestal (novaluron)
  • Orthene (acephate)

Please note that this spring there has been some concern about how the use of neonicotinoid soil drenches (Flagship, imidacloprid, Safari and Tristar) could affect bees after greenhouse-grown plants are sold. More research is needed on this subject. However, we do know that if foliar sprays are used instead of soil drenches, and if there is no insecticide residue on open flowers at the time of shipping, the plants should be safe for bees.

Dr. Smitley’s work is funded in part by MSU’s AgBioResearch.

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