Beware leafminers in greenhouses

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.