Jeanne Himmelein of Mich. St. Univ. Extension reports that insects that normally infest garden mums are now present. She said both aphids and thrips are easier to manage when the plant canopy is not fully developed, allowing for better spray coverage. Most of the insecticides being applied in greenhouses are either systemic, translaminar or contact.
Scouting for thrips is done by using both visual inspection and yellow or blue sticky cards. Thrips populations have been reported to be high on mums without flowers. When thrips enter the mum flowers, control can be difficult due to the inability to get the insecticide to penetrate the flowers where the thrips like to hide.
Himmelein said if adult greenhouse leaf tiers are flying around the area, then the larvae must be present. Make sure to scout deep in the canopy of the mums. Last year, damage from the larvae went unnoticed, resulting in unmarketable plants.