Insect update for the week of July 4, 2011

Aphids, thrips and adult leaf tiers have been reported.

While visiting the local greenhouses in Kalamazoo and the surrounding areas, the common message has been insects that seem to plague the mums annually are present now.

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 we are using in the greenhouses are either systemic, translaminar or contact. Systemic is when the active ingredient is primarily taken up by the plant roots and moves within the vascular tissues. Depending on the characteristics of the chemical, the movement can either go up the plant through the xylem or down through the phloem.

Marathon is a systemic insecticide that moves up in the plant’s xylem (water conducting tissue). Many of the systemic products are water soluble material, making the active ingredient available to be taken up by the root system or leaves of the host plant. Translaminar insecticides like Overature and Pylon penetrate leaf tissue and move within the leaf, but do not move beyond the leaf. Dr. Cloyd describes it as a reservoir of active ingredient within the leaf. Translaminars are effective on the target insect that may be hiding on the underside of the leaf.

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.

Read MSU entomologist Dave Smitley’s article, Greenhouse Insect Management for 2011 to view the 2011 Insect Control Research Results.

If there are adult greenhouse leaf tiers 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, causing plants to be not marketable.

The slender, pale-green caterpillar is tapered towards both ends. The mature larvae have a darker green band along the back and with a broader, whitish-band along each side. Full grown larvae are 17 to 19 mm long. The adult moth has prominent, black compound eyes. The body and wings are clay brown. The wings are bordered by small, black dots and have irregular black lines running across them. The hind wings are boarder than the forewings. The legs are whitish and the antennae are 3/4 the length of the forewings. The wingspan is 18 to 19 mm.

Adult moth Larva feeding on mum
Left, Adult moth. Right, Larva feeding on a mum.

To manage the greenhouse leaf tier, most pyrethroids are effective. If the caterpillars are small and ingest the plant material treated, bacillus thuringiensis is an option.

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